axon terminals or synaptic knob definition

l . Electrical events propagate a signal within a neuron, and chemical processes transmit the signal from one neuron to another or to a muscle cell. The chemical process of interaction between neurons and between neurons and effector cells occur at the end of the axon, in a structure called synapse

"Communication Between Nerve Cells By Silvia Helena Cardoso, Ph DIntroduction All of our sensations, feelings, thoughts, motor and emotional responses, learning and memory, the actions of psychoactive drugs, the causes of mental disorders, and any other function or dysfunction of the human brain cannot be understood without the knowledge about the fascinating process of communication between nerve cells (neurons).

Neurons must continuously gather information about the internal state of the organism and its external environment, evaluate this information, and coordinate activities appropriate to the situation and to the person's current needs.

How neurons process this information? This essentially happens by means of the nerve impulse. A nerve impulse is the transmission of a coded signal from a given stimulus along the membrane of the neuron, starting in the point where it was applied.

Nerve impulses can pass from one cell to another, thus creating a chain of information within a network of neurons. Two types of phenomena are involved in processing the nerve impulse: electrical and chemica

. Touching very close against the dendrite of another cell (but without material continuity between both cells), the axon releases chemical substances called neurotransmitters , which attach themselves to chemical receptors in the membrane of the following neuron and promote excitatory or inhibitory changes in its membrane.

Therefore, neurotransmitters make possible the nerve impulses of one cell influence the nerve impulses of another, thus allowing brain cells to ""talk to each other"", so to speak. The human body has developed a large number of these chemical messengers in order to facilitate internal communication and signal transmission within the brain. When everything is working properly, the internal communications take place without we even being aware of them.

An understanding of synaptic transmission is the key to understanding the basic operation of the nervous system at a cellular level. The whole point of the nervous system is to control and coordinate body function and enable the body to respond to, and act on, the environment. Synaptic transmission is the key process in the integrative action of the nervous system. We have already seen the electrical process of the nerve impulse in previous article.

In this issue, we are going to examine more closely how the synapse and neurotransmitters work.. Synapse: Meeting Point Between Neurons Since neurons form a network of electrical activities, they somehow have to be interconnected.

When a nerve signal, or impulse, reaches the ends of its axon, it has traveled as an action potential, or a pulse of electricity. However, there is no cellular continuity between one neuron and the next; there is a gap called synapse.

April 7, 2013refers to the end of an axon or an axon branch, which forms a synapse on a neuron or other target. See also terminal button. AXON TERMINAL: ""The axon terminal of a neuron is most commonly located at the end of the axon, nearest to the synaptic cleft .

AXON TERMINAL

"AXON TERMINALBy Nugent, Pam M. S. -

""Related Psychology Terms TERMINAL BUTTONAXO-AXONAL SYNAPSESYNAPSEAXON HILLOCKSYNAPTIC VESICLESYNAPTIC CLEFTRELEASE ZONEDALE'S LAWNERVE FIBERPOSTSYNAPTICCite this page: Nugent, Pam M. S., ""AXON TERMINAL,"" in Psychology Dictionary.org, April 7, 2013, https://psychologydictionary.org/axon-terminal/ (accessed March 31, 2018).tweet "

on Structural unit of the nervous system consisting of the nerve cell body and its variousprocesses, the dendrites, the axon and the ending (also called bouton, end foot or axonterminal).

bouton

"bouton (redirected from bouton terminal) Also found in: Dictionary, Encyclopedia. Related to bouton terminal: synaptic boutonsbouton [ boo-taw´] ( Fr.) button.bouton terminal [ ter-mĭ-nahl´] (pl. pl. boutons´ terminaux´) end-foot. Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition.

© 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.bou·ton ( bū-tōn [h]' ), A button, pustule, or knoblike swelling. [Fr. button]Farlex Partner Medical Dictionary © Farlex 2012bouton/bou·ton/ ( boo-tahn´) [Fr.] a buttonlike swelling on an axon where it has a synapsewith another neuron.synaptic bouton b. terminal.bouton terminal ( ter-mĭ-nahl´) pl.

boutons´ terminaux´ a buttonlike terminal enlargement of an axon that ends in relation to another neuron at a synapse. Dorland's Medical Dictionary for Health Consumers. © 2007 by Saunders, an imprint of Elsevier, Inc. All rights reserved.bouton [bo̅o̅tôN′, bo̅o̅′ton]Etymology: Fr, button1 a button, pustule, or knoblike swelling, such as the expanded end of an axon at a synapse (terminaux) which comes into contact with cell bodies of other neurons.2 a lesion associated with cutaneous leishmaniasis.3 a small abscess of the intestinal mucosa in amebic dysentery.

Mosby's Medical Dictionary, 9th edition. © 2009, Elsevier.bou·ton ( bū-tōn [h]') A button, pustule, or knoblike swelling. [Fr. button]Medical Dictionary for the Health Professions and Nursing © Farlex 2012bouton A swelling or thickening, especially on the skin. Collins Dictionary of Medicine © Robert M. Youngson 2004, 2005boutonsee SYNAPTIC KNOB. Collins Dictionary of Biology, 3rd ed.

© W. G. Hale, V. A. Saunders, J. P. Margham 2005axon The threadlike process of a neuron which conducts nerve impulses from the cell body to theneuron's ending (bouton) where it is transmitted via a synapse to another neuron, muscle or gland. Syn. nerve fibre (when it is sheathed). See neuron; synapse.neur

There are many types of neurons within the nervous system; some transmitafferent nerve impulses to the brain (e.g. those carrying information from the photoreceptors to the visual cortex), or to the spinal cord (e.g.

those carrying information from the receptors in the skin to the spinal cord). They are called sensory neurons. Others transmit efferentmotor nerve impulses to a muscle (e.g. those carrying information from the Edinger-Westphalnucleus to the sphincter pupillae and ciliary muscles). These are called motor neurons. Other neurons carry nerve impulses from one neuron to another ( internuncial neurons ).

Note: also spelt neurone. See action potential; synapse. Millodot: Dictionary of Optometry and Visual Science, 7th edition. © 2009 Butterworth-Heinemannbou·ton ( bū-tōn [h]') A button, pustule, or knoblike swelling. [Fr. button]Medical Dictionary for the Dental Professions © Farlex 2012bouton [Fr.]

button.bouton terminalthe swollen end of an axon that contributes to a synapse. Saunders Comprehensive Veterinary Dictionary, 3 ed. © 2007 Elsevier, Inc. All rights reserved Want to thank TFD for its existence? Tell a friend about us, add a link to this page, or visit the webmaster's page for free fun content . Link to this page:boutonFacebook Twitter "

nal Button-like endings of axons through which axons make synaptic contacts with other nerve cells or with effector cells Supplement Axon terminals refer to the axon endings that are somewhat enlarged and often club- or button-shaped. Axon terminals are that part of a nerve cell that make synaptic connections with another nerve cell or with an effector cell (e.g. muscle cell or gland cell ). Axon terminals contain various neurotransmitters and release them at the synapse.

Axon terminals

Axon terminalsnavigation search Definitionnoun, singular: axon termi

These neurotransmitters transmit electrical impulses to the target cell (neuron or effector) and the neuron that releases these neurotransmitters via the axon terminals is called a presynaptic neuron whereas the neuron that receives the impulse is called a postsynaptic neuron. The transmission of nerve impulse begins with an action potential traveling along the membrane of the presynaptic neuron until the synapse.

Electrical depolarization of the membrane at the synapse will lead to increased permeability to calcium ions. Influx of calcium ions activates calcium-sensitive proteins into releasing the neurotransmitters into the synaptic cleft. These neurotransmitters bind to the receptor molecules on the membrane of the postsynaptic neuron, activating the latter.

The neurotransmitters eventually break loose and may either be reabsorbed by the presynaptic neuron or broken down metabolically. Also called:axon terminal boutons Synonym (s):bouton terminauxend-feetneuropodia ( neuroanatomy)pieds terminauxsynaptic boutonssynaptic endingssynaptic terminalsterminal boutons See also:axon]]impulsenerve cellneuronneurotransmitterneurotransmitter vesiclepostsynaptic membranepresynaptic membranesynapsesynaptic vesicletelodendrion

It consists of the axon terminals of the pre synaptic neuron on one side, a small gap, called the synaptic cleft and the dendrites of the post synaptic neuron on the other side. Or it consists of a sensory receptor on one side, the synaptic cleft and the dendrites of a sensory neuron on the other side. Or it consists of the axon terminals of a motor neuron on one side, the synaptic cleft and the muscle, gland or organ on the other side.

Understanding Nerves and Neurons

Understanding Nerves and Neurons Nerves and neurons are the 'wiring' that allow the nervous system to control everything we do. Read this page and get yourself 'wired in'. The anatomy of nerves The nervous system is one of two key control systems of the body that sends and receives messages, enabling us to function properly. It is able to do this because of the nerves that connect the brain and spinal cord with our peripheral regions (legs and arms) and viscera (organs).

This connection allows the action potentials (impulses) to travel throughout the body, much like the wiring in your house.

What are nerves? Nerves are made up of cable-like bundles of nerve cells (neurons) and each neuron has three main parts, these are:1. dendrites2. cell body3. axon The dendrites receive impulses from sensory receptors or other neurons and send them towards the cell body, which contains the nucleus.

Impulses are then conducted along the axons full length away from the cell body to connect with the dendrites of another neuron, muscle, organ or gland of some kind. Some axons have a fatty covering called a myelin sheath as seen in the adjacent image. A myelin sheath is formed by Schwann cells that wrap around the axons. Schwann cells are spaced evenly apart, the gaps in-between them are called the ‘nodes of ranvier’.

Impulses can travel faster along neurons that have a myelin sheath as an impulse can jump from node to node. What do nerves do? All nerves have two main functions, these are: Receive signals: Nerves receive signals because they are irritable, meaning that they can respond to a stimulus.

Once a stimulus is received by a nerve cell it converts it to a neural impulse which passes along the nerve.

For example, if I touch something hot the nerve endings in my finger get ‘irritated’ and send a message (impulse) back to my brain to say ‘Ouch!’Transmit nerve impulses: Nerves are able to transmit impulses along the length of the nerve cell in the form of an electrical signal (like power lines). These electrical signals move from one end of the nerve cell to another and can pass from nerve to nerve (power pole to power pole). What are the properties of neurons? Neurons have two special properties that enable nerves to carryout their two main functions, these are:1.

Excitability / irritability: This means they can be stimulated to produce an impulse (action potential) – a tiny electrical current.2. Conductivity: This means neurons are also able to transfer an impulse along the full length of their axons and then on to other neurons, muscles or glands.

Like the electrical wiring in your house. Neurons are always excited by a stimulus first, before that stimulus is conducted to the next nerve, muscle or gland. A stimulus comes about by energy being delivered to the membrane of a neuron. There are several ways in which a stimulus can be received in order to excite a neuron.

How can a neuron be stimulated?1. A sound wave exciting neurons in the inner ear (E.g. A personal trainer providing instruction to a client on how to perform an exercise).2.

Heat exciting neurons in the skin (E.g. Information sent to the brain telling the sympathetic nervous system to increase sweating to cool the body).3. Light exciting neurons in the eye (E.g. A personal trainer providing a visual demonstration of an exercise for the client to repeat).4. Pressure or length change exciting the neurons in the muscles (E.g. Lifting a barbell to do a bench press and feeling the load as increased pressure).

What types of nerves are there? There are three different types of nerves, these are explained below and can be seen in the following image:1. Sensory neurons send impulses from sensory receptors to inform the CNS of a stimulus. A sensory receptor is a structure that recognises a change in its environment.

Sensory neurons have long dendrites and short axons. The dendrites of a sensory neuron are found outside the spinal cord in the skin, muscle or gland of their particular sensory receptor. Their axons end in the spinal cord where they connect with the dendrites of other neurons.2. Motor neurons send impulses from the CNS to the muscle, organ or gland they command to take action.

Motor neurons have short dendrites and long axons. Their dendrites and cell body are in the spinal cord and their axons are found in the muscle, organ or gland that they innervate. They can be over one metre long.3. Inter neurons receive information from other neurons and pass this information on to other neurons.

Their dendrites and axons are of similar length and are both found completely within the spinal cord or brain (CNS). In summary neurons are either:1. Sensory – receive information from the PNS2. Inter – pass information on in the CNS3. Motor – send information from the CNSHow are nerves organised and ‘joined’? Neurons meet with other neurons, sensory receptors and tissues at synapses. Synapses are junctions that allow neurons to communicate with each other, sense receptors, muscles and glands.

It is these synapses that make it possible for the CNS to form inter connected circuits. Communication across a synapse occurs in one direction only. Chemicals called neurotransmitters are released from the axon terminals of the pre synaptic neuron into the synapse (also called a synaptic cleft) and are received by the dendrites of the post synaptic neuron. The synapse is the control switch of the nervous system. It is here where information or commands sent as impulses can be passed on, changed or stopped. A synapse is created in several different ways depending on where in the body it’s located.

It consists of the axon terminals of the pre synaptic neuron on one side, a small gap, called the synaptic cleft and the dendrites of the post synaptic neuron on the other side. Or it consists of a sensory receptor on one side, the synaptic cleft and the dendrites of a sensory neuron on the other side. Or it consists of the axon terminals of a motor neuron on one side, the synaptic cleft and the muscle, gland or organ on the other side.

How do nerves conduct messages? Impulses that are sent along neurons are called action potentials. An action potential (also known as an impulse) is the electrical current that travels the length of an axon when a neuron has been stimulated. At rest the membrane inside of a neuron has a negative charge. This is called the resting membrane potential. The outside of the neurons membrane is positively charged at rest, as can be seen in the below diagram.

To send an action potential across the length of a neuron the charge across the membrane is reversed briefly (this is also known as depolarisation) and the charge within the membrane briefly becomes positive. As the charge passes, the membrane then re-polarises and returns to its resting (negatively charged) potential.

In the axon of an unmyelinated neuron an action potential travels along as a wave, as illustrated below.

A brief reversal of charge travelling the length of an unmyelinated axon In a myelinated neuron the potential jumps around the Schwann cell from node to node, as can be seen in the below diagram. The nodes of ranvier in myelinated neurons allow the action potential to jump along the axon at a higher speed than action potentials in unmyelinated neurons. How can nerves produce a ‘graded’ response? We don’t always want nerves to fire the next nerve because sometimes we want a graded response that primes the system for action.

For example if we were doing some warm up sets of squats prior to some very heavy sets, the warm up sets would prime most of the nerves in the relevant muscles, but the load (weight) wouldn’t be significant enough to require them all to fire. By not having all the nerves’ firing during the warm up precious energy is conserved for the heavy sets. By having the relevant nerves ‘primed’ for the heavy sets the messages will be ready to go directly to the target muscles ‘on mass’ when the load gets heavy, making for a more effective and efficient lift.

A graded potential is local depolarisation (i.e. at the dendrites involved) that may not meet the threshold required to depolarise the membrane of the neuron.

Each neuron has a threshold that must be met before an action potential travels the length of the neurons axon. All graded potentials travel from the dendrites toward the cell body and on to the axon hillock. The axon hillock is at the end of the cell body and it controls the firing of the neuron.

If the graded potential is enough to meet the threshold, it will depolarise the membrane and an action potential will travel the length of the axon. If it is not enough there will be no depolarisation across the membrane and an action potential will not occur.

Action potentials are self-propagated and once started they progress along the axon membrane. It is all-or-none; there are not different degrees of action potentials.

You either have one or you don't. How can nerves and their arrangement reduce or increase a response to a stimulus? Once an action potential has fired it will synapse with another neuron, muscle or gland. It will not always depolarise the neuron membrane, instead it could hyperpolarise it. When a neuron is hyperpolarised it is inhibited. Hyperpolarising makes the neuron membrane more negative. This means the threshold to depolarise the neuron is harder to reach making it less likely for an action potential to fire.

An action potential travels the length of the axon reaching the axon terminals. At this point the axon meets with another neuron, muscle or organ at a synapse. The action potential is transmitted through the synapse by the neurotransmitters. The neurotransmitters are received by receptors on the other side of the synapse. This transmission across the synapse can be inhibitory or excitory depending on the type of synapse.

The combination of the neurotransmitter and the receptor of the post-synaptic neuron determine the mode of transmission of the action potential.

If the transmission is inhibitory, the message that is received on the post-synaptic neuron is an Inhibitory post synaptic potential (IPSP), which results in the neuron membrane becoming hyperpolarised and therefore less likely to fire. If the transmission is excitory, the message that is received on the post-synaptic neuron is an Excitory post synaptic potential (EPSP) .

This will lead toward a depolarisation of the neuron membrane and an increase in the likely hood of firing. The adjacent image shows an inhibitory neuron (C), two excitory neurons (A and B) and the resultant depolarisation of neuron D. The post-synaptic neuron can synapse with more than one pre-synaptic neuron, as seen in the above image.

The arrangement of neurons synapsing together is set out according to the functions of the structures (muscles, glands, organs etc) the neurons service. An action potential will also only be generated in the post-synaptic neuron if the threshold is met.

This is achieved if the sum of all potentials, excitory and inhibitory, is received at the axon hillock and is above the threshold, as shown in the below image. If excitory and inhibitory potentials are received at the same time or in very quick succession then the inputs are added together ( summated) .

If there are enough excitory potentials to meet the threshold an action potential will be generated, as seen in the below image. Conversely if there are more inhibitory potentials then the threshold will not be met and the post-synaptic neuron will not propagate an action potential and the message will be blocked.

The summation of potentials can actually occur is two ways depending on how many pre-synaptic neurons are sending action potentials to the post-synaptic neuron. The two ways in which potentials can be summated are through temporal and spatial summation, as described and shown in the following table.

Temporal summation refers to two or more action potentials arriving frequently from one single pre-synaptic neuron, as seen in the below image. Spatial summation refers to two or more action potentials arriving at the same time from different pre-synaptic neurons, as seen in the below image. Why are IPSPs important? The location of inhibitory inter neurons in the spinal cord make it possible for action potentials to be inhibited.

Because we don’t want to be continuously acting on the multitude of messages from sensory neurons, inhibitory inter neurons are strategically placed within the network of connections between neurons. In this way the CNS can create an IPSP (inhibitory post-synaptic potential) which increases the amount of stimulus required for the action potential to continue through the post-synaptic neuron.

An example of this is our ability to stop from pulling our arm away when given an injection. Inhibitory post synaptic potentials are also important for allowing the body to perform movement.

When one muscle group contracts it is often necessary for its antagonist muscle group to relax. The antagonists are inhibited from contracting in what is called reciprocal inhibition. An example of this is your triceps relaxing when you do a bicep curl, if they didn’t you would not be able to bend your elbow.

Can the brain ‘prime’ or ‘tune in’ to a stimulus to help reflexes and movements? The brain can cause EPSP’s (excitory post-synaptic potentials) to make reflexes or movements more likely to occur. When we visualise or anticipate movements we can ‘prime’ the reflex or movement. An example is when you are going to catch a ball, you are usually prompted to have your hands up and ready, with fingers spread.

Often children will be told to ‘get ready, watch the ball’. In this way coaches are constantly asking kids to ‘prime’ or ‘tune in’ to stimuli that are important for performance of a task.

The same principles apply to training clients. For example if you are teaching a client to do back squats you may say things such as, “remember to squeeze your glutes and keep your chest up”. These are essentially cues that will get your client thinking about those technique points and will result in EPSP’s being sent to ‘prime’ the movement. Learned reflexes Many reflexes can be learnt by the CNS. The brain facilitates reflex pathways when we learn and practice new skills.

It is important to learn and practice correctly as once a technique becomes learned it is facilitated as an established reflex. To unlearn something is very difficult. This is a particularly important point when you think about all the new exercises that we will pattern in to our clients nervous systems in the first few sessions we have with them.

Perfect technique early will pay massive dividends long term and it’s just as easy to create as poor technique. Posture is also an example of a learned reflex. If a certain posture is assumed often it is difficult to change, we can shift to a better posture but slip back into a hunched position when not consciously thinking of it.

Examples of different postures can be seen in the following image. Learning to ride a bike or throw a ball are also learned reflex pathways. They are learned by repeating them over and over when you are young. Before an action is facilitated as a learned reflex pathway it is clumsy or uncoordinated. When the action is performed repetitively we become more efficient at it as our CNS sends out the correct EPSPs and IPSPs automatically. Eventually having a complete map of the movement recorded which we can execute quickly and efficiently whenever required.

When an electrical signal reaches the end of a neuron, Voltage-gated calcium channels open and allow Ca2+ to rush into the neuron's axon terminal (the very end of the neuron), which in turn makes the neuron release neurotransmitters that diffuse across the synaptic gap (the space between neurons).

What are neurotransmitters?

Science & Mathematics Biology What are neurotransmitters? Follow 8 answers Answers Relevance Rating Newest Oldest Best Answer: Its a chemical compound that helps transmit electrical signals from neuron to neuron.

Once they reach the other end, neuroreceptors in the 2nd neuron detect these neurotransmitters and help recreate the electrical signal that travels through the 2nd neuron.

This happens over and over. You can imagine that an agent that can somehow disrupt this mechanism can be used as anethesia, paralytic etc., depending on the kind of effect it has on neurotransmitters or neuroreceptors or both.amg · 8 years ago2 0 Comment Neurotransmitters Definition Source (s):https://shrink.im/a75Bdwheelwright · 2 years ago0 0 Comment What Are Neurotransmitters Source (s):https://shrinks.im/a7Wmzdilox · 1 year ago0 0 Comment Neurotransmitters are chemicals in the synapses between neurons that transfer the impulse for one neuron to another makings a chain from where the stimulus occurs to the brain.

Stepha P · 8 years ago0 0 Comment Neurotransmitters are chemicals that transmit information between nerve endings. They are messed up by drugs such as cocaine which makes the drug dangerous because the effect is indescriminate.

Gibson Ess Gee · 8 years ago0 0 Commentits a chip they put in your head when your a baby and watch you through out your life from space that's why you get headaches.have you yahoo'd it to see what pops upbo · 8 years ago0 0 Comment It's how your brain and body communicate without you being aware of it.sandy eggo · 8 years ago0 0 Comment An ipod that is too close to your head.

Veronica · 8 years ago0 0 Comment Maybe you would like to learn more about one of these? Earn your MBA online! How to order contacts online? Explore Digital Home Security Try online nursing courses?

oad Anatomy Neurons are the cells that compose your nervous system. These consist of a body that receives a nerve transmission as well as an axon that signals the transmission. The axon terminates in branches called synaptic knobs which innervate the cell that the impulse is traveling to.

Calcium and Nerve Impulses

Calcium and Nerve Impulsesby LAURA NIEDZIOCHA Oct. 03, 2017Calcium, a positively charged molecule, is useful many places within the human body. The role of calcium inside the nervous system extends from the initiation of a nerve signal to the action taking place.

Calcium signals an impulse to a muscle cell and continues to be useful until the contraction is complete. Video of the Day Error loading player: Flash plugin failed to l

Nerve Impulse Conduction A nerve impulse begins conduction as electrical impulses, initiated by the brain, travel down through nervous system cells. The electricity causes a change in polarity by opening channels to move positive sodium or potassium ions in or out.

Positive molecules are stored in membranes guarded by gated channels. This means they must be stimulated in order to release the positive ions which help to conduct the nerve impulse. Nerve Impulse and Calcium It is well-known that calcium is another positive molecule useful for the conduction of a nerve impulse to a muscle fiber.

However, Clay Armstrong, a neurobiologist, believes that calcium may play a larger role. Armstrong suspects that calcium is in charge of the gated channels that release potassium and sodium to facilitate a nerve impulse. Armstrong's theory proposes that calcium ions are like a door to these gated channels. Calcium must move to release the ions and calcium must return before the impulse will stop and homeostasis is returned.

Calcium and Muscle Contractions When a nerve impulse reaches a muscle cell, movement of the muscle requires calcium as well. Your muscle cells store calcium and upon nerve impulse, the cell is flooded with calcium. In order for a skeletal muscle to move, two myofilaments, actin and myosin, inside a muscle fiber must bind to one another to create a pulling action which shortens the muscle.

However, a molecule known as tropomyosin blocks the binding site and must be moved to create a contraction. Calcium binds to troponin which is attached to tropomyosin. Upon binding with calcium, troponin moves tropomyosin, exposing the binding site and creating movement.

Lose Weight. Feel Great!Change your life with My Plate by LIVE STRONG . COMGOALGENDER AGEWEIGHT HEIGHTGET MY CALORIE GOALYOU MIGHT ALSO LIKEThe Effect of Calcium on the Liver Does Calcium Help Muscles Contract? What Foods & Minerals Deplete Calcium? How to Lower Calcium Levels What Are the Causes of Too Much Calcium in Urine? Can I Take Calcium While on Cipro? High Calcium & Albumin Does Calcium Interfere With Clindamycin? A Calcium Supplement That Does Not Constipate Low Vitamin D & Muscle Twitching What Are the Causes of Severe Calcium Deficiency?

Are TUMS a Good Calcium Supplement? Can Calcium Be Absorbed Without Magnesium? The Effects of Too Much Calcium in the Brain Calcium Intake and Salivary Gland Stone Formation Vitamins Not to Mix With Calcium The Side Effects of Calcium Caltrate vs. Calcium Citrate Electrolytes in Lemons What Factors Influence an Electrolyte Imbalance? Can Too Much Calcium in Diet and Supplements Cause Breast Calcifications?

ter A chemical substance that is released into the synaptic cleft from the axon terminal of a sending neuron, crosses a synapse, and binds to apprpriate receptor sites on the dendrites or cell body of a receiving neuron, influencing the cell either to fire or not to fire. Receptors

Psychology Chapter 2

"81 terms misslissa328Psychology Chapter 2Learn Flashcards Write Spell Test Match Gravity Advertisement Upgrade to remove ads Like this study set?

Create a free account to save it. Create a free account Maybe later Sort Neuron A specialized cell that conducts impulses through the nervous system and contains three major parts--a cell body, dendrites, and an axon.

Cell Body The part of a neuron that contains the nucleus and carries out the metabolic functions of the neuron. Dendrites In a neuron, the branchlike extensions of the cell body that recieve signals from other neurons.

Axon The slender, tail-like extension of the neuron that transmits signals to the dendrites or cell body of other neurons and to muscles, glands, and other parts of the body. Glial Cells Specialized cells in the brain and spinal cord that hold neurons together, remove waste products such as dead neurons, and perform other manufacturing, nourishing, and cleanup tasks.

Synapse The junction where the axon terminal of a sending neuron communicates with a receiving neuron across the synaptic cleft. Resting Potential The slight negative electrical potential of the axon membrane of a neuron at rest, about -70 millivolts.

Action Potential The sudden reversal of the resting potential, which initiates the firing of a neuron. Myelin sheath The white, fatty coating wrapped around some axons that acts as insulation and enables impulses to travel much faster. Neurotransmit

Protein Molecules on the surfaces of dendrites and cell bodies that have distinctive shapes and will interact only with specific neurotransmitters. Reuptake The process by which neurotransmitters are taken from the synaptic cleft back into the axon terminal for later us, thus terminating their excitatory or inhibitory effect on the receiving neuron. Acetylcholine A neurotransmitter that plays a role in learning new information, causes the skeletal muscle fibers to contract, and keeps the heart from beating too rapidly. Dopamine A neurotransmitter that plays a role in learning, attention, movement, and reinforcement; neurons in the brains of those with Parkinson's disease and schizophrenia are less sensitive to its effects.

Norepinephrine A neurotransmitter affecting eating, alertness and sleep. Epinephrine A neurotransmitter that affects the metabolism of glucose and nutrient energy stored in muscles to be released during strenuous exercise. Serotonin A neurotransmitter that plays an important role in regulating mood, sleep, impulsivity, aggression, and appetite. Glutamate Primary excitatory neurotransmitter in the brain. Gaba Primary inhibitory neurotransmitter in the brain.

Endorphins Chemicals produced naturally by the brain that reduce pain and the stress of vigorous exercise and positively affect mood. Central Nervous System (CNS) The part of the nervous system comprising the brain and the spinal cord. Peripheral Nervous System (PNS) The nerves connecting the central nervous system to the rest of the body.

Spinal Cord An extension of the brain, from the base of the brain through the neck and spinal column, that transmits messages between the brain and the peripheral nervous system.

Hindbrain A link between the spinal cord and the brain that contains structures that regulate physiological functions, including heart rate, respiration, and blood pressure. Brainstem The structure that begins at the point where the spinal cord enlarges as it enters the brain and handles functions critical to physical survival.

It includes the medulla, the pons, and the reticular formation. Medulla The part of the brainstem that controls heartbeat, blood pressure, breathing, coughing, and swallowing. Reticular Formation A structure in the brainstem that plays a crucial role in arousal and attention and that screens sensory messages entering the brain. Cerebellum The brain structure that helps the body execute smooth, skilled movements and regulates muscle tone and posture.

Substantia Nigra The structure in the midbrain that controls unconscious motor movements. Midbrain Area that contains structures linking the physiological functions of the hindbrain to the cognitive functions of the forebrain. Forebrain The largest part of the brain, where cognitive functions as well as many of the motor functions of the brain are carried out.

Thalamus The structure, located above the brainstem, that acts as a relay station for information flowing into or out of the forebrain.

Hypothalamus A small but influential brain structure that regulates hunger, thirst, sexual behavior, internal body temperature, other body functions, and a wide variety of emotional behaviors. Limbic System A group of structures in the midbrain, including the amygdala and hippocampus, that are collectively involved in emotional expression, memory, and motivation.

Amygdala A structure in the limbic system that plays an important role in emotion, particularly in response to unpleasant or punishing stimuli. Hippocampus A structure in the limbic system that plays a central role in the storing of new memories, the response to new or unexpected stimuli, and navigational ability.

Sympathetic Nervous System The division of the autonomic nervous system that mobilizes the body's resources during stress and emergency, preparing the body for action. Parasympathetic Nervous System The division of the autonomic nervous system that brings the heightened bodily responses back to normal following an emergency.

Electroencephalogram (EEG) A record of brain wave activity made by a machine called the electroencephalograph. Beta Wave The brainwave pattern associated with mental or physical activity. Alpha Wave The brainwave pattern associated with deep relaxation. Delta Wave The brainwave pattern associated with slow-wave (deep) sleep. Microelectrode A small wire used to monitor the electrical activity of or stimulate activity within a single neuron.

CT Scan (computerized axial tomography) A brain-scanning technique that uses a rotating, computerized X-ray tube to produce cross-sectional images of the structures of the brain. MRI (magnetic resonance imagery) A diagnostic scanning technique that produces high-resolution images of the structures of the brain.

PET Scan (position-emission tomography) A brain-imaging technique that reveals activity in various parts of the brain, based on patterns of blood flow, oxygen use, and glucose consumption. Functional MRI (f MRI) A brain-imaging technique that reveals both brain structure and brain activity more precisely and rapidly than PET.

Cerebrum The largest structure of the human brain, consisting of the two cerbral hemispheres connected by the corpus callosum and covered by the cerebral cortex. Cerebral Hemispheres The right and left halves of the cerebrum, covered by the cerebral cortex and connected by the corpus callosum; they control movement and feeling on the opposing sides of the body.

Corpus Callosum The thick band of nerve fibers that connects the two cerbral hemispheres and makes possible the transfer of information and the synchronization of activity between the hemispheres. Cerebral Cortex The gray, convulted covering of the cerbral hemispheres that is responsible for the higher mental processes of language, memory, and thinking. Association Areas Areas of the cerebral cortex that house memories and are involved in thought, perception, and language. Lateralization The specialization of one of the cerebral hemispheres to handle a particular function.

Left Hemisphere The hemisphere that controls the right side of the body, coordinates complex movements, and, in most people, handles most of the language functions. Right Hemisphere The hemisphere that controls the left side of the body and, in most people, is specialized for visual-spatial perception.

Split-brain Operation A surgical procedure, performed to treat severe cases of epilepsy, in which the corpus callosum is cut, separating the cerebral hemispheres. Frontal Lobes The largest of the brain's lobes, which contain the motor cortex, Broca's area, and the frontal association areas. Motor Cortex The strip of tissue at the rear of the frontal lobes that controls voluntary body movement and participates in learning and cognitive events.

Broca's Area The area in the frontal lobe, usually in the left hemisphere, that controls the production of speech sounds. Broca's Aphasia An impairment in the physical ability to produce speech sounds or, in extreme cases, an inability to speak at all; caused by damage to Broca's area.

Parietal Lobes The lobes that contain the somatosensory cortex (where touch, pressure, temperature, and pain register) and other areas that are responsible for body awareness and spatial orientation. Somatosensory Cortex The strip of tissue at the front of the parietal lobes where touch, pressure, temperature, and pain register in the cerebral cortex.

Occipital Lobes The lobes that are involved in the reception and interpretation of visual information; they contain the primary visual cortex. Primary Visual Cortex The area at the rear of the occipital lobes where vision registers in the cerbral cortex.

Temporal Lobes The lobes that are involved in the reception and interpretation of auditory information; they contain the primary auditory cortex, Wernicke's area. Primary Auditory Cortex The part of each temporal lobe where hearing registers in the cerebral cortex. Wernicke's Area The language area in the left temporal lobe involved in comprehending the spoken word and in formulating coherent speech and written language.

Wernicke's Aphasia Aphasia that results from damage to Wernicke's area and in which the person's speech is fluent and clearly articulated but does noto make sense to listeners. Pruning The process through which the developing brain eliminates unnecessary or redundant synapses.

Plasticity The capacity of the brain to adapt to changes such as brain damage. Endocrine System A system of ductless glands in various parts of the body that manufacture hormones and secrete them into the bloodstream, thus affecting cells in other parts of the body.

Hormone A chemical substance that is manufactured and released in one part of the body and affects other parts of the body.

Pituitary Gland The endocrine gland located in the brain that releases hormones that activate other endocrine glands as well as growth hormone; ""master gland. ""Adrenal Glands A pair of endocrine glands that release hormones that prepare the body for emergencies and stressful situations and also release corticoids and small amounts of the sex hormones. Genes The segments of DNA that are located on the chromosomes and are the basic units for the transmission of all hereditary traits.

Chromosomes Rod-shaped structures in the nuclei of body cells, which contain all the genes and carry all the genetic information necessary to make a human being.

Genotype An individual's genetic makeup. Phenotype An individual's actual characteristics. Dominant-recessive Pattern A set of inheritance rules in which the presence of a single dominant gene causes a trait to be expressed but two genes must be present for the expression of a recessive trait. Multifactorial Inheritance A pattern of inheirtance in which a trait is influenced by both genes and environmental factors. Behavioral Genetics A field of research that uses twin studies and adoption studies to investigate the relative effects of heredity and environment on behavior. "

ses 1) Dendrites conduct impulses toward the cell body 2) Axons conduct impulses away from the cell body 3) Axons end in axonal terminants 4) Axonal terminals are separated from the next neuron by a gap

"""The nervous system"""

"62 terms chantale""The nervous system""1) Functions and structure, of the nervous system. Learn Flashcards Write Spell Test Match Gravity Advertisement Upgrade to remove ads Sort Sensory Intput 1) Gather Information 2) To monitor changes occuring inside and outside the body 3) Changes or stimuli Integration To process and interpret sensory input and decide if action is needed.

Motor Output 1) a response to integrated stimuli 2) The response activities muscles or glands Central nervous System (CNS) Brain and the spinal cord Peripheral nervous system (PNS) Nerves outside the brain and spinal cord.

(spinal nerves and cranial nerves)Motor (efferent) neurons Nerves that carry impulses to the central nervous system to the viscera or glands.

Motor (efferent) division Nerves that carry impulses away from the central nervous system Subdivision of the Peripheral nervous system 1) Somatic voluntary nervous system 2) autonomic involuntary nervous system Support cells are made from connective tissue Support cells functions Are to support, insulate, and protect neurons. Astrocytes 1) Control the chemical of the brain 2) Form blood brain barrier (BBB) between capilaries and neurons.

3) Abundant star shaped cells and brace neurons. Microglia Spiderlike phagocytes and disposed of debris. Ependymal cells line cavities od the brain, spinal cord and it also circulate cerebrospinal fluid.oligodendrocytes Produce myelin sheath and are wraped aroundnerve fibers in the central nervous system Satellite cells Protect neuron cell bodies Schwann cells forms myelin sheath in PNS in jelly roll-like fashion Myelin sheaths Whitish, fatty mateial covering axons.

They are also synthesize by CNSNephrons Nerves in the kidneys Component of the cell body Nissl Substance, Neurofibrils, Nucleus, large nucleolus Nissl substance Specialized rough endoplasmic ERNeurofibrils Intermediated cytoskeleton, Maintain cell shape. Nerves proces

Synaptic cleft gap between adjacent neurons Synapse Junction between nerves ( comunication point of two neurons)Node of Ranvier gaps in myelin sheath along the axon Gray Matter Cell bodies and un myelinated fibers.basal Nuclei Clusters of the cell bodies within the white matter of the central nervous.

Ganglia (PNS) Collections of cells bodies outside the central nervous system Sensory (Afferent) neurons 1) Carry impulses from the sensory receptors to the CNS 2) Cutaneous sense organs 3) Propriceptors (sense of postition) - detect stretch or tension Interneurons Found in neural pathways inthe central nervous system an it connect sensory motor neurons.

Multipolar neurons many extension from the cell body Bipolar neurons One axon and on dentriteunipolar neurons have a short single process leaving the cell body Functional propeerties of neurons irritability, and conductivity Irritability Ability to respond to a stimuliconductivity Ability to transmit an impulse Polorization Fewer positive ions are inside the cell than outside the cell Depolorization membrane allows sodium (Na+) to flow inside the member because of a stimulus Repolorization Potassium ion (K) goes out the neurons cell ATP energy pumped sodium ion (Na+) out of the cell Ation potential 1) If the actrion potential starts, it is propagated over the entire axon.

2) impulses travel faster when fibers have a myelin sheath Transmission of a signal at sypanases 1) Impulses are able to cross the sypnase to aothe nerve.

2) Neurotransmitter is released from a nerve's axon terminal 3) The dendrite of the next neuron has receptors that are stimulated by neurotransmitter 4) an action potential is started in the dendrite Reflex Rapid, predictable and involuntary response to a stimulus.reflex arc the connection of the afferent neurons to the interneurons to the efferent neurons, resulting in a reflex actionsomatic reflex reflex which controls skeletal muscle contractionsautonomic reflexes smooth muscle regulation, heart and blood pressure regulation, regulation of glands, digestive system regulationregions of the brain Cerebral hemispheres (cerebrum), Clencephalon, Brain Stem, Cerebellum Layers of the cerebrum (Cerebral hemispheres) Gray matter, white matter, corpus collosum, basal Nucleigeay matter the outer layer in the cerebral cortex composed of mostly neuron cell bodieswhite matter fiber tracts deep to the gray mattercorpus callosum connects hemisphersbasal nuclei island of gray matter within the white matter Diencephalin Sits on top of the brain stem, it enclosed by the cerebral hemisphere and made of three parts.

Thalmus, hypothalmus, epithalmus. Thalmus surround the third ventrical, relay station for sensory impulsesm transfer impulses to the correct cortex for localizin, and interpreting.hypothalmus locate under thalmus.

an autonomis nervous system. responsible for regulating body temp and metabolism, control water balance.epithalmus forms root of the third ventricle. house the pineal gland, include chorochoid plexus that forms cerebrospinal fluid.brain stem attaches to the spinal cord. different parts of brain stem are midbrain, pons, and medulla oblongata, reticular formation. Midbrain reflex center for hearingpons bulging part of the brain stem, composed of fiber tracts, and control breathing.medulla oblongata lowest part of the brain stem.

merges into spinal cord control center for vital signs except temperature.reticular formation diffuse mass of gray matter. involved in visceral organ control plays role in awake/sleep cycle and consciousnesscerebellum provide involuntay coordination of body movements. two hemispheres with convoluted surfaces.nervous system protection Scalp, skin, skull, vertebral column, dura mater, arachnoid layer, spinalcerebral fluid, and pia mater. "

In most cases, a neurotransmitter is released from the axon terminal after an action potential has reached the synapse. The neurotransmitter then crosses the synaptic gap to reach the receptor site of the other cell or neuron.

Psychology: Neuron Structure

"13 terms elizabeth43335Psychology: Neuron Structure Learn Flashcards Write Spell Test Match Gravity Advertisement Upgrade to remove ads Sort Neuron Nerve cell.

Basic unit of the nervous system that communicates information to each other by means of electrochemical processes. Same with other cells: --Surrounded by a membrane. --Has a nucleus that contains genes. --Contains cytoplasm, mitochondria, and other organelles. Different from other cells: --Specialized projections called dendrites & axons. --Within neuron, signal is electrical while communication between is based on chemical processes. --Neurons form specialized connections called synapses and produce special chemicals called ""neurotransmitters"" that are released at the synapse.

Dendrites Branch-like processes that protrude from the soma and that receive input from other neurons.

Axons Long process that extends from the soma and is responsible for transmitting the neuron's signal from the soma to the terminal buttons (it carries impulse away from cell body); the axon typically splits in many little branches that each have terminal buttons at the end. Soma The cell body. Containing (a) the nucleus that holds the DNA and (b) several organelles that are supporting the neuron's metabolism.

Terminal Buttons At the end of the axon's branches and form synapses with the dendrites of other neurons. Neurotransmitters (Types) 1. Excitatory: Firing increases (increases likelihood that neuron will fire an action potential.) Ex: epinephrine & norepinephrine. 2. Inhibitory: Firing decreases (decreases likelihood that neuron will fire an action potential.)

Ex: serotonin & GABA Has to fit into the receptor. Presynaptic & Postsynaptic: Neurotransmitter goes into synaptic space and binds to protein called receptor on post synaptic neuron. How Neurotransmitters Work (Yahoo)

Then, in a process known as reuptake, the neurotransmitter attaches to the receptor site and is reabsorbed by the neuron. Action Potential Electrical signal that travels along the axon and causes release of chemicals from the terminal buttons. When the action potential reaches the end of the axon, synaptic vesicles open and release neurotransmitters which are picked up by the receiving dendrites. Action potentials=all or none (either fires or not) Firing strength doesn't change, but rate does.

Synapse Space between axon and dendrite. INFORMATION FLOW IN NEURONS -If neuron is stimulated it produces ACTION POTENTIAL (electric impulse) that travels down the axon. -Terminal buttons contain neurotransmitters. When action potential reaches terminal button, neurotransmitters are released through the presynaptic membrane into the synaptic cleft.

-Neurotransmitters then bind onto specific receptor cites on the postsynaptic membrane (dendrites) of another neuron. -If connections are excitatory, the probability that this neuron will fire increases. If these connections are inhibitory, the probability that this neurons will fire decreases. ----Neuron receives inhibitory and excitatory inputs from many different neurons at the same time. ----Net stimulation=sum of all postsynaptic inputs ----Neuron will fire an action potential only if net stimulation exceeds threshold.

In Detail: Resting Potential Inside (-) Outside (+) & Gated Channels are closed, Sodium Potassium Pump needed to maintain resting potential. Ions move from areas of low concentration to high concentration (for equilibrium): the ions move against concentration gradient. In Detail: Action Potential Inside (+), Outside (-) & Gated Channels are opened-first Sodium to switch concentration gradient, then potassium to switch back to resting potential.

Action Potentials are caused by an exchange of ions across the neuron membrane. -If neuron is depolarized at axon hillock (threshold) action potential is generated. -This causes sodium channels to open. Because there are many more sodium ions on the outside, and the inside of the neuron is negative relative to the outside, sodium ions rush into the neuron.=brief reversal of membrane potential Grandmother cells Or gnostic neuron, is a hypothetical neuron that represents a person's grandmother, or, any complex and specific concept or object.

-Gets activated when a person ""sees, hears, or otherwise sensibly discriminates"" his or her grandmother. (Ex: one cell codes Jennifer Aniston) Opposite (more accepted): Distributed representation theory=specific stimulus is coded by its unique pattern of activity over a group of neurons. "

An axon, at its most basic, is a tube-like structure that carries an electrical impulse from the cell body (or from another cell’s dendrites) to the structures at opposite end of the neuron—axon terminals, which can then pass the impulse to another neuron.

Neurons

Introducing the Neuron Neurons are specialized cells that transmit chemical and electrical signals to facilitate communication between the brain and the body. Learning Objectives Detail the structures and functions of each type of neuron Key Takeaways Key Points Neurons are specialized cells that transmit chemical and electrical signals in the brain; they are the basic building blocks of the central nervous system.

The primary components of the neuron are the soma (cell body), the axon (a long slender projection that conducts electrical impulses away from the cell body), dendrites (tree-like structures that receive messages from other neurons), and synapses (specialized junctions between neurons).

Some axons are covered with myelin, a fatty material that acts as an insulator and conductor to speed up the process of communication. Sensory neurons are neurons responsible for converting external stimuli from the environment into corresponding internal stimuli.

Motor neurons are neurons located in the central nervous system (CNS); they project their axons outside of the CNS to directly or indirectly control muscles. Interneurons act as the “middle men” between sensory and motor neurons, which convert external stimuli to internal stimuli and control muscle movement, respectively. Key Termsglial cell: Non-neuronal cells that provide structure and support to neurons.synapse: The junction between the terminal of a neuron and either another neuron or a muscle or gland cell, over which nerve impulses pass.myelin: A white, fatty material composed of lipids and lipoproteins that surrounds the axons of nerves and facilitates swift communication.nodes of Ranvier: Periodic gaps in the myelin sheath where the signal is recharged as it moves along the axon.

The neuron is the basic building block of the brain and central nervous system. Neurons are specialized cells that transmit chemical and electrical signals. The brain is made up entirely of neurons and glial cells, which are non-neuronal cells that provide structure and support for the neurons. Nearly 86 billion neurons work together within the nervous system to communicate with the rest of the body.

They are responsible for everything from consciousness and thought to pain and hunger. There are three primary types of neuron: sensory neurons, motor neurons, and interneurons. Structures of a Neuron In addition to having all the normal components of a cell (nucleus, organelles, etc.) neurons also contain unique structures for receiving and sending the electrical signals that make neuronal communication possible.

The structure of a neuron: The above image shows the basic structural components of an average neuron, including the dendrite, cell body, nucleus, Node of Ranvier, myelin sheath, Schwann cell, and axon terminal. Dendrite Dendrites are branch-like structures extending away from the cell body, and their job is to receive messages from other neurons and allow those messages to travel to the cell body.

Although some neurons do not have any dendrites, other types of neurons have multiple dendrites. Dendrites can have small protrusions called dendritic spines, which further increase surface area for possible connections with other neurons. Cell Body Like other cells, each neuron has a cell body (or soma) that contains a nucleus, smooth and rough endoplasmic reticulum, Golgi apparatus, mitochondria, and other cellular components. Axon

The cell body contains a specialized structure, the axon hillock, which serves as a junction between the cell body and the axon. Synapse

The synapse is the chemical junction between the axon terminals of one neuron and the dendrites of the next. It is a gap where specialized chemical interactions can occur, rather than an actual structure.

Neurons

The cell body contains a specialized structure, the axon hillock, which serves as a junction between the cell body and the axon. Synapse The synapse is the chemical junction between the axon terminals of one neuron and the dendrites of the next. It is a gap where specialized chemical interactions can occur, rather than an actual structure. Function of a Neuron The specialized structure and organization of neurons allows them to transmit signals in the form of electric impulses from the brain to the body and back.

Individually, neurons can pass a signal all the way from their own dendrites to their own axon terminals; but at a higher level neurons are organized in long chains, allowing them to pass signals very quickly from one to the other.

One neuron’s axon will connect chemically to another neuron’s dendrite at the synapse between them. Electrically charged chemicals flow from the first neuron’s axon to the second neuron’s dendrite, and that signal will then flow from the second neuron’s dendrite, down its axon, across a synapse, into a third neuron’s dendrites, and so on.

This is the basic chain of neural signal transmission, which is how the brain sends signals to the muscles to make them move, and how sensory organs send signals to the brain.

It is important that these signals can happen quickly, and they do. Think of how fast you drop a hot potato—before you even realize it is hot. This is because the sense organ (in this case, the skin) sends the signal “This is hot!” to neurons with very long axons that travel up the spine to the brain.

If this didn’t happen quickly, people would burn themselves. Other Structures Dendrites, cell bodies, axons, and synapses are the basic parts of a neuron, but other important structures and materials surround neurons to make them more efficient. Myelin Sheath Some axons are covered with myelin, a fatty material that wraps around the axon to form the myelin sheath.

This external coating functions as insulation to minimize dissipation of the electrical signal as it travels down the axon. Myelin’s presence on the axon greatly increases the speed of conduction of the electrical signal, because the fat prevents any electricity from leaking out.

This insulation is important, as the axon from a human motor neuron can be as long as a meter—from the base of the spine to the toes. Periodic gaps in the myelin sheath are called nodes of Ranvier. At these nodes, the signal is “recharged” as it travels along the axon.

Glial Cells The myelin sheath is not actually part of the neuron. Myelin is produced by glial cells (or simply glia, or “glue” in Greek), which are non-neuronal cells that provide support for the nervous system.

Glia function to hold neurons in place (hence their Greek name), supply them with nutrients, provide insulation, and remove pathogens and dead neurons. In the central nervous system, the glial cells that form the myelin sheath are called oligodendrocytes; in the peripheral nervous system, they are called Schwann cells.

Neuron in the central nervous system: This neuron diagram also shows the oligodendrocyte, myelin sheath, and nodes of Ranvier. Types of Neurons There are three major types of neurons: sensory neurons, motor neurons, and interneurons. All three have different functions, but the brain needs all of them to communicate effectively with the rest of the body (and vice versa).

Sensory Neurons Sensory neurons are neurons responsible for converting external stimuli from the environment into corresponding internal stimuli. They are activated by sensory input, and send projections to other elements of the nervous system, ultimately conveying sensory information to the brain or spinal cord. Unlike the motor neurons of the central nervous system (CNS), whose inputs come from other neurons, sensory neurons are activated by physical modalities (such as visible light, sound, heat, physical contact, etc.)

or by chemical signals (such as smell and taste). Most sensory neurons are pseudounipolar, meaning they have an axon that branches into two extensions—one connected to dendrites that receive sensory information and another that transmits this information to the spinal cord. Multipolar and pseudounipolar neurons: This diagram shows the difference between: 1) a unipolar neuron; 2) a bipolar neuron; 3) a multipolar neuron; 4) a pseudounipolar neuron. Motor Neurons Motor neurons are neurons located in the central nervous system, and they project their axons outside of the CNS to directly or indirectly control muscles.

The interface between a motor neuron and muscle fiber is a specialized synapse called the neuromuscular junction. The structure of motor neurons is multipolar, meaning each cell contains a single axon and multiple dendrites.

This is the most common type of neuron. Interneurons Interneurons are neither sensory nor motor; rather, they act as the “middle men” that form connections between the other two types. Located in the CNS, they operate locally, meaning their axons connect only with nearby sensory or motor neurons. Interneurons can save time and therefore prevent injury by sending messages to the spinal cord and back instead of all the way to the brain. Like motor neurons, they are multipolar in structure.

Neurons

Introducing the Neuron Neurons are specialized cells that transmit chemical and electrical signals to facilitate communication between the brain and the body. Learning Objectives Detail the structures and functions of each type of neuron Key Takeaways Key Points Neurons are specialized cells that transmit chemical and electrical signals in the brain; they are the basic building blocks of the central nervous system.

The primary components of the neuron are the soma (cell body), the axon (a long slender projection that conducts electrical impulses away from the cell body), dendrites (tree-like structures that receive messages from other neurons), and synapses (specialized junctions between neurons).

Some axons are covered with myelin, a fatty material that acts as an insulator and conductor to speed up the process of communication. Sensory neurons are neurons responsible for converting external stimuli from the environment into corresponding internal stimuli.

The neuron is the basic building block of the brain and central nervous system. Neurons are specialized cells that transmit chemical and electrical signals. The brain is made up entirely of neurons and glial cells, which are non-neuronal cells that provide structure and support for the neurons. Nearly 86 billion neurons work together within the nervous system to communicate with the rest of the body.

They are responsible for everything from consciousness and thought to pain and hunger. There are three primary types of neuron: sensory neurons, motor neurons, and interneurons. Structures of a Neuron In addition to having all the normal components of a cell (nucleus, organelles, etc.) neurons also contain unique structures for receiving and sending the electrical signals that make neuronal communication possible.

The structure of a neuron: The above image shows the basic structural components of an average neuron, including the dendrite, cell body, nucleus, Node of Ranvier, myelin sheath, Schwann cell, and axon terminal. Dendrite Dendrites are branch-like structures extending away from the cell body, and their job is to receive messages from other neurons and allow those messages to travel to the cell body.

Although some neurons do not have any dendrites, other types of neurons have multiple dendrites. Dendrites can have small protrusions called dendritic spines, which further increase surface area for possible connections with other neurons. Cell Body Like other cells, each neuron has a cell body (or soma) that contains a nucleus, smooth and rough endoplasmic reticulum, Golgi apparatus, mitochondria, and other cellular components. Axon

An axon, at its most basic, is a tube-like structure that carries an electrical impulse from the cell body (or from another cell’s dendrites) to the structures at opposite end of the neuron—axon terminals, which can then pass the impulse to another neuron.

The cell body contains a specialized structure, the axon hillock, which serves as a junction between the cell body and the axon. Synapse

The synapse is the chemical junction between the axon terminals of one neuron and the dendrites of the next. It is a gap where specialized chemical interactions can occur, rather than an actual structure.

axon terminal = synaptic end bulb - The swollen or knob-like distal endings to the terminal branches of axons (and axon collaterals) which house the secretory components of the neuron; the site of synthesis, packaging, storage and release of neurotransmitter molecules.

"Exam 3 Review: Chapter 09: Motor Unit and Neuromuscular Junctionmotor neuron - The type of neuron whose cell body is located in the brain or spinal cord, and whose axon runs along a peripheral nerve to synapse with an individual effector cell or group of cells to stimulate the effector into action (contraction or secretion); somatic motor neurons innervate skeletal muscle and activate contraction of a group of skeletal muscle cells, i.e., a motor unit; visceral or autonomic motor neurons innervate visceral effectors, i.e., smooth muscle, cardiac muscle, endocrine glands or exocrine glands.motor unit - The functional unit of a skeletal muscle (organ), composed a voluntary motor neuron and the one or more skeletal muscle fibers which it innervates; muscles with large ratio motor units (1 neuron: many muscle fibers) can provide powerful contractions but cannot provide delicate control for precision movements while muscles with small ratio motor units (1 neuron: few muscle fibers) do not typically provide powerful contractions but can provide delicate control for very precise movements.action potential = nerve impulse - A momentary change in electrical voltage potential (a wave of depolarization) due to the opening of gated sodium channels on the surface of a nerve or muscle cell or gland cell which takes place when the cell is stimulated at or above its threshold level; the all-or-none action potential is capable of transmitting information (inhibition or excitation) to the next cell (s) in the communication pathway.depolarization - The change in membrane voltage potential which triggers the action potential or nerve impulse; the change is due to the opening of gated Na + channels which allow Na + ions to enter the cell cytoplasm causing the resting potential of -70 m V to change to +30 m V in the cell interior.axon - The usually long process of a nerve fiber that conducts impulses (action potentials) away from the cell body of the nerve cell and to the next cell in the control pathway.

synaptic vesicle - Small membranous containers for neurotransmitter substances which are formed by a Golgi apparatus and deliver the neurotransmitter into the synaptic cleft by a process of exocytosis.neurotransmitter - A chemical substance, e.g., acetylcholine, dopamine, etc., a signal molecule which is released from the presynaptic neuron's axon end bulbs upon the arrival of an action potential/nerve impulse to transmit a stimulus across the synapse by exocytosis and diffusion and then binding to a receptor site on a chemically gated ion channel, opening those channels; the influence of this stimulus on the postsynaptic cell may be excitatory or inhibitory.acetylcholine (ACh) - The peripheral excitatory neurotransmitter released at the neuromuscular junction and responsible for stimulating skeletal muscle cells to contract; ACh also serves as a neurotransmitter in the periphery in the autonomic nervous system and in the central nervous system.motor end plate - The area on the sarcolemma within the synapse which contains acetyl choline receptors and various gated ion channels and which contains the enzyme cholinesterase which can catabolize the neurotransmitter, acetyl choline; the binding of acetyl choline (released from the motor neuron's axon terminal bulb) to the gated Na + channels initiates depolarization of the sarcolemma at this postsynaptic communication point (the motor end plate).acetylcholine receptor - An integral membrane protein which is a gated Na + channel which opens in response to the reversible binding of the neurotransmitter acetylcholine; this receptor is located in the post-synaptic cell membranes of skeletal muscle cells, cardiac muscle cells, some smooth muscle cells, some glandular cells, all autonomic postganglionic cells, and a variety of of CNS neurons.acetylcholinesterase - The enzyme located at the motor end plate which breaks down the neurotransmitter acetyl choline in the synapse and which is responsible for stimulating terminating the stimulation of the skeletal muscle cell to make it contract.neuromuscular junction = myoneural junction - The junction or connection, the synapse between the end bulbs of the axon terminals of a somatic motor nerve fiber and the skeletal muscle cell (s) it stimulates to contract using acetyl choline as the excitatory neurotransmitter to open the chemically-gated Na + channels to depolarize the sarcolemma; the location for the beginning (excitation) of excitation-coupling of muscle contraction.synapse = synaptic cleft - The junction, space, cleft or gap across which a nerve impulse passes through the action of a neurotransmitter released from an axon terminal to stimulate the next excitable cell in the pathway, either another neuron, or a muscle cell or gland cell; transmission may be by an electrochemical depolarization event or by release of neurotransmitter molecules into the space.

Describe: (or you may sketch and label)4. The depolarization of a cell membrane. [Note: Depolarization is a part of a larger process which includes the starting point, the resting state, followed by depolarization, repolarization, hyperpolarization, and a return to the resting state.

See Chapter 11 for more details.]I. Resting state: a) all voltage-gated and chemically-gated ion channels are closed b) membrane potential approximately -70 m V c) the Na + K + ATPase pumps are operating (3 Na + out/2 K + in per ATP hydrolysis)II.

Depolarization phase: a) a stimulus of threshold strength or greater causes the gated Na + ion channels to open; Na + ions diffuse into the cytoplasm b) membrane potential reverses from approximately -70 m V to approximately +30 m V c) the Na + K + ATPase pumps are operating (3 Na + out/2 K + in per ATP hydrolysis)III.

Repolarization phase: a) the gated Na + ion channels slowly close; Na + ions can no longer diffuse into the cytoplasm b) meanwhile, the gated K + ion channels open; K + ions diffuse out of the cytoplasm c) membrane potential reverses again, dropping from approximately +30 m V to approximately -70 m V d) the Na + K + ATPase pumps are operating (3 Na + out/2 K + in per ATP hydrolysis)IV.

Hyperpolarization phase: a) the gated Na + ion channels have closed; Na + ions can no longer diffuse into the cytoplasm b) meanwhile, the gated K + ion channels slowly close; K + ions can no longer diffuse out of the cytoplasm c) membrane potential becomes more negative than the resting state, dropping to approximately -80 m V d) the Na + K + ATPase pumps are operating (3 Na + out/2 K + in per ATP hydrolysis) and will restore the resting state conditions Sketch and Label:1. A ""motor unit.""2. the cellular and molecular compnennts of a neuromuscular junction. "

The portion of the neuron that sends signals. Axons are long tail-like extensions protruding from the cell body. The axon terminal is the knob-like structure at the far end of the axon.

Nerve cells and neuronal communication Flashcards

Terms Definitions Neuron Nerve cell specialised for communication The cell body Also called the soma is the central region of the neuron. Materials needed by the neuron are made here. Dendrite Portion of the neuron that receives signals. They are branchlike extensions for receiving information from other neurons Axon

Synaptic vesicles Spherical sac containing neurotransmitters. They are found in the axon terminal. They are manufactured in the cell body and travel down the length of the axon. When the synaptic vesicles reaches the end on the axon terminal it bursts, releasing neurotransmitters Neurotransmitter Chemical messenger specialised for communication from neuron to neuron.

Synapse Space between two connecting neurons through which messages are transmitted chemically. Glial cells Cell in nervous system that plays a role I the formation of myelin and the blood-brain barrier, responds to injury, removes debris and enhances learning and memory Myelin sheath Glial cells wrapped around axons that act as insulators of the neuron's signal.

Resting potential Electrical charge difference (-60 millivolts) across the neuronal membrane, when the neuron is not being stimulated or inhibited.

Action potential Electrical impulse that travels down the axon triggering the release of neurotransmitters. Positively charged particles flow rapidly into the axon then just as rapidly flow out. These sudden shifts in charge produce a release of electricity. When the electrical charge reaches the axon terminal it triggers the release of neurotransmitters into the synapse.

Absolute refractory period Time during which another action potential is impossible; limits maximal firing rate (fastest rate at which a neuron can fire)Receptor site Location that uniquely recognises a neurotransmitter. Think of a neurotransmitter as a key and the receptor site as the lock Reuptake Means of recycling neurotransmitters. A process by which synaptic vesicle reabsorbs the neurotransmitter. Neural plasticity Ability of the brain and the nervous system to change

y Answers.com ® is making the world better one answer at a time. At the distal end, and axon usually has a terminal arborization (Telodendria)- and extensive complex of fine branches. Each branch ends in a synaptic knob (Terminal button), a little swelling that forms a junction (synapse) with the next cell. It contains synaptic vesicles full of neurotransmitters.

What is the function of an telodendria in a neuron?

Answers.com ® Wiki Answers ® Categories Science Biology Human Anatomy and Physiology Nervous System Nerves What is the function of an telodendria in a neuron? Flag What is the function of an telodendria in a neuron? Answered by The Wiki Answers ®Communit

4 people found this useful Was this answer useful? Yes Somewhat No What is the function of a neuron? The function Of a neuron is to transmit a signal at a very fast rate. Julieyumi 2,972 Contributions Functions of a neuron?

It's a brain cell that receives afferent (sensory) information and/or sends efferent (motor) information via action potentials and neurotransmitters. Jazz M 28,354 Contributions A veterinarian with a love of animals, history and tea. What is the function of the association neuron? Association neurons, also known as interneurons, connect sensory (afferent) neurons to motor (efferent) neurons.

Dendrites function in the motor neuron? To carry the nerve impulse from the CNS to the cell body What is the function of the nucleus in a neuron?

The nucleus function in all animal cells is mostly the same. Nuclei carry genetic material and are responsible for cell division. What is the function of neuron? The function of a neuron is to transfer messages throughout the brain. These neurons are all attached and interpret everything that happens. What is the function of the neuron?

A neuron is the basic unit of structure and function in the nervous system. The neurons function is to conduct electrochemical impulses. The Medieval Jester 291 Contributions What is the Function of Neurons? Sensory neurons relay information from sense organs, motor neurons carry impulses to muscles and glands, and inter-neurons transmit impulses between sensory and motor neurons. …What is the function of the neurons?neurons are the function units of the nervous system. they transmit signals from one cell to another via electrical excitability.

essentially they transmit nerve impulses. What are the function of neurons?the function of neurons is to receive information, process it, and pass it on to other neurons, or muscles or endocrine/exocrine glands.

I realize 'receive information, proces …What is a telodendria? Any of the terminal or smaller branches of an axon that terminates with specialized ending that releases neurotransmitters. Soalric Parker 283 Contributions The functions of neurons? Neurons make up our brains. They send electric pulses to each other to communicate thoughts.

Llpurpleflame 10 Contributions Answered In Neuroscience What are the functions of the neurons? Neurons convert stimuli into electrical signals called action potentials and conduct these action potentials to other neurons, muscle tissue or to glands Taken from the 12th e …Answered In Biology What is a neuron and what is its function? Neurons carry information throughout the body. It is a cell Answered In Neuroscience What is the function of telodendria?

The main function of the telodendria is to store vesicles that contain neurotransmitters. It then releases the neurotransmitters so neurons can communicate with one anothe …Jim west70 17,544 Contributions Answered In Nerves What are functions of the neurons? A neuron (pronounced /ˈnjʊərɒn/ N (Y)OOR-on, also known as a neurone or nerve cell) is an electrically excitable cell that processes and transmits information by electrical …Answered In Human Anatomy and Physiology What is the function of the neuronal membrane in a neuron? Gwapo ko By: Michael Vincent T. Valencia

ers A chemical that is released into the synaptic cleft from the axon terminal of a sending neuron, crosses a synapse, and binds to appropriate receptor sites on the dendrites or cell body of a receiving neuron, influencing the cell either to fire or not to fire

Notes Biological Foundations of Behavior Neurons Anatomy of a Neuron Cell body The part of the neuron that contains the nucleus and carries out the neuron’s metabolic functions Dendrites The branchlike extensions of a neuron that receive signals from other neurons Axon The slender, tail-like extension of the neuron that transmits signals to the dendrites or cell body of the other neurons or to muscles or glands Glial cells Cells that help to make the brain more efficient by holding neurons together, removing waste products such as dead neurons, making the myelin coating for the axons, and performing other manufacturing, nourishing, and cleanup tasks Synapse The junction where the axon of a sending neuron communicates with a receiving neuron across the synaptic cleft Permeability The capability of being penetrated or passed through Resting potential The membrane potential of a neuron at rest, about 270 millivolts Action potential The sudden reversal of the resting potential, which initiates the firing of a neuron Difference between a strong and weak stimulus A weak stimulus may cause few neurons to fire and at a slow rate A strong stimulus my cause thousands of neurons to fire at the same time and at hundreds of times per second Myelin sheath The white, fatty coating wrapped around some axons that acts as insulation and enables impulses to travel much faster Multiple sclerosis involves deterioration of the myelin sheath Neurotransmitt

Receptors Protein molecules on the dendrite or cell body of a neuron that will interact only with specific neurotransmitters Action of Neurotransmitters Excitatory Influencing the neurons to fire Inhibitory Influencing them not to fire How synaptic vesicles can continually pour out neurotransmitters Cell body of the neuron is always working to manufacture more of the neurotransmitter substance Unused neurotransmitters in the synaptic cleft may be broken down into their component molecules and reclaimed by the axon terminal to be recycled and used again Reuptake The process by which neurotransmitter molecules are taken from the synaptic cleft back into the axon terminal for later use, thus terminating their excitatory or inhibitory effect on the receiving neuron Neurotransmitterso Acetylcholine· A neurotransmitter that plays a role in learning, memory, and rapid eye movement (REM) sleep and causes the skeletal muscle fibers to contracto Glutamate· Primary excitatory neurotransmitter in the braino GABA· Main inhibitory neurotransmitter in the brain Neurotransmitters called monoamines Dopamine A neurotransmitter that plays a role in learning, attention, and movement Norepinephrine A neurotransmitter affecting eating and sleep Epinephrine A neurotransmitter that affects the metabolism of glucose and energy stored in muscles to be released during exercise Serotonin A neurotransmitter that plays an important role in regulating mood, sleep, aggression, and appetite Endorphins Chemicals produced naturally by the brain that reduce pain and positively affect mood“Runner’s high” is attributed to the release of endorphins Candace Pert and her fellow researchers Demonstrated that a localized region of the brain contains neurons with receptors that respond to the opiates The brain produces opiate like substances known as endorphins Nervous System Central Nervous System The brain and the spinal cord Peripheral nervous system Connects the central nervous system to all other parts of the body Central Nervous System Spinal cord An extension of the brain, reaching form the base of the brain through the neck and spinal column, that transmits messages between the brain and the peripheral nervous system Protected by bone and spinal fluid Brain structures Hindbrain (Brainstem)Midbrain Forebrain Hindbrain Brainstem The structure that begins at the point where the spinal cord enlarges as it enters the brain Medulla The part of the brainstem that controls heartbeat, blood pressure, breathing, coughing, and swallowing Reticular formation A structure in the brainstem that plays a crucial role in arousal and attention and that screens sensory messages entering the brain Pons A structure in the brainstem that plays a role in body movement and even exerts an influence on sleep and dreaming Cerebellum The brain structure that executes smooth, skilled body movements and regulates muscle tone and posture Midbraino The structures of this brain region act primarily as relay stations through which the basic physiological functions of the hindbrain are linked to the cognitive functions of the forebrain Substantia nigra The midbrain structure that controls unconscious motor movements Thalamus The structure, located above the brainstem, that acts as a relay station for information flowing into or out of the higher brain centers Regulates sleep cycles Hypothalamus A small but influential brain structure that controls the pituitary gland and regulates hunger, thirst, sexual behavior, body temperature, and a vide variety of emotional behaviors Limbic system A group of structures in the brain, including the amygdala and hippocampus, that are collectively involved in emotion, memory and motivation Amygdala A structure in the limbic system that plays an important role in emotion, particularly in response to aversive stimuli Hippocampus A structure in the limbic system that plays a central role in the formation of long-term memories Forebrain Cerebrum The largest structure of the human brain, consisting of the two cerebral hemispheres connected by the corpus callosum and covered by the cerebral cortex Cerebral hemispheres The right and left halves of the cerebrum, covered by the cerebral cortex and connected by the corpus callosum Corpus callosum The thick band of nerve fibers that connects the two cerebral hemispheres and make possible the transfer of information and the synchronization of activity between them Cerebral cortex The gray, convoluted covering of the cerebral hemispheres that is responsible for higher mental processes such as language, memory, and thinking Referred to as gray matter Andreason and others Indicated that the amount of gray matter is positively correlated with human intelligence Convolutions The numerous folds or wrinkles in the cortex Three types of areas of the cerebral cortex Sensory input areas: where vision, hearing, tough, pressure, and temperature register Motor areas: which control voluntary movement Association areas: which house memories and are involved in though, perception, and language Four Lobes of Cerebrum Frontal lobes The lobes that control voluntary body movements, speech production, and such functions as thinking, motivation, planning for the future, impulse control, and emotional responses Contains the motor cortex, Broca’s area, and the frontal association areas Motor Cortex The strip of tissue at the rear of the frontal lobes that controls voluntary body movement Discovered by Fritsch and Hitzig Wilder Penfield Applied electrical stimulation to the motor cortex of conscious human patients undergoing neurosurgery Mapped the primary motor cortex in humans Plasticity is maintained throughout life The capacity of the brain to adapt to changes such as brain damage Broca’s area The area in the frontal lobe, usually in the left hemisphere, that controls the production of speech sounds Paul Broca Among the first scientists to demonstrate the existence of localized functions in the cerebral cortex and concluded that the site of damage was the part of the brain responsible for speech production Broca’s aphasia An impairment in the physical ability to produce speech sounds, or in extreme cases an inability to speak at all Aphasia A loss or impairment of the ability to understand or communicate through the written or spoken word, which results from damage to the brain Frontal Association Areas Consists of association areas involved in thinking, motivation, planning for the future, impulse control, and emotional responses Parietal lobes The lobes that contain the somatosensory cortex and other areas that are responsible for body awareness and spatial orientation Somatosensory cortex The strip of tissue at the front of the parietal lobe where touch, pressure, temperature, and pain register in the cerebral cortex Occipital lobes The lobes that contain the primary visual cortex and association areas involved in the interpretation of visual information Primary visual cortex The area at the rear of the occipital lobes where vision registers in the cerebral cortex Each eye is connected the primary visual cortex in both right and left occipital lobes Temporal lobes The lobes that contain the primary auditory cortex, Wernicke’s area, and association areas for interpreting auditory information Primary auditory cortex The part of the temporal lobes where hearing registers in the cerebral cortex Wernicke’s area The language area in the temporal lobe involved in comprehension of the spoken work and in formulation of coherent speech and written language Wernicke’s aphasia Aphasia that results from damage to Wernicke’s area and in which the person’s spoken language is fluent, but the content is either vague or incomprehensible to the listener Another kind of aphasia is auditory aphasia Word deafness Temporal association areas House memories and are involved in the interpretation of auditory stimuli There is a special association area where familiar melodies are stored Cerebral Hemisphereso Left hemisphere· The hemisphere that controls the right side of the body, coordinates complex movements, and in 95% of right-handers and 62% of left-handers, controls most functions of speech and written languageo Right hemisphere· The hemisphere that controls the left side of the body and that, in most people, is specialized for visual-spatial perception and for interpreting nonverbal behavioro Unilateral neglect· Patients with right hemisphere damage that may have attention deficits and be unaware of objects in the left visual field Right hemisphere’s role in emotion The right hemisphere is involved in our expression of emotion through tone of voice and facial expressions Controls the left side of the face and usually conveys stronger emotion than the right side of the face Lawrence Miller Describes the facial expressions and the voice inflection of people with right hemisphere damage as “often strangely blank –almost robotic”Split brain Split-brain operation An operation in which the corpus callosum is cut, separating the cerebral hemispheres and usually lessening the severity and frequency of grand mal seizures Joseph Bogen and Philip Vogel Found that patients with severe epilepsy could be helped by surgery that severed their corpus callosum rendering communication between the two hemispheres impossible Roger Sperry and Michael Gazzaniga and Jerre Levy Their research with split-brain patients has expanded knowledge of the unique capabilities of the individual hemispheres Roger Sperry Found that when the brain was surgically separated, each hemisphere continued to have individual and private experiences, sensations, thoughts, and perceptions Roger Sperry 1981 Nobel Prize research The right hemisphere knows and remembers what it sees just as well as the left, but unlike the left hemisphere, the right cannot name what it has seen Handedness Corpus callosum of left-handers is 11% larger and contains up to 2.5 million more nerve fibers than that of right-handers In general, the two sides of the brain are less specialized in left-handers Left-handers tend to experience less language loss following an injury to either hemisphere Left-handers tend to have higher rates of learning disabilities and mental disorders than right-handers Studies of ancient populations show that the proportions of left- and right-handers in the human population has been about the same for several thousand years Hepper and others Of the human fetuses they observed, 94.6%were sucking their right thumb and only 5.4% were sucking their left thumb Machines that Measure Brain Activity Electroencephalogram Hans Berger Invented the electroencephalograph, a machine that amplifies a million times the electrical activity occurring in the brain A record of brain-wave activity made by the electroencephalograph Beta wave The brain wave associated with mental or physical activity Alpha wave The brain wave associated with deep relaxation Delta wave The brain wave associated with slow-wave (deep) sleep Microelectrode An electrical wire So small that it can be inserted near or into a single neuron without damaging it Can be used to monitor the electrical activity of a single neuron or to stimulate activity within it Used to discover the exact functions of single cells within the primary visual cortex and the primary auditory cortex CT scan (computerized axial tomography)A brain-scanning technique involving a rotating X-ray scanner and a high-speed computer analysis that produces slice-by-slice, cross-sectional images of the structure of the brain MRI (magnetic resonance imagery)A diagnostic scanning technique that produces high-resolution images of the structures of the brain PET scan (positron-emission tomography)A diagnostic scanning technique that produces high-resolution images of the structures of the brain Functional MRI (f MRI)A brain-imaging technique that reveals both brain structure and brain activity SQUID (superconducting quantum interference device)Images brain activity by measuring magnetic changes produced by the electric current neurons discharge when they fire MEG (magnetoencephalography)Measures magnetic changes produced by the electrical activity from firing neurons and can also image neural activity within the brain as rapidly as it occurs, much faster than PET or f MRIBrain Across the Lifespan Synaptogenesis Process where synapses develop as a result of growth of both dendrites and axons Pruning The process through which the developing brain eliminates unnecessary or redundant synapses Myelination The development of myelin sheaths around axons, begins prior to birth but continues well into adulthood Hemispheric specialization Language processing occurs primarily in the left hemisphere Spatial perception is not lateralized until around the age of 8Plasticity The ability of the brain to reorganized, to reshape itself in response to input from both internal and external sources, and to compensate for damage Aging Brain weight begins to decline around age 30Gray matter, but not white matter, is lost with normal aging in both hemispheres of the cerebellum Exposure to patterned auditory stimuli, such as that which is characteristic of human language, may be particularly important to the development of the primary auditory cortex in young children Stroke The most common cause of damage to adult brains, arising when blockage of an artery cuts off the blood supply to a particular area of the brain or when a blood vessel bursts A high percentage of stroke survivors suffer from depression Patients who receive TPA (a blood clot-dissolving drug) within 3 hours of the onset of a stroke are 30% more likely to have minimal or no disability Peripheral nervous system (PNS)o The nerves connecting the central nervous system to the rest of the bodyo Contains two subdivisions· Somatic Division· Autonomic Division – contains two divisions§ Sympathetic Division (Activates)§ Parasympathetic Division (Inhibits)o Somatic Division· Consists of all the sensory nerves, which transmit information from the sense receptors-eyes, ears, nose, tongue, and skin-to the central nervous system· Consists of all the motor nerves, which relay messages from the central nervous system to all the skeletal muscles of the bodyo Autonomic Division· Operates without any conscious control or awareness on your part· Transmits messages between the central nervous system and the glands, the cardiac muscle, and the smooth muscles· Divided into two parts§ Sympathetic nervous system· Mobilizes the body’s resources during stress, emergencies, or heavy exertion, preparing the body for action· Named the fight-or-flight response by Walter Cannon§ Parasympathetic nervous system· Associated with relaxation and the conservation of energy.

The division that brings the heightened bodily responses back to normal following an emergency. Endocrine Systemo A system of ductless glands in various parts of the body that manufacture and secrete hormones into the bloodstream or lymph fluids, thus affecting cells in other parts of the bodyo Hormones· A substance manufactured and released in one part of the body that affects other parts of the bodyo Pituitary gland· The endocrine gland located in the brain and often called the “master gland,” which releases hormones that control other endocrine glands and also releases a growth hormone· Releases the hormones that activate the other glands in the endocrine systemo Thyroid gland· Produces the important hormone thyroxin, which regulates the rate at which food is metabolizedo Pancreas· Regulates the body’s blood sugar levels by releasing the hormones insulin and glucagon into the bloodstreamo Adrenal glands· A pair of endocrine glands that release hormones that prepare the body for emergencies and stressful situations and also release small amounts of the sex hormoneso Gonads· Sex glands – the ovaries in females and the testes in males· Release the sex hormones that make reproduction possible and that are responsible for the secondary sex characteristics Genes and Behavioral Geneticso Genes· The segments of DNA that are located on the chromosomes and are the basic units for the transmission of all hereditary traitso Chromosomes· Rod-shaped structures in the nuclei of body cells, which contain all the genes and carry all the hereditary informationo Zygote· A single cell formed from the union of 23 chromosomes from the male’s sperm and 23 chromosomes from the female’s eggo Chromosomes· Autosomes· Matching pairs of chromosomes· 22 of the 23 pairs of chromosomes are autosomeso Sex chromosomes· The 23rd pair of chromosomes that carry the genes that determine a person’s sex· Sex chromosomes of females consist of two X’s (XX)· Sex chromosomes of males consist of one X and one Y (XY)o Dominant-recessive pattern· A pattern of inheritance in which the presence of a single dominant gene causes a trait to be expressed, and two genes are required for the expression of a recessive trait· Heterozygous§ A person who carries two copies of the same gene· Homozygous§ A person who carries two different geneso Polygenic inheritance· Many genes influence a particular characteristico Multi-factorial· A pattern of inheritance in which a trait is influenced by several genes as well as environmental factorso Sex-linked inheritance· Involves the genes on the X and Y chromosomes· In females the harmful gene is offset by the gene that is not harmful· In males if the single X chromosome carries a harmful gene, there is no offsetting gene on the Y chromosome because it is very small and carries only the genes needed to create the male body typeo Behavioral genetics· A field of research that investigates the relative effects of heredity and environment on behavior ability· Found that genes clearly contribute to individual difference in both intelligence and personality· Also found that environmental factors influence these characteristics as well Genes and Behavioral Geneticso Genes· The segments of DNA that are located on the chromosomes and are the basic units for the transmission of all hereditary traitso Chromosomes· Rod-shaped structures in the nuclei of body cells, which contain all the genes and carry all the hereditary informationo Zygote· A single cell formed from the union of 23 chromosomes from the male’s sperm and 23 chromosomes from the female’s eggo Chromosomes· Autosomes· Matching pairs of chromosomes· 22 of the 23 pairs of chromosomes are autosomeso Sex chromosomes· The 23rd pair of chromosomes that carry the genes that determine a person’s sex· Sex chromosomes of females consist of two X’s (XX)· Sex chromosomes of males consist of one X and one Y (XY)o Dominant-recessive pattern· A pattern of inheritance in which the presence of a single dominant gene causes a trait to be expressed, and two genes are required for the expression of a recessive trait· Heterozygous§ A person who carries two copies of the same gene· Homozygous§ A person who carries two different geneso Polygenic inheritance· Many genes influence a particular characteristico Multi-factorial· A pattern of inheritance in which a trait is influenced by several genes as well as environmental factorso Sex-linked inheritance· Involves the genes on the X and Y chromosomes· In females the harmful gene is offset by the gene that is not harmful· In males if the single X chromosome carries a harmful gene, there is no offsetting gene on the Y chromosome because it is very small and carries only the genes needed to create the male body typeo Behavioral genetics· A field of research that investigates the relative effects of heredity and environment on behavior ability· Found that genes clearly contribute to individual difference in both intelligence and personality· Also found that environmental factors influence these characteristics as well Created with Microsoft Office One Note 2003 One place for all your notes

Most axons carry signals in the form of action potentials, which are discrete electrochemical impulses that travel rapidly along an axon, starting at the cell body and terminating at points where the axon makes synaptic contact with target cells.

Axon

"From Wikipedia, the free encyclopedianavigation search For other uses, see Axon (disambiguation). Axon An axon of a multipolar neuron Identifiers Me SH D001369Anatomical terminology [ edit on Wikidata]An axon (from Greek ἄξων áxōn, axis) or nerve fiber, is a long, slender projection of a nerve cell, or neuron, that typically conducts electrical impulses known as action potentials, away from the nerve cell body.

The function of the axon is to transmit information to different neurons, muscles, and glands. In certain sensory neurons ( pseudounipolar neurons ), such as those for touch and warmth, the axons are called afferent nerve fibers and the electrical impulse travels along these from the periphery to the cell body, and from the cell body to the spinal cord along another branch of the same axon.

Axon dysfunction has caused many inherited and acquired neurological disorders which can affect both the peripheral and central neurons. Nerve fibers are classed into three types – group A nerve fibers, group B nerve fibers, and group C nerve fibers. Groups A and B are myelinated, and group C are unmyelinated. These groups include both sensory fibers and motor fibers.

Another classification, groups only the sensory fibers, and these are grouped as Type I, Type II, Type III, and Type IV.

An axon is one of two types of cytoplasmic protrusions from the cell body of a neuron; the other type is a dendrite. Axons are distinguished from dendrites by several features, including shape (dendrites often taper while axons usually maintain a constant radius), length (dendrites are restricted to a small region around the cell body while axons can be much longer), and function (dendrites receive signals whereas axons transmit them).

Some types of neurons have no axon and transmit signals from their dendrites. No neuron ever has more than one axon; however in invertebrates such as insects or leeches the axon sometimes consists of several regions that function more or less independently of each other.

[1]Axons are covered by a membrane known as an axolemma; the cytoplasm of an axon is called axoplasm. Most axons branch, in some cases very profusely. The end branches of an axon are called telodendria. The swollen end of a telodendron is known as the axon terminal which joins the dendron or cell body of another neuron forming a synaptic connection.

Axons make contact with other cells—usually other neurons but sometimes muscle or gland cells—at junctions called synapses. In some circumstances, the axon of one neuron may form a synapse with the dendrites of the same neuron, resulting in an autapse.

At a synapse, the membrane of the axon closely adjoins the membrane of the target cell, and special molecular structures serve to transmit electrical or electrochemical signals across the gap. Some synaptic junctions appear along the length of an axon as it extends—these are called en passant (""in passing"") synapses and can be in the hundreds or even the thousands along one axon.

[2] Other synapses appear as terminals at the ends of axonal branches. A single axon, with all its branches taken together, can innervate multiple parts of the brain and generate thousands of synaptic terminals. A bundle of axons make a nerve tract in the central nervous system, [3] and a fascicle in the peripheral nervous system.

The largest white matter tract in the brain is the corpus callosum formed of some 20 million axons.

[3]Contents [ hide ]1 Anatomy1.1 Axonal region1.1.1 Axon hillock1.1.2 Initial segment1.2 Axonal transport1.3 Myelination1.4 Nodes of Ranvier1.5 Axon terminals2 Action potentials3 Development and growth3.1 Development3.1.1 Extracellular signaling3.1.2 Intracellular signaling3.1.3 Cytoskeletal dynamics3.2 Growth4 Classification4.1 Motor4.2 Sensory4.3 Autonomic5 Clinical significance6 History7 Other animals8 See also9 References10 External links Anatomy [ edit]A typical myelinated axon A dissected human brain, showing grey matter and white matter Axons are the primary transmission lines of the nervous system, and as bundles they form nerves.

Some axons can extend up to one meter or more while others extend as little as one millimeter. The longest axons in the human body are those of the sciatic nerve, which run from the base of the spinal cord to the big toe of each foot. The diameter of axons is also variable. Most individual axons are microscopic in diameter (typically about one micrometer (µm) across). The largest mammalian axons can reach a diameter of up to 20 µm. The squid giant axon, which is specialized to conduct signals very rapidly, is close to 1 millimetre in diameter, the size of a small pencil lead.

The numbers of axonal telodendria (the branching structures at the end of the axon) can also differ from one nerve fiber to the next.

Axons in the central nervous system (CNS) typically show multiple telodendria, with many synaptic end points. In comparison, the cerebellar granule cell axon is characterized by a single T-shaped branch node from which two parallel fibers extend.

Elaborate branching allows for the simultaneous transmission of messages to a large number of target neurons within a single region of the brain. There are two types of axons in the nervous system: myelinated and unmyelinated axons. [4] Myelin is a layer of a fatty insulating substance, which is formed by two types of glial cells Schwann cells and oligodendrocytes. In the peripheral nervous system Schwann cells form the myelin sheath of a myelinated axon. In the central nervous system oligodendrocytes form the insulating myelin.

Along myelinated nerve fibers, gaps in the myelin sheath known as nodes of Ranvier occur at evenly spaced intervals. The myelination enables an especially rapid mode of electrical impulse propagation called saltatory conduction. The myelinated axons from the cortical neurons form the bulk of the neural tissue called white matter in the brain.

The myelin gives the white appearance to the tissue in contrast to the grey matter of the cerebral cortex which contains the neuronal cell bodies. A similar arrangement is seen in the cerebellum. Bundles of myelinated axons make up the nerve tracts in the CNS. Where these tracts cross the midline of the brain to connect opposite regions they are called commissures. The largest of these is the corpus callosum that connects the two cerebral hemispheres, and this has around 20 million axons.

[3]The structure of a neuron is seen to consist of two separate functional regions, or compartments – the cell body together with the dendrites as one region, and the axonal region as the other. [2] Nissl bodies of the soma and dendrites, where protein is synthesised is absent in the axonal region which includes the axon hillock. [2]Axonal region [ edit]The axonal region or compartment, includes the axon hillock, the initial segment, the rest of the axon, and the axon telodendria, and axon terminals.

It also includes the myelin sheath. The Nissl bodies that produce the neuronal proteins are absent in the axonal region. [2] Proteins needed for the growth of the axon, and the removal of waste materials, need a framework for transport.

This axonal transport is provided for in the axoplasm. Axon hillock [ edit]Detail showing microtubules at axon hillock and initial segment. The axon hillock is the area formed from the cell body of the neuron as it extends to become the axon.

It precedes the initial segment. The received action potentials that are summed in the neuron are transmitted to the axon hillock for the generation of an action potential from the initial segment.

Initial segment [ edit]The axon initial segment — the thick, unmyelinated part of an axon that connects directly to the cell body — consists of a specialized complex of proteins. It is approximately 25 µm in length and functions as the site of action potential initiation. [5] The density of voltage-gated sodium channels is much higher in the initial segment than in the remainder of the axon or in the adjacent cell body, excepting the axon hillock.

[6] The voltage-gated ion channels are known to be found within certain areas of the axonal membrane and initiate action potential, conduction, and synaptic transmission.

[4]Axonal transport [ edit]Main article: Axonal transport The axoplasm is the equivalent of cytoplasm in the cell. Microtubules form in the axoplasm at the axon hillock. They are arranged along the length of the axon, in overlapping sections, and all point in the same direction – towards the axon terminals.

[7] This is noted by the positive endings of the microtubules. This overlapping arrangement provides the routes for the transport of different materials from the cell body.

[7] Studies on the axoplasm has shown the movement of numerous vesicles of all sizes to be seen along cytoskeletal filaments – the microtubules, and neurofilaments, in both directions between the axon and its terminals and the cell body. Outgoing anterograde transport from the cell body along the axon, carries mitochondria and membrane proteins needed for growth to the axon terminal.

Ingoing retrograde transport carries cell waste materials from the axon terminal to the cell body. [8] Outgoing and ingoing tracks use different sets of motor proteins. [7] Outgoing transport is provided by kinesin, and ingoing return traffic is provided by dynein.

Dynein is minus-end directed. [8] There are many forms of kinesis and dynein motor proteins, and each is thought to carry a different cargo.

[7] The studies on transport in the axon led to the naming of kinesin. [7]Myelination [ edit]Transmission electron micrograph of a myelinated axon in cross-section. Generated by the electron microscopy unit at Trinity College, Hartford CTCross section of an axon. 1. Axon 2. Nucleus of Schwann cell 3. Schwann cell 4. Myelin sheath 5. Neurilemma In the nervous system, axons may be myelinated, or unmyelinated. This is the provision of an insulating layer, called a myelin sheath. In the peripheral nervous system axons are myelinated by glial cells known as Schwann cells.

In the central nervous system the myelin sheath is provided by another type of glial cell, the oligodendrocyte. Schwann cells myelinate a single axon. An oligodendrocyte can myelinate up to 50 axons. [9]Nodes of Ranvier [ edit]Main article: Node of Ranvier Nodes of Ranvier (also known as myelin sheath gaps) are short unmyelinated segments of a myelinated axon, which are found periodically interspersed between segments of the myelin sheath.

Therefore, at the point of the node of Ranvier, the axon is reduced in diameter. [10] These nodes are areas where action potentials can be generated.

In saltatory conduction, electrical currents produced at each node of Ranvier are conducted with little attenuation to the next node in line, where they remain strong enough to generate another action potential. Thus in a myelinated axon, action potentials effectively ""jump"" from node to node, bypassing the myelinated stretches in between, resulting in a propagation speed much faster than even the fastest unmyelinated axon can sustain.

Axon terminals [ edit]An axon can divide into many branches called telodendria (Greek–end of tree). At the end of each telodendron is an axon terminal (also called a synaptic bouton, or terminal bouton). Axon terminals contain synaptic vesicles that store the neurotransmitter for release at the synapse. This makes multiple synaptic connections with other neurons possible. Sometimes the axon of a neuron may synapse onto dendrites of the same neuron, when it is known as an autapse. Action potentials [ edit]Main article: Action potential Further information: Neural coding Structure of a typical chemical synapse Postsynaptic density Voltage- gated Ca ++ channel Synaptic vesicle Neurotransmitter transporter Receptor Neurotransmitter Axon terminal Synaptic cleft Dendrite

Most axons carry signals in the form of action potentials, which are discrete electrochemical impulses that travel rapidly along an axon, starting at the cell body and terminating at points where the axon makes synaptic contact with target cells.

The defining characteristic of an action potential is that it is ""all-or-nothing"" — every action potential that an axon generates has essentially the same size and shape. This all-or-nothing characteristic allows action potentials to be transmitted from one end of a long axon to the other without any reduction in size. There are, however, some types of neurons with short axons that carry graded electrochemical signals, of variable amplitude.

When an action potential reaches a presynaptic terminal, it activates the synaptic transmission process. The first step is rapid opening of calcium ion channels in the membrane of the axon, allowing calcium ions to flow inward across the membrane.

The resulting increase in intracellular calcium concentration causes synaptic vesicles (tiny containers enclosed by a lipid membrane) filled with a neurotransmitter chemical to fuse with the axon's membrane and empty their contents into the extracellular space. The neurotransmitter is released from the presynaptic nerve through exocytosis. The neurotransmitter chemical then diffuses across to receptors located on the membrane of the target cell.

The neurotransmitter binds to these receptors and activates them. Depending on the type of receptors that are activated, the effect on the target cell can be to excite the target cell, inhibit it, or alter its metabolism in some way.

This entire sequence of events often takes place in less than a thousandth of a second. Afterward, inside the presynaptic terminal, a new set of vesicles is moved into position next to the membrane, ready to be released when the next action potential arrives. The action potential is the final electrical step in the integration of synaptic messages at the scale of the neuron.

[4]A)pyramidal cell, interneuron, and short durationwaveform (Axon). (B) overlay of the three average waveforms; (C) average and standard error of peak-trough time for pyramidal cells interneurons, and putative axons. (D)Scatter plot of signal to noise ratios for individual units againstpeak-trough time for axons, pyramidal cells (PYR) and interneurons (INT). Extracellular recordings of action potential propagation in axons has been demonstrated in freely moving animals.

While extracellular somatic action potentials have been used to study cellular activity in freely moving animals such as place cells, axonal activity in both white and gray matter can also be recorded. Extracellular recordings of axon action potential propagation is distinct from somatic action potentials in three ways: 1.

The signal has a shorter peak-trough duration (~150μs) than of pyramidal cells (~500μs) or interneurons (~250μs). 2. The voltage change is triphasic. 3. Activity recorded on a tetrode is seen on only one of the four recording wires.

In recordings from freely moving rats, axonal signals have been isolated in white matter tracts including the alveus and the corpus callosum as well hippocampal gray matter. [11]In fact, the generation of action potentials in vivo is sequential in nature, and these sequential spikes constitute the digital codes in the neurons.

Although previous studies indicate an axonal origin of a single spike evoked by short-term pulses, physiological signals in vivo trigger the initiation of sequential spikes at the cell bodies of the neurons. [12] [13]In addition to propagating action potentials to axonal terminals, the axon is able to amplify the action potentials, which makes sure a secure propagation of sequential action potentials toward the axonal terminal.

In terms of molecular mechanisms, voltage-gated sodium channels in the axons possess lower threshold and shorter refractory period in response to short-term pulses. [14]Development and growth [ edit]Development [ edit]The development of the axon to its target, is one of the six major stages in the overall development of the nervous system.

[15] Studies done on cultured hippocampal neurons suggest that neurons initially produce multiple neurites that are equivalent, yet only one of these neurites is destined to become the axon. [16] It is unclear whether axon specification precedes axon elongation or vice versa, [17] although recent evidence points to the latter.

If an axon that is not fully developed is cut, the polarity can change and other neurites can potentially become the axon. This alteration of polarity only occurs when the axon is cut at least 10 μm shorter than the other neurites. After the incision is made, the longest neurite will become the future axon and all the other neurites, including the original axon, will turn into dendrites. [18] Imposing an external force on a neurite, causing it to elongate, will make it become an axon.

[19] Nonetheless, axonal development is achieved through a complex interplay between extracellular signaling, intracellular signaling and cytoskeletal dynamics. Extracellular signaling [ edit]The extracellular signals that propagate through the extracellular matrix surrounding neurons play a prominent role in axonal development.

[20] These signaling molecules include proteins, neurotrophic factors, and extracellular matrix and adhesion molecules. Netrin (also known as UNC-6) a secreted protein, functions in axon formation. When the UNC-5 netrin receptor is mutated, several neurites are irregularly projected out of neurons and finally a single axon is extended anteriorly.

[21] [22] [23] [24] The neurotrophic factors – nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NTF3) are also involved in axon development and bind to Trk receptors. [25]The ganglioside -converting enzyme plasma membrane ganglioside sialidase (PMGS), which is involved in the activation of Trk A at the tip of neutrites, is required for the elongation of axons.

PMGS asymmetrically distributes to the tip of the neurite that is destined to become the future axon. [26]Intracellular signaling [ edit]During axonal development, the activity of PI3K is increased at the tip of destined axon.

Disrupting the activity of PI3K inhibits axonal development. Activation of PI3K results in the production of phosphatidylinositol (3,4,5)-trisphosphate (Ptd Ins) which can cause significant elongation of a neurite, converting it into an axon.

As such, the overexpression of phosphatases that dephosphorylate Ptd Ins leads into the failure of polarization. [20]Cytoskeletal dynamics [ edit]The neurite with the lowest actin filament content will become the axon. PGMS concentration and f-actin content are inversely correlated; when PGMS becomes enriched at the tip of a neurite, its f-actin content is substantially decreased.

[26] In addition, exposure to actin-depolimerizing drugs and toxin B (which inactivates Rho-signaling) causes the formation of multiple axons. Consequently, the interruption of the actin network in a growth cone will promote its neurite to become the axon.

[27]Growth [ edit]Axon of 9 day old mouse with growth cone visible Growing axons move through their environment via the growth cone, which is at the tip of the axon. The growth cone has a broad sheet-like extension called a lamellipodium which contain protrusions called filopodia.

The filopodia are the mechanism by which the entire process adheres to surfaces and explores the surrounding environment. Actin plays a major role in the mobility of this system. Environments with high levels of cell adhesion molecules (CAMs) create an ideal environment for axonal growth.

This seems to provide a ""sticky"" surface for axons to grow along. Examples of CAM's specific to neural systems include N-CAM, TAG-1 an axonal glycoprotein [28], and MAG all of which are part of the immunoglobulin superfamily. Another set of molecules called extracellular matrix - adhesion molecules also provide a sticky substrate for axons to grow along.

Examples of these molecules include laminin, fibronectin, tenascin, and perlecan. Some of these are surface bound to cells and thus act as short range attractants or repellents.

Others are difusible ligands and thus can have long range effects. Cells called guidepost cells assist in the guidance of neuronal axon growth. These cells are typically other, sometimes immature, neurons. It has also been discovered through research that if the axons of a neuron were damaged, as long as the soma (the cell body of a neuron) is not damaged, the axons would regenerate and remake the synaptic connections with neurons with the help of guidepost cells.

This is also referred to as neuroregeneration. [29]Nogo-A is a type of neurite outgrowth inhibitory component that is present in the central nervous system myelin membranes (found in an axon). It has a crucial role in restricting axonal regeneration in adult mammalian central nervous system.

In recent studies, if Nogo- A is blocked and neutralized, it is possible to induce long-distance axonal regeneration which leads to enhancement of functional recovery in rats and mouse spinal cord. This has yet to be done on humans. [30] A recent study has also found that macrophages activated through a specific inflammatory pathway activated by the Dectin-1 receptor are capable of promoting axon recovery, also however causing neurotoxicity in the neuron. [31]Classification [ edit]Further information: Nerve conduction velocity The axons of neurons in the human peripheral nervous system can be classified based on their physical features and signal conduction properties.

Axons were known to have different thicknesses (from 0.1 to 20 µm ) [2] and these differences were thought to relate to the speed that an action potential could travel along the axon – its conductance velocity. Erlanger and Gasser proved this hypothesis, and identified several types of nerve fiber, establishing a relationship between the diameter of an axon and its conductance velocity.

They published their findings in 1941 giving the first classification of axons. Axons are classified in two systems. The first one introduced by Erlanger and Gasser, grouped the fibers into three main groups using the letters A, B, and C. These groups, group A, group B, and group C include both the sensory fibers ( afferents) and the motor fibres ( efferents ).

The first group A, was subdivided into alpha, beta, gamma, and delta fibers - Aα, Aβ, Aγ, and Aδ. The motor neurons of the different motor fibers, were the lower motor neurons – alpha motor neuron, beta motor neuron, and gamma motor neuron having the Aα, Aβ, and Aγ nerve fibers respectively.

Later findings by other researchers, identified two groups of Aa fibers that were motor fibers. These were then introduced into a system that only included sensory fibers (though some of these were mixed nerves and were also motor fibers).

This system refers to the sensory groups as Types and uses Roman numerals,- Type Ia, Type Ib, Type II, Type III, and Type IV.

Motor [ edit]Lower motor neurons have two kind of fibers: Motor fiber types Type Erlanger-Gasser Classification Diameter (µm) Myelin Conduction velocity Associated muscle fibersα Aα 13-20 Yes 80–120 m/s Extrafusal muscle fibersβ Aβγ Aγ 5-8 Yes 4–24 m/s [32] [33] Intrafusal muscle fibers Sensory [ edit]Different sensory receptors innervate different types of nerve fibers.

Proprioceptors are innervated by type Ia, Ib and II sensory fibers, mechanoreceptors by type II and III sensory fibers and nociceptors and thermoreceptors by type III and IV sensory fibers.

Sensory fiber types Type Erlanger-Gasser Classification Diameter (µm) Myelin Conduction velocity Associated sensory receptors Proprioceptors Mechanoceptors Nociceptors and thermoreceptors Ia Aα 13-20 Yes 80–120 m/s Primary receptors of muscle spindle✔Ib Aα 13-20 Yes 80–120 m/s Golgi tendon organ IIAβ 6-12 Yes 33–75 m/s Secondary receptors of muscle spindle All cutaneous mechanoreceptors✔IIIAδ1-5 Thin 3–30 m/s Free nerve endings of touch and pressure Nociceptors of lateral spinothalamic tract Cold thermoreceptors✔IVC0.2-1.5 No 0.5-2.0 m/s Nociceptors of anterior spinothalamic tract Warmth receptors Autonomic [ edit]The autonomic nervous system has two kinds of peripheral fibers: Fiber types Type Erlanger-Gasser Classification Diameter (µm) Myelin [34]Conduction velocitypreganglionic fibers B 1–5 Yes 3–15 m/spostganglionic fibers C 0.2–1.5 No 0.5–2.0 m/s Clinical significance [ edit]Main articles: Nerve injury, Peripheral neuropathy, and Demyelinating disease In order of degree of severity, injury to a nerve can be described as neurapraxia, axonotmesis, or neurotmesis.

Concussion is considered a mild form of diffuse axonal injury. [35] The dysfunction of axons in the nervous system is one of the major causes of many inherited neurological disorders that affect both peripheral and central neurons.

[4]Demyelination of axons causes the multitude of neurological symptoms found in the disease multiple sclerosis. Dysmyelination is the abnormal formation of the myelin sheath. This is implicated in several leukodystrophies, and also in schizophrenia. [36] [37] [38]History [ edit]German anatomist Otto Friedrich Karl Deiters is generally credited with the discovery of the axon by distinguishing it from the dendrites. [4] Swiss Rüdolf Albert von Kölliker and German Robert Remak were the first to identify and characterize the axon initial segment.

Kölliker named the axon in 1896. [39] Alan Hodgkin and Andrew Huxley also employed the squid giant axon (1939) and by 1952 they had obtained a full quantitative description of the ionic basis of the action potential, leading to the formulation of the Hodgkin–Huxley model. Hodgkin and Huxley were awarded jointly the Nobel Prize for this work in 1963. The formulas detailing axonal conductance were extended to vertebrates in the Frankenhaeuser–Huxley equations.

Louis-Antoine Ranvier was the first to describe the gaps or nodes found on axons and for this contribution these axonal features are now commonly referred to as the nodes of Ranvier.

Santiago Ramón y Cajal, a Spanish anatomist, proposed that axons were the output components of neurons, describing their functionality. [4] Erlanger and Gasser earlier developed the classification system for peripheral nerve fibers, [40] based on axonal conduction velocity, myelination, fiber size etc. The understanding of the biochemical basis for action potential propagation has advanced further, and includes many details about individual ion channels.

Other animals [ edit]The axons in invertebrates have been extensively studied. The longfin inshore squid, often used as a model organism has the longest known axon. [41] The giant squid has the largest axon known. Its size ranges from a half (typically) to one millimetre in diameter and is used in the control of its jet propulsion system.

The fastest recorded conduction speed is found in the ensheathed axons of the Kuruma shrimp, [42] ranging between 90 and 200 m/s [43] ( cf 100-120 m/s for the fastest myelinated vertebrate axon. )See also [ edit]Axon guidance Electrophysiology Nerve guidance conduit Neuronal tracing Pioneer axon References [ edit]^ Yau, KW (1976). ""Receptive fields, geometry and conduction block of sensory neurons in the CNS of the leech"". J. Physiol.

Lond. 263 (3): 513–538. doi: 10.1113/jphysiol.1976.sp011643. PMC 1307715. PMID 1018277.^ a b c d e Squire, Larry (2013). Fundamental neuroscience (4th ed. ed.). Amsterdam: Elsevier/Academic Press. pp. 61–65. ISBN 978-0-12-385-870-2.^ a b c Luders, E.; Thompson, P. M.; Toga, A. W. (18 August 2010). ""The Development of the Corpus Callosum in the Healthy Human Brain"". Journal of Neuroscience. 30 (33): 10985–10990.

doi: 10.1523/JNEUROSCI.5122-09.2010. PMC 3197828.^ a b c d e f Debanne, Dominique; Campanac, Emilie; Bialowas, Andrzej; Carlier, Edmond; Alcaraz, Gisèle (Apr 2011). ""Axon physiology"". Physiological Reviews. 91 (2): 555–602. doi: 10.1152/physrev.00048.2009. PMID 21527732.^ Clark, BD; Goldberg, EM; Rudy, B (Dec 2009). ""Electrogenic tuning of the axon initial segment"". The Neuroscientist : a review journal bringing neurobiology, neurology and psychiatry. 15 (6): 651–68. doi: 10.1177/1073858409341973. PMC 2951114. PMID 20007821.^ Wollner, DA; Catterall, WA (Nov 1986).

""Localization of sodium channels in axon hillocks and initial segments of retinal ganglion cells"". Proceedings of the National Academy of Sciences of the United States of America. 83 (21): 8424–8.

doi: 10.1073/pnas.83.21.8424. PMC 386941. PMID 2430289.^ a b c d e Alberts, Bruce (2004). Essential cell biology : an introduction to the molecular biology of the cell (2nd. ed.). New York [u.a. ]: Garland. pp. 584–587. ISBN 0-8153-3481-8.^ a b Alberts, Bruce (2002).

Molecular biology of the cell (4th. ed.). New York [u.a. ]: Garland. pp. 979–981. ISBN 0-8153-4072-9.^ Sadler, T. (2010). Langman's medical embryology (11th ed.). Philadelphia: Lippincott William & Wilkins. p. 300. ISBN 978-0-7817-9069-7.^ Hess, A; Young, JZ (November 20, 1952). ""The nodes of Ranvier"". Proceedings of the Royal Society. Series B. 140 (900): 301–320. doi: 10.1098/rspb.1952.0063. JSTOR 82721. PMID 13003931.^ Robbins, A; Fox, S (Nov 2013). ""Short Duration Waveforms Recorded Extracellularly from Freely Moving Rats are Representative of Axonal Activity"".

Frontiers in Neural Circuits. 7 (181): 7–11. doi: 10.3389/fncir.2013.00181. PMC 3831546. PMID 24348338.^ Rongjing Ge, Hao Qian and Jin-Hui Wang* (2011) Molecular Brain 4 (19), 1~11^ Rongjing Ge, Hao Qian, Na Chen and Jin-Hui Wang* (2014) Molecular Brain 7 (26):1-16^ Chen, Na; Yu, Jiandong; Qian, Hao; Jin-Hui (2010). ""Axons Amplify Somatic Incomplete Spikes into Uniform Amplitudes in Mouse Cortical Pyramidal Neurons"". PLOS ONE. 5 (7): e11868. doi: 10.1371/journal.pone.0011868. PMC 2912328. PMID 20686619.^ Wolpert, Lewis (2015).

Principles of development (5th ed.). pp. 520–524. ISBN 978-0-19-967814-3.^ Fletcher, TL; Banker, GA (Dec 1989). ""The establishment of polarity by hippocampal neurons: the relationship between the stage of a cell's development in situ and its subsequent development in culture"". Developmental Biology. 136 (2): 446–54. doi: 10.1016/0012-1606 (89)90269-8. PMID 2583372.^ Jiang, H; Rao, Y (May 2005).

""Axon formation: fate versus growth"". Nature Neuroscience. 8 (5): 544–6. doi: 10.1038/nn0505-544. PMID 15856056.^ Goslin, K; Banker, G (Apr 1989). ""Experimental observations on the development of polarity by hippocampal neurons in culture"". The Journal of Cell Biology. 108 (4): 1507–16. doi: 10.1083/jcb.108.4.1507. PMC 2115496. PMID 2925793.^ Lamoureux, P; Ruthel, G; Buxbaum, RE; Heidemann, SR (Nov 11, 2002). ""Mechanical tension can specify axonal fate in hippocampal neurons"". The Journal of Cell Biology.

159 (3): 499–508. doi: 10.1083/jcb.200207174. PMC 2173080. PMID 12417580.^ a b Arimura, N; Kaibuchi, K (Mar 2007). ""Neuronal polarity: from extracellular signals to intracellular mechanisms"". Nature Reviews. Neuroscience. 8 (3): 194–205. doi: 10.1038/nrn2056. PMID 17311006.^ Neuroglia and pioneer neurons express UNC-6 to provide global and local netrin cues for guiding migrations in C. elegans^ Serafini, T; Kennedy, TE; Galko, MJ; Mirzayan, C; Jessell, TM; Tessier-Lavigne, M (Aug 12, 1994).

""The netrins define a family of axon outgrowth-promoting proteins homologous to C. elegans UNC-6"". Cell. 78 (3): 409–24. doi: 10.1016/0092-8674 (94)90420-0. PMID 8062384.^ Hong, K; Hinck, L; Nishiyama, M; Poo, MM; Tessier-Lavigne, M; Stein, E (Jun 25, 1999). ""A ligand-gated association between cytoplasmic domains of UNC5 and DCC family receptors converts netrin-induced growth cone attraction to repulsion"". Cell. 97 (7): 927–41. doi: 10.1016/S0092-8674 (00)80804-1. PMID 10399920.^ Hedgecock, EM; Culotti, JG; Hall, DH (Jan 1990).

""The unc-5, unc-6, and unc-40 genes guide circumferential migrations of pioneer axons and mesodermal cells on the epidermis in C. elegans"". Neuron. 4 (1): 61–85. doi: 10.1016/0896-6273 (90)90444-K. PMID 2310575.^ Huang, EJ; Reichardt, LF (2003).

""Trk receptors: roles in neuronal signal transduction"". Annual Review of Biochemistry. 72: 609–42. doi: 10.1146/annurev.biochem.72.121801.161629. PMID 12676795.^ a b Da Silva, JS; Hasegawa, T; Miyagi, T; Dotti, CG; Abad-Rodriguez, J (May 2005). ""Asymmetric membrane ganglioside sialidase activity specifies axonal fate"". Nature Neuroscience.

8 (5): 606–15. doi: 10.1038/nn1442. PMID 15834419.^ Bradke, F; Dotti, CG (Mar 19, 1999). ""The role of local actin instability in axon formation"". Science. 283 (5409): 1931–4. doi: 10.1126/science.283.5409.1931. PMID 10082468.^ Furley, AJ; Morton, SB; Manalo, D; Karagogeos, D; Dodd, J; Jessell, TM (6 April 1990). ""The axonal glycoprotein TAG-1 is an immunoglobulin superfamily member with neurite outgrowth-promoting activity"".

Cell. 61 (1): 157–70. doi: 10.1016/0092-8674 (90)90223-2. PMID 2317872.^ Kunik, D (2011). ""Laser-based single-axon transection for high-content axon injury and regeneration studies"". PLo S ONE. 6 (11): e26832. doi: 10.1371/journal.pone.0026832. PMC 3206876. PMID 22073205.^ Schwab, Martin E. (2004). ""Nogo and axon regeneration"". Current Opinion in Neurobiology. 14 (1): 118–124. doi: 10.1016/j.conb.2004.01.004.

PMID 15018947.^ Gensel; et al. (2009). ""Macrophages promote axon regeneration with concurrent neurotoxicity"". Journal of Neuroscience. 29 (12): 3956–3968. doi: 10.1523/JNEUROSCI.3992-08.2009. PMC 2693768. PMID 19321792.^ Andrew, B. L.; Part, N. J. (1972). ""Properties of fast and slow motor units in hind limb and tail muscles of the rat"". Q J Exp Physiol Cogn Med Sci. 57 (2): 213–225. PMID 4482075.^ Russell, N. J. (1980). ""Axonal conduction velocity changes following muscle tenotomy or deafferentation during development in the rat"". J Physiol. 298: 347–360. PMC 1279120. PMID 7359413.^ Pocock, Gillian; et al. (2004). Human Physiology (Second ed.).

New York: Oxford University Press. pp. 187–189. ISBN 0-19-858527-6.^ e Medicine - Traumatic Brain Injury: Definition, Epidemiology, Pathophysiology : Article by Segun T Dawodu, MD, FAAPMR, FAANEM, CIME, Dip MI (RCSed)^ Krämer-Albers EM, Gehrig-Burger K, Thiele C, Trotter J, Nave KA (November 2006).

""Perturbed interactions of mutant proteolipid protein/DM20 with cholesterol and lipid rafts in oligodendroglia: implications for dysmyelination in spastic paraplegia"". J. Neurosci. 26 (45): 11743–52. doi: 10.1523/JNEUROSCI.3581-06.2006. PMID 17093095.^ Matalon R, Michals-Matalon K, Surendran S, Tyring SK (2006). ""Canavan disease: studies on the knockout mouse"". Adv. Exp. Med. Biol. Advances in Experimental Medicine and Biology. 576: 77–93; discussion 361–3. doi: 10.1007/0-387-30172-0_6. ISBN 978-0-387-30171-6. PMID 16802706.^ Tkachev D, Mimmack ML, Huffaker SJ, Ryan M, Bahn S (August 2007).

""Further evidence for altered myelin biosynthesis and glutamatergic dysfunction in schizophrenia"". Int. J. Neuropsychopharmacol. 10 (4): 557–63. doi: 10.1017/S1461145706007334. PMID 17291371.^ Finger, Stanley (1994). Origins of neuroscience : a history of explorations into brain function. Oxford University Press.

p. 47. ISBN 9780195146943. OCLC 27151391. Kölliker would give the ""axon"" its name in 1896.^ Sansom B, ""Reflex Isolation"" http://www.sansomnia.com^ Hellier, Jennifer L. (16 December 2014). ""The Brain, the Nervous System, and Their Diseases [3 volumes]"". ABC-CLIO.^ Cite error: The named reference Daniel was invoked but never defined (see the help page ).^ J. L. Salzer; B. Zalc (24 October 2016). ""Myelination"". Current Biology. 26 (20): R971–R975. doi: 10.1016/j.cub.2016.07.074. External links [ edit]Histology image: 3_09 at the University of Oklahoma Health Sciences Center - ""Slide 3 Spinal cord ""- Bialowas, Andrzej, Carlier, Edmond, Campanac, Emilie, Debanne, Dominique, Alcaraz. Axon Physiology, Gisèle PHYSIOLOGICAL REVIEWS, V. 91 (2), 04/2011, p. 555-602. [ hide]v t e Nervous tissue CNSTissue Types Grey matter White matter Projection fibers Association fiber Commissural fiber Lemniscus Funiculus Fasciculus Nerve tract Decussation Commissure Neuropil Meninges Cell Types Neuronal Pyramidal Purkinje Granule Glialinsulating: Myelination: Oligodendrocyteother Astrocyte Radial glial cell Ependymal cells Tanycyte Microglia PNSGeneral Dorsal Root Ganglion Ramus Ventral Root Ramus Ramus communicans Gray White Autonomic ganglion ( Preganglionic nerve fibers Postganglionic nerve fibers)Connective tissues Epineurium Perineurium Endoneurium Nerve fascicle Neuroglia Myelination: Schwann cell Neurilemma Myelin incisure Node of Ranvier Internodal segment Satellite glial cell Neurons / nerve fibers Parts Soma Axon hillock Axon Telodendron Axon terminals Axoplasm Axolemma Neurofibril/neurofilament Dendrite Nissl body Dendritic spine Apical dendrite / Basal dendrite Types Bipolar Unipolar Pseudounipolar Multipolar Interneuron Renshaw Afferent nerve fiber / Sensory neuron GSA GVA SSA SVA fibers Ia or Aα Ib or Golgi or Aα II or Aβ and Aγ III or Aδ or fast pain IV or C or slow pain Efferent nerve fiber / Motor neuron GSE GVE SVE Upper motor neuron Lower motor neuronα motorneuron β motorneuronγ motorneuron Termination Synapse Electrical synapse / Gap junction Chemical synapse Synaptic vesicle Active zone Postsynaptic density Autapse Ribbon synapse Neuromuscular junction Sensory receptors Meissner's corpuscle Merkel nerve ending Pacinian corpuscle Ruffini ending Muscle spindle Free nerve ending Nociceptor Olfactory receptor neuron Photoreceptor cell Hair cell Taste bud Authority control GND: 4200576-0Categories: Neurohistology "

synapsethe junction between the processes of two neurons or between a neuron and an effectororgan, where neural impulses are transmitted by chemical means. The impulse causes therelease of a neurotransmitter (e.g. acetylcholine or norepinephrine) from the presynapticmembrane of the axon terminal.

synapse

"synapse Also found in: Dictionary, Thesaurus, Acronyms, Encyclopedia, Wikipedia .synapse [ sin´aps] the junction between the processes of two neurons or between a neuron and an effector organ,where neural impulses are transmitted by chemical means. The impulse causes the release of a neurotransmitter (e.g., acetylcholine or norepinephrine) from the presynaptic membrane of the axonterminal.

The neurotransmitter molecules diffuse across the synaptic cleft, bind with specificreceptors on the postsynaptic membrane, causing depolarization or hyperpolarization of thepostsynaptic cell. See also neuron. Components of a synapse. From Applegate, 2000.axoaxonic synapse one between the axon of one neuron and the axon of another neuron.axodendritic synapse one between the axon of one neuron and the dendrites of another.axodendrosomatic synapse one between the axon of one neuron and the dendrites and body of another.axosomatic synapse one between the axon of one neuron and the body of another.dendrodendritic synapse one from a dendrite of one cell to a dendrite of another.electrotonic synapse a special type of gap junction found in tissue such as the myocardium.

Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.syn·apse, pl.syn·aps·es ( sin'aps, sĭ-naps'; sy-nap'sez ), Avoid mispronouncingthe plural of this English word sin-ap'sēz. The functional membrane-to-membrane contact of the nerve cell with another nerve cell, an effector (muscle or gland) cell, or a sensory receptor cell.

The synapse subserves thetransmission of nerve impulses, commonly from a variably large (1-12 mcm), generally knob-shaped or club-shaped axon terminal (the presynaptic element) to the circumscript patch of the receiving cell's plasma membrane (the postsynaptic element) on which the synapseoccurs.

In most cases, the impulse is transmitted by means of a chemical transmittersubstance (such as acetylcholine, γ-aminobutyric acid, dopamine, or norepinephrine)released into a synaptic cleft (15-50 nm wide) that separates the presynaptic from thepostsynaptic membrane; the transmitter is stored in quantal form in round or ellipsoid,membrane-bound synaptic vesicles (10-50 nm in diameter) in the presynaptic element.

In other synapses, transmission takes place by direct propagation of the bioelectrical potentialfrom the presynaptic to the postsynaptic membrane; in such electrotonic synapses (""gapjunctions""), the synaptic cleft is no more than about 2 nm wide.

In most cases, synaptictransmission takes place in only one direction (""dynamic polarity"" of the synapse), but in some synapses synaptic vesicles occur on both sides of the synaptic cleft, which suggestthe possibility of reciprocal chemical transmission.

[syn- + G. hapto, to clasp]Farlex Partner Medical Dictionary © Farlex 2012synapse/syn·apse/ ( sin´aps) the site of functional apposition between neurons, where an impulse is transmitted from one to another, usually by a chemical neurotransmitter released by theaxon terminal of the presynaptic neuron.

The neurotransmitter diffuses across the gap to bind withreceptors on the postsynaptic cell membrane and cause electrical changes in that neuron (depolarization/excitation or hyperpolarization/inhibition). Diagram of three synapses. Nerve impulse is indicated by arrows, showing that the direction of passage is from the terminal arborization (TA) or nerve endings of the axon of one neuron to the dendrites (D) of another neuron.

Dorland's Medical Dictionary for Health Consumers. © 2007 by Saunders, an imprint of Elsevier, Inc. All rights reserved.synapse (sĭn′ăps′, sĭ-năps′)n. The junction across which a nerve impulse passes from an axon terminal to a neuron, musclecell, or gland cell.intr.v.

syn·apsed, syn·apsing, syn·apses1. To form a synapse.2. To undergo synapsis. The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company.

Published by Houghton Mifflin Company. All rights reserved.synapse [sin′aps, sinaps′]Etymology: Gk, synaptein, to join1 n, the region surrounding the point of contact between two neurons or between a neuron and an effector organ, across which nerve impulses are transmitted through the action of a neurotransmitter, such as acetylcholine or norepinephrine. When an impulse reaches theterminal point of one neuron, it causes the release of the neurotransmitter.

The neurotransmitterdiffuses across the gap between the two cells to bind with receptors in the other neuron, muscle, or gland, triggering electric changes that either inhibit or continue the transmission of theimpulse. Synapses are polarized so that nerve impulses normally travel in only one direction;they are also subject to fatigue, oxygen deficiency, anesthetics, and other chemical agents.

Kinds of synapses include axoaxonic synapse, axodendritic synapse, axodendrosomatic synapse, axosomatic synapse, and dendrodendritic synapse. Compare ephapse.2 v, to form a synapse or connection between neurons.3 v, (in genetics) to form a synaptic fusion between homologous chromosomes during meiosis.synaptic, adj.

Mosby's Medical Dictionary, 9th edition. © 2009, Elsevier.syn·apse ( sin'aps) The functional membrane-to-membrane contact of the nerve cell with another nerve cell, an effector (muscle, gland) cell, or a sensory receptor cell. The synapse subserves thetransmission of nerve impulses, commonly from a club-shaped axon terminal (the presynapticelement) to the circumscript patch of the plasma membrane of the receiving cell (thepostsynaptic element) on which the synapse occurs.

In most cases, the impulse is transmitted by means of a chemical transmitter substance (such as acetylcholine, gamma-aminobutyric acid, dopamine, norepinephrine) released into a synaptic cleft that separatesthe presynaptic from the postsynaptic membrane; the transmitter is stored in synapticvesicles in the presynaptic element. In other synapses, transmission takes place by directpropagation of the bioelectrical potential from the presynaptic to the postsynaptic membrane.

Synonym (s): synapsis. [ syn- + G. hapto, to clasp]Medical Dictionary for the Health Professions and Nursing © Farlex 2012synapse (sin'aps) [Gr.

synapsis, point of contact]SYNAPSE: Axon terminal synapse The space between the junction of two neurons in a neural pathway, where the termination of theaxon of one neuron comes into close proximitywith the cell body or dendrites of another. Theelectrical impulse traveling along a presynapticneuron to the end of its axon releases a chemical neurotransmitter that stimulates or inhibits an electrical impulse in the postsynapticneuron; synaptic transmission is in one directiononly.

Synapses are susceptible to fatigue, offer a resistance to the passage of impulses, andare markedly susceptible to the effects of oxygen deficiency, anesthetics, and otheragents, including therapeutic drugs and toxicchemicals. Synonym: synapsis (1) See:illustrationaxodendritic synapse The synapse between an axon of one neuron and the dendrites of another.axodendrosomatic synapse The synapse between the axon of one neuron and the dendrites and cell body of another.axosomatic synapse The synapse between the axon of one neuron and the cell body of another.

Medical Dictionary, © 2009 Farlex and Partnerssynapse The junctional area between two connected nerves, or between a nerve and theeffector organ (a muscle fibre or a gland). Nerve impulses are transmitted across a synapse by means of a chemical NEUROTRANSMITTER such as ACETYLCHOLINE or NORADRENALINE. Synapses allow impulses to pass in one direction only and single brain cells may have more than 15 000 synapses with other cells.

This complexity, allowing logical ‘gate’ operation, partly or whollyunderlies the computational and storage abilities of the brain. Collins Dictionary of Medicine © Robert M. Youngson 2004, 2005synapsethe point at which one nerve cell connects with another and at which transmission of an impulse takes place by chemical means.

When an impulse arrives at a synapse it causes a synaptic vesicle to move towards the presynaptic membrane. On contacting the membrane it discharges the contained transmitter substance into the synaptic cleft, across which it diffuses to the postsynaptic membrane which it depolarizes. This causes a positive charge to develop (excitory postsynaptic potential -EPSP) because of sodium ions flowing into the postsynaptic nerve cell.

When the positive charge builds up sufficiently it generates an actionpotential which is usually unidirectional. See ENDPLATE, MOTOR and Fig. 148.the point of contact of homologous regions of DNA prior to RECOMBINATION, as in thepairing of homologous chromosomes during MEIOSIS.

Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005Synapse A connection between nerve cells, by which nervous excitation is transferred from one cell to theother. Mentioned in: Alpha 1 -Adrenergic Blockers, Cocaine Gale Encyclopedia of Medicine. Copyright 2008 The Gale Group, Inc. All rights reserved.synapsethe name given by Charles Sherrington in 1897 to the site of transmission of information from one neuron to another or (in current usage) to individual cells of a muscle or gland.

The majority are chemical synapses involving release of a neurotransmitter from the presynapticnerve ending which binds to receptors on the postsynaptic cell, opening ion channels and leading to local depolarization.

At the very many fewer electrical synapses (gap junctions) the abutting cellsare in tight contact and there is faster, direct electrical coupling, e.g. between neurons within thebrain. See also action potential, neuromuscular junction. Dictionary of Sport and Exercise Science and Medicine by Churchill Livingstone © 2008 Elsevier Limited.

All rights reserved.synapsemembrane-membrane contact of nerve cell/fibre with another nerve cell/fibre,effector organ (e.g. muscle or gland) or sensory receptor cell, across which the nerve impulse is transmitted from presynaptic element (i.e.

axon terminal) to postsynaptic element (i.e. receivingnerve cell axon/dendrite/plasma membrane); see synaptic cleft Illustrated Dictionary of Podiatry and Foot Science by Jean Mooney © 2009 Elsevier Limited. All rights reserved.synapse (siˑ·naps),n the junction between two neurons across which nerve impulses are conducted.

Jonas: Mosby's Dictionary of Complementary and Alternative Medicine. (c) 2005, Elsevier.synapse The place where a nerve impulse is transmitted from one neuron to another. This transmission is usually mediated by neurotransmitters (e.g. acetylcholine, noradrenaline (norepinephrine),glutamate, etc.)

that are released by the presynaptic neuron, then diffuse across thesynaptic cleft (about 20-50 nm wide) to bind to receptor sites on the postsynaptic membraneand generate an electrical change in the postsynaptic neuron, which results in eitherdepolarization (excitation) or hyperpolarization (inhibition). This is often referred to as a chemical synapse. There is another type of synapse called an electrotonic synapse (electrical synapse) in which electrical impulses are transmitted via ionic currents from oneneuron to another by direct propagation across a gap junction (2-3nm wide).

Electrotonicsynapses are rare in vertebrates and have been found at only a few central nervous sites. It is estimated that a cortical neuron, for example, makes some 5000-10 000 synapses withsurrounding neurons. See neuron; neurotransmitter; receptor potential. Millodot: Dictionary of Optometry and Visual Science, 7th edition. © 2009 Butterworth-Heinemannsyn·apse, pl. synapses ( sin'aps, -ĕz) Functional membrane-to-membrane contact of nerve cell with another. [ syn- + G. hapto, to clasp]Medical Dictionary for the Dental Professions © Farlex 2012synapse (sin´aps),n the region of contact between the processes of two adjacent neurons forming the placewhere a nervous impulse is transmitted from the axon of one neuron to the dendrites of another. It also is called thesynaptic junction. Mosby's Dental Dictionary, 2nd edition. © 2008 Elsevier, Inc. All rights reserved.

synapsethe junction between the processes of two neurons or between a neuron and an effectororgan, where neural impulses are transmitted by chemical means. The impulse causes therelease of a neurotransmitter (e.g. acetylcholine or norepinephrine) from the presynapticmembrane of the axon terminal.

The neurotransmitter molecules diffuse across the synapticcleft, bind with specific receptors on the postsynaptic membrane, causing depolarization or hyperpolarization of the postsynaptic cell.

See also neuron.adrenergic synapsethe neurotransmitter is norepinephrine. See also adrenergic (1).axoaxonic synapsesee axoaxonic.axodendritic synapsesee axodentritic.axodendrosomatic synapseone between the axon of one neuron and the dendrites and body of another.axosomatic synapsesee axosomatic.cholinergic synapsethe neurotransmitter is acetylcholine.

See also cholinergic.dendrodendritic synapseone from a dendrite of one cell to a dendrite of another.excitatory synapsea synapse in which the transmission of impulses is electrical not chemical. Found only in fish and invertebrates.inhibitory synapsehyperpolarizing electrical current is used to raise the threshold for the stimulation of a discharge of an impulse from the particular kind of nerve cell, found only in fish.

Saunders Comprehensive Veterinary Dictionary, 3 ed. © 2007 Elsevier, Inc. All rights reserved Want to thank TFD for its existence? Tell a friend about us, add a link to this page, or visit the webmaster's page for free fun content . Link to this page: Facebook Twitter "

A neuron contains four main parts: the cell body, dendrites, the axon and the axon terminal. The axon is a long projection from the cell body of the neuron that transmits signals from one nerve cell to another. Bundles of axons are known as nerves. The longest axon in the human body is the sciatic nerve.

What Is the Function of the Axon Terminal?

Science Human Anatomy Nerves Q: What Is the Function of the Axon Terminal? A: Quick Answer The function of the axon terminal is to transmit a neurotransmitter from one neuron to another. The neurotransmitter is released from the end of the axon of one neuron and binds to the dendrites of the target neuron.

Neurotransmitters may be classified as excitatory or inhibitory or both, as in the case of dopamine or acetylcholine. Continue Reading Keep Learning How Do I Describe the Structure of a Neuron? What Are Telodendria? What Is the Function of Nodes of Ranvier? Full Answer

It spans from the base of the spine to the big toe of each foot. Axons in vertebrates are covered in a myelin sheath.

The sheath is made of two different types of cells, depending on what branch of the nervous system the axon is located on. Oligodendrocytes make up the myelin sheath on axons in the central nervous system. Schwann cells form the sheath in peripheral system neurons. Both oligodendrocytes and Schwann cells are types of glial cells. The myelin sheath increases the speed at which signals are sent from neuron to neuron.

Learn more about Nerves Sources: macalester.edu sciencedaily.com psychology.about.com britannica.com Related Questions Q: What Is the Function of the Thalamus?

A: The function of the thalamus is to regulate the body's voluntary motor control, consciousness and its sleep/wake cycle. It also regulates the senses of sig... Full Answer >Filed Under: Nerves Q: What Is the Function of the Lentiform Nucleus?

A: The function of the lentiform nucleus involved in maintaining the muscular tone of the body and assisting in controlling movement, mainly of the limbs of t... Full Answer >Filed Under: Nerves Q: What Is the Function of the Myelin Sheath? A: The function of the myelin sheath is to facilitate the conduction of electrical impulses through the nerve cells.

The myelin sheath is made out of a modifi... Full Answer >Filed Under: Nerves Q: What Is the Cognitive Function of the Brain?

A: Cognition is the primary function of the brain. The brain is responsible for such cognitive processes as perception, thought, interpretation, emotion, atte... Full Answer >Filed Under: Nerves You May Also Like Q: What Is the Function of the Musculoskeletal System? Q: What Is the Function of the Lentiform Nucleus? Q: What Is the Function of a High Power Objective? Q: What Is the Function of Red Marrow? Q: What Is the Function of Renal Medulla? Q: Is Voluntary Control of Skeletal Muscles Provided by the Nervous System?

13refers to the end of an axon or an axon branch, which forms a synapse on a neuron or other target. See also terminal button. AXON TERMINAL: ""The axon terminal of a neuron is most commonly located at the end of the axon, nearest to the synaptic cleft .

AXON TERMINAL

"AXON TERMINALBy Nugent, Pam M. S. - April 7, 20

""Related Psychology Terms TERMINAL BUTTONAXO-AXONAL SYNAPSESYNAPSEAXON HILLOCKSYNAPTIC VESICLESYNAPTIC CLEFTRELEASE ZONEDALE'S LAWNERVE FIBERPOSTSYNAPTICCite this page: Nugent, Pam M. S., ""AXON TERMINAL,"" in Psychology Dictionary.org, April 7, 2013, https://psychologydictionary.org/axon-terminal/ (accessed March 31, 2018).tweet "

. Each nerve cell has one and only one axon. Typical axons have relatively few branches, except near the terminal end. The diameter of an axon is uniform along its entire length. The terminal branches of an axon make synaptic contacts onto other nerve cells (or with peripheral effectors, i.e. muscles and glands).

Neurons and Support Cells

"HISTO HOME SSB Index Nervous Tissue Muscle Tissue Skeletal Tissue RESOURCE CENTERNeurons and Support Cells Please note that this guide is intended to complement, NOT to replace, textbook readings (i.e., Kandel et al.). Text References to Principles of Neural Science, by Kandel, Schwartz and Jessell. [ About Eric Kandel]Introductory comments / How to read this page.

NERVE CELLSBasic structure and function Myelin Recognizing nerve cells SUPPORT TISSUESchwann cells Glial cells Oligodendroglia Astrogliamicrovasculature Blood-brain barrier Microglia CNS blood vessels Ependyma / choroid plexus / cerebrospinal fluid Meninges SOME EXAMPLES of nervous tissue Spinal smear Spinal cord section Cerebral cortex Cerebellar cortex Peripheral ganglia Retina PERIPHERAL NERVESComposition and appearance of peripheral nerves Sensory and motor nerve endings CENTRAL NERVOUS SYSTEMGray Matter, White Matter, Cortex, Nuclei and Fiber Tracts Sensory Neurons, Motor Neurons, and Interneurons Synaptic Relays Afferent and Efferent Axons Ascending and Descending Pathways Long-Axon And Short-Axon Neurons Neuron Names Nervous tissue pathology SAQ Self Assessment practice Questions Online slides of the nervous system -- normal | pathology These specimens at the Virtual Slidebox (University of Iowa Department of Pathology) may be examined with full range of magnification and movement.

Requires Java and fast internet connection . Link to LUMEN (Loyola University Medical Education Network), click on ""Part 6: Neural Tissue"". Link to Blue Histology . Click on ""Notes"", then ""Nervous Tissue"". University of Arizona Health Science Center, Blood Brain Barrier.

More neuroscience links Cells-R-Us (illustrated text of a public lecture on the brain)Image index Histology textbooks are NOT recommended for the study of nervous tissue. Most histology textbooks begin with relatively insignificant, and often misleading, details rather than emphasizing features important for understanding nervous tissue function. Recommended are selected chapters in in Kandel, Schwartz and Jessell, Principles of Neural Science.

Kandel's classic text is remarkable. The extended table of contents can be read, just as if it were a ""capsule"" textbook. In about two dozen pages following immediately after the chapter listing, all of the subheadings from every chapter are presented, each as a complete sentence.

This extended table of contents offers a concise summary of major ideas. Your study through this entire unit can be usefully guided by this summary.

You should, at a minimum, be fluent in the vocabulary of this summary so that every sentence here is meaningful to you. Senior author Eric Kandel received the 2000 Nobel Prize for Physiology and Medicine for work on ""signal transduction in the nervous system"" ( Kandel's Nobel Prize lecture ). Choose: 5th edition, 2013, 4th edition, 2000, or 3rd. edition, 1991.5th edition, TBAHistorical overview.

Chapter 1 provides an excellent narrative of how science and medicine have understood the brain. This chapter is available online at Amazon.com. Basic cellular organization of the nervous system is described in Chapter 2. This chapter is available online at Amazon.com. Nerve cell structure is described in detail in Chapter 4 and subsequent chapters. Begin by reading the extended table of contents.

[ Appendix A reviews basic physics of electrical circuits, for those who wish to go there. ]CSF, meninges, choroid plexus and blood brain barrier are described in Appendix D4th edition, 2000Historical overview.

Chapter 1 provides an excellent narrative of how science and medicine have understood the brain. Basic cellular organization of the nervous system is described in Chapter 2. Nerve cell structure is described in detail in Chapter 4. Begin by reading the extended table of contents ( p. x ). Add more only as the need arises. Subcellular basis for neural function. Begin with the extended table of contents ( pp.

x-xi ). Check out Chapters 3 ( genes ), Chapter 5 ( proteins ), and Chapters 6 - 9 ( electrical activity ). Dip into the main text for principal learning issues (e.g., resting potential and action potential).

[ Appendix A reviews basic physics of electrical circuits, for those who wish to go there. ]3rd edition, 1991Historical overview. Chapter 1 provides an excellent narrative of how science and medicine have understood the brain. Basic cellular organization of the nervous system is described in Chapter 2.

Nerve cell structure is described in detail in Chapter 3. Begin by reading the extended table of contents ( p. xiii ). Add more only as the need arises. Subcellular basis for neural function. Begin with the extended table of contents ( pp.

xiv-xv ). Check out Chapters 4 ( proteins ), and Chapters 5 - 8 ( electrical activity ). Dip into the main text for principal learning issues (e.g., resting potential and action potential).

[ Appendix A reviews basic physics of electrical circuits, for those who wish to go there. ]INTRODUCTORY COMMENTSPlease note that this guide is intended to complement, NOT to replace, textbook readings (i.e., Kandel et al.). Nervous tissue has presented extraordinary challenges to science. Historically, a basic appreciation of the cellular composition of nervous tissue did not come until decades after other tissues were fairly well understood.

One reason is that none of the cell types which comprise nervous tissue can be properly visualized in routine histological preparations. Significance: Do not expect examination of nervous system specimens to yield satisfying observations, at least not without an exceptional effort to understand why things look the way they do.

Neuron preparation by Ramón y Cajal Historical note : The most famous pioneer in the descriptive anatomy of nerve cells was Ramón y Cajal . Cajal introduced the four principles which comprise the neuron doctrine (quotes are from Kandel 2006, In Search of Memory, pp.

65-66): Cellularity: ""The nerve cell is the fundamental structural and functional element of the brain. ""Synaptic communication: ""The terminals of one neuron's axon communicate with the dendrites of another neuron only at specialized sites, later named synapses by Sherrington . ""Connection specificity: ""Neurons do not form connections indiscriminately. Rather each nerve cell forms synapses and communicates with certain nerve cells and not with others.

""Dynamic polarization: ""Signals in a neural circuit travel in only one direction. . . Information flows, from the dendrites of a given nerve cell to the cell body [then] along the axon to the presynaptic terminals and then across the synaptic cleft to the dendrites of the next cell, and so on. ""Cajal's 1906 Nobel Prize lecture includes some elegant images of nerve cells in spinal cord and in cerebellar and cerebral cortex.

Click here to see a micrograph of one of Cajal's original nerve cell preparations. Axons, dendrites and synapses -- the most significant features of nerve cells -- cannot be readily seen without specialized techniques such as those used by Cajal.

No other tissue in the body is characterized by cells whose cytoplasmic processes reach out for great distances away from the cell nuclei. This reality puts a special burden on the student as well as the researcher. You cannot simply look at a slide or micrograph, not even an electron micrograph, and truly ""see"" the most interesting features of the nerve cell.

Nerve cell processes are quite thin, often less than a micron (1µm) in diameter. However, the length of axons and dendrites is wondrously great, far greater than ordinary cellular dimensions. Dendrites may extend several millimeters away from the cell body, into a volume the size of a pea. Axon length may exceed a meter (for many sensory and motor axons), and commonly extends for several centimeters. As a simple consequence of this cellular geometry, the cell body of a neuron may comprise less than one percent of the entire cell volume.

From this, you may deduce that the bulk of nervous tissue consists of nerve cell processes rather than nerve cell bodies. The study of neuroanatomy consists largely of understanding the routes travelled by nerve cell axons. Unfortunately, the organization of neural processes, most particularly the full length of axons and dendrites and the synaptic interactions between them, can seldom be visualized directly.

In most other tissues of the body, what you can see in the microscope is directly informative. Consider skin, where a routine section of epidermis reveals almost everything interesting about the size, shape and growth sequence of epidermal cells. Electron microscopy of similar specimens simply adds more finely resolved detail. But making any sense at all of nervous tissue requires that you ""see"" with concepts acquired over decades of research with many special techniques.

When you examine microscope slides or micrographs of nervous tissue, patterns of functional connection cannot usually be seen .

Nevertheless, what you can observe should be interpreted in terms of neuronal functions and connectivity, including unseen axons, dendrites and synapses as well as associated supporting cells. Thus your job for comprehending nervous tissue is not just to look-and-learn, but to think rather deeply, to fit many different views and facts together.

Most of the listed vocabulary terms for neuronal and glial structures are well defined in standard textbooks. You just have to make sense of it all. How to read this page. You might read this page straight down, from top to bottom.

But it is written with hyperlinks to facilitate browsing. You might more profitably check out each link, at least if it suggests a question in your mind, and use your browser's ""back"" arrow to return.

And return repeatedly to the outline at the top of this page to choose the topic that most closely engages your current curiosity. BASIC STRUCTURE OF NERVE CELLS (""NEURONS"")"" Swiftly the brain becomes an enchanted loom, where millions of flashing shuttles weave a dissolving pattern-always a meaningful pattern-though never an abiding one "" ( Sherrington, 1940). Nerve cells comprise the ""enchanted loom"" that is our brain. Here are three absolutely wonderful facts about nerve cells.

The first and most wonderful fact is that, working together, nerve cells can perceive and think and dream. They are us. This is magic of the highest sort. ( See Cells-R-Us for extended discussion. )The second wonderful fact is that nerve cells are much like other cells. Each is essentially a bag of water, surrounded by a fatty membrane and containing an assortment of molecules.

There seems to be nothing about individual nerve cells that cannot be explained, at least in principle, by basic chemistry and biology.

The third wonderful fact is that each nerve cell has a truly magnificent shape. Somehow, this third fact bridges the gap between the mystery that is our mind and the chemistry that is our cells. Somewhere in the shape of nerve cells, in the complexity of connections among billions of such cells, and in the intricate pattern of activity that plays upon those cells, our ""self"" emerges.

*** The following generalities all have exceptions. ***Every nerve cell has three distinctive portions -- a cell body, one axon, and several dendrites. Nerve cells come in extreme variety. In every region of the brain are several different nerve cell types, each distinguished by its own characteristic soma size, dendritic shape, source of synaptic input, destination of axonal output, and chemistry.

Occasional nerve cell types may have characters which depart from the the typical description presented below. Because of this immense variety of nerve cell types, there is no ""one-size-fits-all"" description.

So textbook descriptions of nerve cells tend to present overwhelmingly abundant detail. Although details of nerve cell shape and connectivity are usually insignificant for clinical practice, they can be quite beautiful and are essential for understanding research on brain function. It is also often necessary to learn some ""irrelevant"" detail in order to understand the particular examples used to demonstrate basic functional principles.

Nerve cell bodies look more or less like other body cells, although they do have certain characteristic features . Extending out from each nerve cell body are long cytoplasmic processes, one axon and several dendrites. (These processes usually cannot be distinguished in routine histological preparation. )A typical nerve cell body contains only a small fraction of the total cell volume; the rest is contained in the axon and dendrites.

The spaces between nerve cell bodies with a feltwork of these axonal and dendritic processes, called neuropil (which also includes glial cell processes). The cell body of a nerve cell (also called a soma, plural somata) is basically a cell nucleus surrounded by cytoplasm. Nuclei of nerve cells are large, round and euchromatic with a single prominent nucleolus ( more below ). Cytoplasm of nerve cell bodies is abundantly supplied with masses of rough endoplasmic reticulum (traditionally called Nissl bodies ), numerous Golgi bodies, lots of smooth endoplasmic reticulum, many mitochondria, and extensive cytoskeletal elements (microtubules and various filaments). This metabolic machinery is needed for ongoing maintenance of extensive axonal and dendritic membranes. The axon is a process which is specialized for conducting signals from one nerve cell to another

. Each nerve cell has one and only one axon. Typical axons have relatively few branches, except near the terminal end. The diameter of an axon is uniform along its entire length. The terminal branches of an axon make synaptic contacts onto other nerve cells (or with peripheral effectors, i.e. muscles and glands).

Nerve signals travel along axons away from the cell body and toward synapses at the axonal terminal. Axonal nerve signals, called action potentials are initiated at the axon hillock, the site where an axon arises from the cell body. Action potentials are active, all-or-nothing signals which do not decline in strength as they travel along the axon.. Axons may be myelinated to increase the speed of signal conduction.

Neuron preparation by Ramón y Cajal Dendrites are processes which are specialized for receiving and integrating signals from other nerve cells. A nerve cell typically has several dendrites, each with numerous branches. (The word ""dendrite"" means ""branch"".) The diameter of dendrites typically decreases away from the cell body, so that dendrites taper gradually to fine twigs.

Dendrites typically receive synaptic contacts from axons of many other nerve cells. Synapses often occur on tiny dendritic spines. Nerve signals travel along dendrites toward the cell body. Dendritic nerve signals, called synaptic potentials, arise at synapses. Synaptic potentials are conducted passively (fading with distance). Dendrites are not myelinated. Size and shape of dendritic spines influence synaptic strength. Plasticity of dendritic spine morphology is implicated in memory.

Synapses are points of contact between nerve cells (usually between axon terminals and dendrites), where signals are transmitted from one cell to another. Neurotransmission is usually chemical, based on small molecules called neurotransmitters, secreted by one cell and binding to another.

(Neurotransmission can also be electrical, with ions passing directly from one cell into another. )Each synapse has a pre synaptic side -- an axon terminal -- from which a neurotransmitter is released. Neurotransmitter is usually stored in synaptic vesicles within the presynaptic terminal. Neurotransmitter is released in response to changes in membrane potential associated with arrival of action potentials.

Each synapse has a post synaptic side -- a dendrite or a nerve cell body -- where the membrane is specialized to respond to the binding of neurotransmitter molecules, e.g. by altering membrane ion conductance. Size and shape of dendritic spines influence synaptic strength.

Plasticity of dendritic spine morphology is implicated in memory. Top of page. MYELINMyelin is a fatty covering which envelops many axons and permits action potentials to be propagated at a much greater velocity. Axons with myelin are called myelinated axons. Most myelinated axons are fairly large, ranging from 1µm up to 10µm in diameter (not counting the myelin).

[For perspective, the diameter of a large axon may be greater than that of a capillary. ]Axons without myelin are called, logically enough, un myelinated axons.

Unmyelinated axons are usually quite small, less than 1µm in diameter. Myelin is formed by support cells ( Schwann cells in the peripheral nerve system, oligodendroglia in the CNS) wrapping around the axons. Myelin is not part of, nor produced by, the nerve cell whose axon it envelops. In peripheral nerves, myelin consists of Schwann cell membrane wrapped around and around an axon, while most of the Schwann cell cytoplasm lies alongside the axon.

(See oligodendroglia for myelination of CNS axons. )To visualize myelin formation: Imagine that a Schwann cell is a pillow with the pillowcase representing Schwann cell membrane and the stuffing representing Schwann cell nucleus and cytoplasm.

Next imagine a broomstick (representing the axon) lying across one end of the pillow. Now roll the broomstick up in the pillow, wrapping the pillowcase tightly around and around the broomstick while squeezing the pillow-stuffing into one end.

The tight wrappings of pillowcase now represent the myelin, while the remaining pillow with stuffing represents the Schwann cell body with nucleus and cytoplasm. Myelination of a peripheral axon Animation from Blue Histology, Copyright Lutz Slomianka 1998-2004 (The image should be animated, if you watch patiently.

)A Schwann cell is illustrated with brown cytoplasm. The blue oval is the Schwann cell's nucleus. Observe that as the growing Schwann cell spirals inward around the axon, it wraps its membrane into layers of myelin. The myelin of one Schwann cell wraps about one or two millimeters of an axon. To myelinate the entire length of the axon, many of these Schwann cell wrappings line up end-to-end along the axon.

The points between segments of myelin are called nodes of Ranvier . The stretch of axon between nodes is called an internode. The spacing of nodes is critical for propagation of action potentials. Along myelinated axons, action potentials are regenerated only at the nodes.

Myelin provides insulation (and, more importantly, decreased capacitance) so that the ionic currents at one node can flow efficiently (and quickly) to the next node. This is called saltatory conduction (saltation = jump). In contrast, action potentials propagating along un myelinated axons are regenerated at each point along the way, a much slower process.

[ Hydrodynamic metaphor for saltatory conduction]Clinical notes Because the currents generated at one node are generally sufficient to depolarize axonal membrane two or three nodes away, local anesthesics (which block action potentials but do not prevent current flow) must be distributed across several nodes (several millimeters) in order to produce effective anesthesia.

Because myelinated axons have voltage-dependent sodium channels only at nodes of Ranvier, demyelination (such as that which occurs in multiple sclerosis) effectively prevents the propagation of action potentials. Many details of myelin cannot be well-appreciated by light microscopy. For electron micrographs of myelin in peripheral nerves, see the online Electron Microscopic Atlas of Mammalian Tissues (the text is in German, but most figure labels can be deciphered fairly easily).

Top of page. RECOGNIZING NERVE CELLS in histological preparations. Although axons reach into all parts of the body, the vast majority of nerve cell bodies occur in the central nervous system (brain and spinal cord), in those regions described as gray matter. Relatively few nerve cell bodies occur peripherally, in the ganglia (small clusters of nerve cells) of sympathetic and parasympathetic nervous systems.

Wherever they occur, nerve cell bodies have a distinctive appearance. Nuclei of nerve cells are large, round and euchromatic with a single prominent nucleolus. Because of this distinctive nuclear appearance, neurons are sometimes described as having ""owl-eye"" nuclei or ""fried-egg"" nuclei.

Cytoplasm of all but the smallest nerve cell bodies is substantial and conspicuously basophilic, containing characteristic basophilic masses of rough endoplasmic reticulum that are traditionally called Nissl bodies.

Because these features of nerve cell bodies are related to the heavy metabolic demands imposed by extensive processes, they are exaggerated (i.e., bigger nuclei, more cytoplasm) in those nerve cells which have the longest, largest diameter axons.

Nerve cells with the most extremely long, large diameter axons -- such as pyramidal cells of motor cortex and motor neurons of spinal cord -- are often illustrated as ""typical"" neurons simply because they are big and hence especially easy to visualize. Cerebellar Purkinje cells comprise another ""popular"" type of nerve cell, also large but with a huge dendritic tree rather than an especially long axon.

Neuron preparation by Ramón y Cajal Special stains, like the silver-based Golgi stain, can reveal entire neurons or glial cells (at least as much as fits within the thickness of a single section) by impregnating them with opaque silver.

But this technique yields elegant results only by suppressing any staining of most neighboring cells, so neurons appear in splendid isolation when their essence is one of complex interaction. Similarly, electron microscopy can display elegant synapses, but the narrow view offers few clues about the cells to which the pre- and post-synaptic profiles belong.

Sections of central nervous tissue routinely show neuron cell bodies surrounded by a finely-textured fibrous material often called neuropil (which should not be confused with connective tissue ). This feltwork consists of axons and dendrites (and glial processes), with all the comings and goings that these processes entail. Individual axons and dendrites can be distinguished only in fortuitous sections, and then only for a short length.

The so-called ""molecular"" layers of cerebral and cerebellar cortex consist of neuropil containing relatively few cell bodies (most of the cell bodies lie in deeper layers). Note that a common artefact, resulting from tissue shrinkage, is for a clear "" halo "" to appear around cell bodies and blood vessels.

Although the presence of such halos can be misleading (there is no such space in intact, living nervous tissue), this consistent artefact serves to highlight or emphasize the locations for these structures. Top of page. SUPPORT CELLS of nervous tissue. Schwann cells -- Support cells in peripheral nerves. Schwann cells form the myelin around myelinated peripheral axons. Schwann cells also envelop unmyelinated axons, but without the dense membrane wrapping which characterizes myelin.

Many of the small, heterochromatic nuclei that can be seen within peripheral nerves belong to Schwann cells. Some of the remaining nuclei belong to fibroblasts of the endoneurium, perineurium, and epineurium (i.e., connective tissue) that gives tensile strength to the nerve.

Perineurium also contains squamous perineural cells ( perineural epithelium) which form a continuous layer that isolates the axons within from surrounding connective tissue. Fibroblast nuclei tend to be smaller and more densely heterochromatic than Schwann cell nuclei, but in most ordinary preparations that include peripheral nerves, it is impractical to distinguish these nuclei. Note that none of the nuclei visible in peripheral nerves belong to nerve cells, since peripheral nerves do NOT contain nerve cell bodies, only axons of nerve cells whose cell bodies lie elsewhere. Support cells in peripheral ganglia are sometimes called satellite cells. Schwann cells can form tumors called schwannomas (see Web Path: MRI, gross, dissection, microscopic low X, high X ). Top of page. Glial cells -- Support cells of the CENTRAL NERVOUS SYSTEMThe most numerous cells within the central nervous system are glial cells.

The name ""glia"" means ""glue"" (filling the interstices of nervous tissue), reflecting old but enduring ignorance of their function (and the inadequacy of classical histology to offer much insight). The small nuclei of glial cells may be readily observed in any section of central nervous tissue. Unfortunately, like neurons, these cells are difficult to visualize satisfactorily. Although glial cells vastly outnumber nerve cells (approx. 10:1 glia to neurons), nerve cells are so large, including the total volume of all their dendrites and axons, that most of the cellular volume of the brain consists of nerve cells.

Ignorance of glial function is beginning to dissipate. For a recent review, see: Barres, BA (2008) The mystery and magic of glia: a perspective on their roles in health and disease. Neuron. 60 (3): 430-40 [Pub Med ID: 18995817]""In this perspective, [Barres] review [s] recent evidence that glial cells are critical participants in every major aspect of brain development, function, and disease.

Far more active than once thought, glial cells powerfully control synapse formation, function, and blood flow. They secrete many substances whose roles are not understood, and they are central players in CNS injury and disease. [Barres] argue [s] that until the roles of nonneuronal cells are more fully understood and considered, neurobiology as a whole will progress only slowly. """"And please don't forget the glia! Quite possibly the most important roles of glia have yet to be imagined.

""The two most common types of glia, oligodendroglia and astroglia, both have extensive cytoplasmic processes and are intimately involved in the function of nervous tissue. A third glial type, microglia, function similarly to macrophages. In most of our reference slides, both in the spinal smear and in sections of brain and spinal cord, only the nuclei of glial cells are clearly seen, with no indication of cytoplasmic shape.

The characteristic processes of glia can show up nicely in some of the Golgi-stained sections in your reference collection (variously cerebellum or cerebral cortex). Even with electron microscopy, it is difficult to trace CNS myelin to the arms of the oligodendroglia from which it forms. Separately distinguishing among astroglia, oligodendroglia and microglia is a skill for specialists (i.e., pathologists), but with practice their nuclei can be recognized by relative size and texture, with astrocyte nuclei being somewhat larger and paler than the others.

Oligodendroglia (also called ""oligodendrocytes"" or just ""oligos"") typically have relatively few processes (hence their name; oligo = few), with each process ending in a sheet of myelin which wraps around a segment of an axon. Function of oligodendroglia: Oligodendrocytes form myelin in the CNS and hence are responsible for normal propagation of action potentials .

Patchy loss of CNS myelin, as in multiple sclerosis ( Web Path, Web Path w/ MRI ), can cause a variety of neurological problems. Myelin formation by oligodendroglia is slightly different than that by Schwann cells, each of which wraps myelin around a single axon.

Each of the several glial cell processes extends to and then myelinates a segment of one axon. If the myelin of one oligodendrocyte process were unrolled, the process would be shaped rather like a wide-bladed shovel (the thin shovel blade would represent the membrane that rolls around the axon to form myelin and the shovel handle would represent the process which extends back to the glial cell body).

Each oligodendroglial cell has several such ""shovels"", forming myelin around several axons. Recent evidence from mouse, based on gene transcription profiles, indicates that oligos form several populations; for example, ""One population was responsive to motor learning, and another, with a different transcriptome, traveled along blood vessels"" ( Science 10 Jun 2016, 352:1288-1290, DOI: 10.1126/science.352.6291.1288-n). Astroglia or astrocytes extend branching cytoplasmic processes in all directions (yielding the star-like shape suggested by their name; astro = star).

Foot-processes of astrocytes line every surface where central nervous tissue contacts other body tissues, not only the obvious outer surface immediately underlying the pia mater (where they form the glia limitans) but also along every blood vessel and capillary which penetrates into the brain and spinal cord.

Other astrocyte foot processes approach nerve cells at any sites where the nerve cell membrane is not otherwise occupied by synapses or by oligodendroglia. Functions of astroglia: There is growing awareness that astrocytes play several critical roles. Recent evidence shows that activity of individual astrocytes can correspond closely with that of associated neurons, and can also modulate local blood flow ( Schummers, et al., Tuned responses of astrocytes and their influence on hemodynamic signals in the visual cortex, Science 320:1638-1643, 2008; doi:10.1126/science.1156120 ).

Additional functions and pathologies include all of the following ( from Ransom, et al., New roles for astrocytes (stars at last) Trends in Neuroscience, 26:520-522, 2003; doi:10.1016/j.tins.2003.08.006 ]:homeostasis, regulating concentrations of K +,extracellular p H, glutamate and water ;maintaining integrity of the blood-brain barrier;modulation of excitatory and inhibitory synapses;neuronal pathfinding during development and regeneration;glioma formation;cytotoxic brain edema;modulation of stroke outcome;hepatic encephalopathy;trophic modulation of neural repair and axon regrowth following injury.

Recent research also implicates astroglia in the "" glymphatic system "" which allows recirculation of CSF and brain interstitial fluid along paravascular channels. A 2013 report in Science 342:373 implicates this system in the function of sleep ( Science news article ). According to a 2016 news report in Science, ""Extracellular space takes up a large percentage of the brain.

Its size changes with the sleep-wake cycle but also during brain development and normal aging, as well as under pathological conditions such as neurodegeneration. Godin et al. injected near-infrared luminescent carbon nanotubes into rat brains and tracked their diffusion in the extracellular space.

This method revealed the dimensions of the extracellular space in live brain tissue. The extracellular space turned out to be a maze of interconnected compartments of multiple shapes that are structured in a wide range of different dimensions."" [The reference for this study is Nat. Nanotech. 10.1038/NNANO.2016.248 (2016). ]Microvascular control : Local variation in blood flow through brain capillaries may be regulated by activity of pericytes, which in turn can respond to neural activity. [ Reference: Mac Vicar & Salter, Neuroscience: Controlled capillaries, Nature 443, 642-643 (12 October 2006) | doi:10.1038/443642a .

]The Blood Brain Barrier"" Blood-brain barrier "" is the name given to a physiological property of CNS blood vessels. In contrast to vessels in most other parts of the body, most molecules can NOT pass freely between blood to interstitial space. The integrity of the blood-brain barrier is established by continuous capillary endothelium together with the absence of endothelial vesicular transcytosis.

The only substances which cross this barrier are those which can diffuse through endothelial plasma membranes or those for which specific endothelial membrane channels exist. The blood-brain barrier is a concept with considerable clinical significance, not only because it limits the delivery of drugs to the central nervous system but also because pathological disturbance of the barrier can seriously impact brain function.

Read a more extensive description of the anatomy and physiology of the blood-brain barrier at the University of Arizona Health Science Center, Blood Brain Barrier. The Blood Brain Barrier History of Blood-Brain Barrier Cell Membranes Pericyte, Astrocyte and Basal Lamina Association Anatomy and Physiology of the Cerebral Capillary Endothelia Transport at the Blood Brain Barrier Anatomy and Physiology of Blood-CSF Barrier Cerebral-Spinal Fluid Circumventricular Organs Blood Supply to the Brain Pathophysiology of the Blood Brain Barrier Microglia are small cells, comprising about 10% of the total brain cell population, which represent the brain's immune system (i.e., macrophage-equivalents residing within the brain).

Microglia are also implicated in the maturation, plasticity, and remodelling of synaptic circuits ( Science 333:1391, 9 September 2011, doi:10.1126/science.1212112; J. Neuroscience, 31:16064-69; doi: 10.1523/jneurosci.4158-11.2011)As described by Kembermann and Neumann (Microglia: the enemy within?

Science 302:1689, 5 December 2003, doi:10.1126/science.1092864 ), the brain exhibits ""a robust innate immune response thanks to its microglia, which defend against invading microorganisms and clean up by engulfing the debris of dying cells. In addition, the inflammatory mediators released by microglia during an innate immune response strongly influence neurons and their ability to process information.""

Recent in vivo observations (Fetler and Amigorena, Brain under surveillance: the microglia patrol, Science 309:392-3, 15 July 2005, doi:10.1126/science.1114852) show microglia as surprisingly dynamic cells, continually extending and withdrawing fine motile cellular processes and contacting astrocytes, neurons, and blood vessels. Recent research indicates that microglia (in mice) are ""an ontogenically distinct population in the mononuclear phagocyte system,"" originating during embryonic development ( Science, published online October 21, 2010; DOI: 10.1126/science.1194637)Top of page.

Blood vessels in CNSCentral nervous tissue is highly vascular, so blood vessels should be a significant feature in any histological specimen of CNS.

Large vessels generally remain on the surface of the brain or spinal cord, so only smaller vessels penetrate into gray and white matter. Such small vessels may not be immediately recognizable as such. As in other regions of the body, capillaries may be quite inconspicuous due to small size.

Even venules and arterioles may be small enough that the layers in their walls are not clearly visible. Blood cells may be washed out during preparation. Nevertheless, such vessels should be noticed, since they play a crucial role in brain function and pathology.

(Also see note on microvasculature, above. )Blood vessels are generally the largest structural elements in neuropil and in white matter (i.e., even capillaries are larger in diameter than most CNS axons and dendrites).

The thumbnails below link to several spinal cord specimens in which blood vessels may be observed. Blood vessels appear similar in any region of the brain. Note that a clear ""halo"" commonly appears around blood vessels (as well as neuronal and glial cell bodies). This an artifact of histological preparation, resulting from tissue shrinkage when the central nervous tissue is fixed. Top of page. Ependyma, choroid plexus and cerebro-spinal fluid The ventricular system of the brain is lined by a simple cuboidal epithelium called ependyma, a remnant of the embryonic neuroectoderm which once formed the neural tube.

At certain sites (the posterior margin of the lateral ventricles, the midline of the 3rd ventricle, the roof of the 4th ventricle), this ependyma lies adjacent to overlying connective tissue.

Here the ependyma is extensively wrinkled, with blood vessels which are caught up in the folds, to form choroid plexus. Choroid plexus is the source for cerebrospinal fluid (CSF). CSF is actively secreted by the ependymal cells of choroid plexus and (like aqueous humor in the eye) accumulates at a steady rate even if drainage points become occluded.

In composition, CSF differs considerably from blood. Although osmolarity and sodium concentrations are similar in blood and CSF, CSF has somewhat more chloride; less potassium, calcium, magnesium and glucose; much less protein, and practically no white blood cells. For specific values as wells as alterations in disease, see Kandel et al., 4th edition, Appendix B, especially pp.

1295-1299. CSF and brain interstitial fluid are exchanged through the so-called "" glymphatic system "" of paravascular channels. A 2013 report in Science 342:373 implicates this system in the function of sleep ( Science news article ).

The layout of choroid plexus is perhaps most easily appreciated embryologically -- click on the thumbnail for an image of embryonic choroid plexus. Cerebrospinal fluid accumulates not only from the action of choroid plexus but also from the interstitial spaces of the brain. It flows, under positive pressure developed by its active secretion, through the ventricular system, thence out through holes in the roof of the 4th ventricle into the subarachnoid space, finally draining through "" arachnoid villi "" into the venous sinuses of the cranial cavity.

Top of page. Meninges: dura mater, pia mater, and arachnoid The central nervous system is enveloped by specialized layers of connective tissue. The outermost layer is the dura mater (or just ""dura""), very dense fibrous connective tissue, tough and fairly impermeable.

Immediately adjacent to the brain is the pia mater (or just ""pia""), a delicate layer of collagen and fibroblast-like cells that adheres closely to the underlying glia limitans (the outermost layer of proper nervous tissue). In between dura and pia is the arachnoid, a layer of very loose connective tissue in which cerebrospinal fluid occupies the position of ground substance.

The name ""arachnoid"" presumably refers to the spidery, or delicately web-like, network of collagen fibers which extend through the arachnoid layer from dura to pia. Pia and arachnoid are not distinct, separate layers; together they are sometimes called ""pia-arachnoid"". The fluid-filled spaces of the arachnoid layer are sometimes called the ""subarachnoid space"". However, in spite of the "" sub -"", this space is within the arachnoid layer.

The dura which overlies cerebral venous sinuses is perforated by small passageways called ""arachnoid villi"" or ""arachnoid granulations"", which are sites where cerebrospinal fluid drains from the subarachnoid space into venous blood.

Top of page. SOME EXAMPLES of nervous tissue. This section offers a guide for microscope lab (i.e., for viewing slides in your reference set). Spinal smear Spinal cord section Cerebral cortex Cerebellar cortex Peripheral ganglia Retina Also see: Link to LUMEN (Loyola University Medical Education Network), click on ""Part 6: Neural Tissue"".

Link to Blue Histology . Click on ""Notes"", then ""Nervous Tissue"". Spinal cord smear Using your reference slides, the best view of ""whole"" neurons is provided by the slide labelled ""nerve cells, ox spinal cord"". (This is a slide of spinal smear, not a slice but a small amount of gray matter squished onto the slide. )Each spinal neuron displays classic nerve cell characteristics --.prominent cell body,distinctive round euchromatic nucleus,single prominent nucleolus,cytoplasm with basophilic masses of Nissl substance (rough endoplasmic reticulum). The largest nerve cells in this preparation represent spinal motor neurons, the cells whose very long axons extend out peripheral nerves to the muscles.

From the nerve cell body extend several dendrites; these are broad at their base and contain Nissl but decrease in diameter and basophilia with increasing distance from the soma.

The full extent of the dendritic arborization is not visible, since the fine distal branches are hidden in the background texture of the slide. Each neuron also has a single axon, which can be readily identified only if it begins on the edge of the cell body (as opposed to the top or bottom, as viewed in the slide).

The axon, unlike the dendrite, has a uniform diameter and does not contain basophilic Nissl bodies. It begins at the axon hillock, a specialized site on the cell body where the cytoplasm is clear (like the axoplasm, it lacks Nissl bodies). The axon, even more so than the dendrites, disappears into the distance and cannot be followed to its end.

In this same preparation, smaller cells with similar features represent spinal interneurons. Scattered throughout this preparation are also very many cells whose nuclei are smaller than those of the neurons, oval with clumps of heterochromatin, and whose cytoplasm is inconspicuous.

These are the glial cells. Numerous capillaries, narrow tubular profiles wandering across the slide, may also be seen. Spinal cord section The spinal cord consists of ascending and descending axonal pathways (i.e., white matter) surrounding a central core of gray matter .

Use your preferred neuro text to rehearse the functions associated with the following regions in the spinal cord. The dorsal horns are the narrow ""bands"" of gray matter which extend to surface on the dorsal, or posterior, aspect of the cord. The ventral horns are the broader ""regions"" of gray matter which do not reach to the surface. The conspicuous nerve cell bodies in the ventral horn belong to spinal motor neurons.

Dorsal columns are the white-matter fiber tracts between the dorsal horns. Lateral and anterior columns are the white-matter fiber tracts which wrap around the sides and front of the cord.

The central canal is the small channel (which may be occluded) in the gray matter which connects the gray matter of left and right sides. Spinal motor neurons are lost in amyotrophic lateral sclerosis (ALS) -- for more, see: Web Path (ALS, gross)Web Path (ALS, neuron loss)Web Path (ALS, gliosis). Some sections of spinal cord may include dorsal and ventral roots containing (respectively) sensory and motor axons.

Sensory axons in a sensory (dorsal) root enter the cord at the dorsal horn. Cell bodies of sensory axons occur in dorsal root ganglia, located near the cord along the dorsal root. Cell bodies of sensory axons occur in dorsal root ganglia, located near the cord along the dorsal root.

Motor axons in a motor (ventral) root originate from motoneuron cell bodies in the ventral horn and pass through white matter before leaving the cord. Cerebral cortex The cerebral cortex forms the surface of gyri an sulci over each entire cerebral hemisphere.

Its composition is complex (after all, it is the seat of conscious perception and thought! ), with many different types of nerve cells . These include many local interneurons ( stellate cells and granule cells) as well as the much larger and more conspicuous pyramidal cells, some of whose axons enter the underlying white matter and travel to other cortical areas or to other regions of the brain.

The cerebral cortex is traditionally (but rather arbitrarily) described as having six layers . Although these layer cannot be readily distinguished (they are arbitrary, after all), they can be roughly approximated by looking for the following features.

Layer I (the ""molecular layer"") is the outermost layer. This layer contains relatively few nerve cell bodies. The odd name ""molecular layer"" derives from the fine texture of this layer, due to its composition largely of dendrites and fine axon terminals (and glia, of course).

Layer II (the ""outer granular layer""), typically contains many very small cells ( granule cells ). Layer III (the ""outer pyramidal layer"") contains cell bodies of small pyramidal cells. Axons from these cells typically project to the upper layers of neighboring cortical regions. Layer IV (the ""inner granular layer"") contains axonal ramifications of afferent fibers, such as sensory axons from the thalamus.

Axons from the lateral geniculate nucleus (the visual relay of the thalamus) are so numerous that the primary visual cortex which receives these axons (Brodmann's area 17, at the occipetal pole of each hemisphere) is sometimes called ""striate cortex"", because these axons conspicuously divide the cortex into layers that are visible to gross inspection.

Layer V (the ""inner pyramidal layer"") contains cell bodies of large pyramidal cells. Axons from these cells typically project to more distant cortical regions, to other parts of the brain, or to lower centers (such as spinal motor neurons). The larger size of these pyramidal cells (compared the the smaller cells of layer III) is associated with the greater length of their axons.

(Recall that cell bodies provide most of the basic cellular functions needed to maintain the axon, while the axonal surface membrane and axoplasmic volume may be many times greater than the surface and volume of the cell body. )Layer VI (the ""layer of pleiomorphic cells) typically contains cells of assorted size and shape (hence, ""pleiomorphic"").

Variations in the detailed appearance (""cytoarchitecture"") of the several cortical layers, as described a century ago by K. Brodmann, formed the original basis for recognizing regional differentiation of the cortex ("" Brodmann's areas ""). Now, of course, this cytoarchitectural differentiation is known to correspond with functional localization in the cortex.

See Web Path for cortical changes associated with Alzheimer's disease. Cerebellar cortex The cortex of the cerebellum consists of three very well-defined layers. The most prominent nerve cells are Purkinje cells, whose cell bodies all lie in a discrete layer. The inner granular layer is packed with nuclei of vastly many cerebellar granule cells .

These are among the smallest (and most numerous) neurons in the body. The Purkinje cell layer contains large cell bodies of Purkinje cells, the sole output cells for the cortex. The outer molecular layer consists principally of the dendrites of Purkinje cells and the axons of granule cells.

The odd name ""molecular layer"" derives from the fine texture of this layer, due to its composition largely of dendrites and fine axon terminals. Nuclei in this layer belong mostly to glial cells. The pattern of connections among various axons and dendrites in the cerebellum is extremely elegant and regular, and has been described in extensive detail.

Any thorough neuro text (e.g., Kandel et al., 4th ed., pp. 835 ff) should have a good account. Peripheral ganglia Both the paravertebral ganglia of the sympathetic nervous system and the scattered ganglia of the parasympathetic nervous system consist of small clusters of nerve cell bodies. Parasympathetic ganglia may turn up in sections of various visceral organs, where they can be recognized by the classic appearance of nerve cell bodies.

Retina Tissues of the eye are listed in a separate page. Composition and appearance of PERIPHERAL NERVESLike other ""pieces"" of the nervous system, peripheral nerves are a part of a functioning, highly organized whole. Each ""piece"" must be understood in relation to the rest of the system. Examples of peripheral nerves are often fairly easy to find in sections of the skin .

Larger nerves also often run in parallel with blood vessels. Images which include examples of peripheral nerves. Click on a thumbnail below for enlargement. Peripheral nerves consist of axons bundled together within an epineurium (connective tissue sheath). Peripheral nerves are only meaningful in relation to their connections. All of the axons which travel along peripheral nerves begin and end somewhere else.

Motor axons originate with cell bodies in the spinal cord's ventral horn or in the brainstem's motor nuclei or in peripheral sympathetic or parasympathetic ganglia. Motor axons terminate at muscles (including smooth muscle along blood vessels) or glands. Somatosensory axons begin with a peripheral receptor (e.g., a Meissner's corpuscle in skin or a muscle-spindle in a muscle).

These sensory axons then travel toward their cell bodies in a dorsal root ganglion or trigeminal ganglion, and finally terminate at synapses within the spinal cord or brain stem. (Note that somatosensory axons are an exception to the rule that axons always conduct impulses away from the cell body.

)All the cellular nuclei which are obviously visible within a peripheral nerve belong not to nerve cells but to Schwann cells or to fibroblasts. In routine H&E slides, peripheral nerves resemble other fibrous tissues like smooth muscle or collagen.

All three are eosinophilic, and all contain scattered, elongated nuclei. Several features may be used to distinguish nerves from smooth muscle or other fibrous tissue. Nerves have a sheath of fibrous connective tissue, the epineurium, that forms a discrete boundary around the nerve.

Small nerves, and bundles of axons within large nerves, are also ensheathed by perineurium, including squamous cells ( perineural epithelium) whose intercellular junctions isolate the axons from surrounding connective tissue. The epineurium gives surgeons something to hold onto and stitch through when trying to reattach nerve ends while replacing a severed limb. Unless specially stained, nerve fibers tend to appear rather pale. Neither myelin (which is mostly fat) nor axoplasm (which is mostly water) is readily stained by H&E. Nerves often have a characteristic swirled or wavy texture, because axons in the nerve tend to twist, like fibers in a string.

Axons need to be somewhat longer than the nerve within which they run, so that if the nerve is stretched the axons do not all snap. The nuclei found within nerves are mostly Schwann cell nuclei. Schwann cell nuclei are usually larger and with less-condensed chromatin than fibroblast nuclei. A small bundle of smooth muscle can resemble a nerve, but has no sheath and is with commonly used stains is typically colored more intensely than nerve.

In longitudinal section, smooth muscle nuclei typically appear considerably longer than either Schwann or fibroblast nuclei, and in cross section of well-prepared specimens these nuclei can usually be seen to reside within the fibers (unlike either Schwann cell or fibroblast nuclei, which lie alongside the associated fibers).

Note that the texture of peripheral nerves can differ from site to site, depending on axon size and especially on the proportion of myelinated to unmyelinated axons. Nerves in the tongue, with many large myelinated axons, are much more obvious than are autonomic nerves in Auerbach's plexus of the gut, where most axons are smaller and unmyelinated. In peripheral nerve cross sections stained for myelin, the myelin is generally visible as a dark or black frame around each pale myelinated axon.

The typical round shape is often distorted by tissue preparation. In longitudinal sections containing large myelinated axons, nodes of Ranvier can be easily seen where the myelin appears to be ""pinched"".

Seldom can a single axon be followed throughout an entire internode (i.e., the segment of myelin from one node to the next, about 1-2 mm); the axon is just not straight enough to remain within the plane of section. Nevertheless, the length of each internode can be estimated by measuring the total length of all axons visible in a field of view and dividing by the number of nodes that appear.

In ordinary H&E stained cross sections of peripheral nerve, myelin is generally visible as a pale unstained halo around the axon. Less-than-ideal fixation also often distorts the relationship, so the axon may not be centered within the halo Many details of peripheral nerves cannot be well-appreciated by light microscopy. For electron micrographs of peripheral nerves, see the online Electron Microscopic Atlas of Mammalian Tissues (the text is in German, but most figure labels can be deciphered fairly easily).

SENSORY and MOTOR NERVE ENDINGS associated with PERIPHERAL NERVESFor sensory receptors in skin, see skin innervation. For sensory receptors associated with muscle, see muscle innervation. For motor endings on skeletal muscle, see muscle innervation. Composition of CENTRAL NERVOUS SYSTEMThe organization of the central nervous system is based upon interconnections across varying distances among billions of individual nerve cells.

The basic principle of neural organization is quite straightforward. Nervous tissue consists of nerve cells communicating with other nerve cells. This simple yet fundamental concept can easily become lost in the forest of details presented in standard textbooks. Here, then, is a brief guide to nervous tissue, including the classification and nomenclature of nerve cells.

Gray Matter and White Matter (Cortex, Nuclei, and Fiber Tracts)Each nerve cell has a cell body in one place and an axon which travels some distance to synapse with the cell bodies and dendrites of other neurons.

Regions consisting of cell bodies together with their associated dendrites and axon terminals are termed gray matter. Gray matter located on the surface of the brain is called cortex (e.g., cortex of the cerebral hemispheres, cortex of the cerebellum).

Masses of gray matter located deeper in the brain are called nuclei . (e.g., brainstem nuclei, nuclei of the thalamus). Regions consisting of axons gathered into bundles, to the exclusion of cell bodies, are called white matter.

White matter in which all of the axons lie parallel to one another is called a fiber tract. A fiber tract which crosses the midline to connect bilaterally symmetric structures is called a commissure. The microscopic appearances of gray matter and white matter may be conveniently contrasted in a section of spinal cord.

Various stains have various effects on gray matter. Note that a popular neuroanatomical stain (Weigert's), used to highlight different brain regions, colors myelin black. Thus, paradoxically, in many pictures of the brain, white matter appears black while gray matter appears pale. Gray matter: Where cell bodies and dendrites are common, the gross color of fixed (dead) brain tissue is gray.

Hence we have the term gray matte r. Note that gray matter is not just a place where cell bodies and dendrites happen to be. Gray matter is the cell bodies and dendrites. Living gray matter is not gray but rather pink, due to blood perfusing through very numerous brain capillaries.

(The brain is intensely vascular, with each cubic centimeter of brain tissue having around 100 square centimeters of capillary endothelial surface area. )Cortex is gray matter found on the surface of the brain. There is cerebral cortex covering the surface of cerebrum and cerebellar cortex covering the surface of the cerebellum.

But not all gray matter is cortical. A nucleus is a mass of gray matter found deep in the brain. Such nuclei are not to be confused with nuclei of individual cells, although neuron cell bodies with their cell-nuclei are found in brain-nuclei (and not in white matter).

Note that gray matter necessarily contains both the beginnings and endings of axons, even though the greater portion of many axons' length is contained within the fiber tracts of white matter. Gray matter is gray not because it lacks myelin, but because it contains lots of other stuff besides myelinated axons.

White matter: Axons from many different neurons often gather together in large numbers at some distance from their cell bodies. In such regions, the relatively large amount of myelin confers a white color, hence, white matter. Myelin is largely fat, which is white in both living and fixed condition. White matter represents axons going relatively long distances.

It is the stuff of "" fiber tracts "" or "" pathways "". If white matter is cut, the cell body at one end of each axon is disconnected from its distal axon terminals at the other end. In some white matter areas most axons are travelling in parallel, with all action potentials propagating in the same direction.

For example, most axons in the dorsal columns are ascending, while those in the cortico-spinal tract are descending. But in many other white matter regions of the CNS, adjacent axons may carry signals in opposite directions or be interwoven in a complex meshwork. For example, axons in the internal capsule and corpus callosum crisscross back and forth, interconnecting many different regions of the cerebral hemispheres.

Note that although white matter consists of myelinated axons (and unmyelinated axons as well), myelinated axons are not excluded from gray matter. Myelinated axons must begin and end somewhere, and that place is with cell bodies and dendrites of gray matter. Gray matter just has a lot of other stuff in it besides myelinated axons. Also note that in many neuroanatomical images, white matter has been stained black.

Sensory Neurons, Motor Neurons, and Interneurons Sensory neurons convey sensory information into the central nervous system. Primary sensory neurons receive their information directly through sense receptors rather than dendrites. Second, third and higher order sensory neurons relay information to sequentially higher levels in the brain. Motor neurons (or motoneurons) convey information out from the central nervous system to muscles or glands. Lower motor neurons, located in the ventral horn of the spinal cord or in motor nuclei of the brainstem, send their motor axons out peripheral nerves.

Upper motor neurons, pyramidal cells located in the motor cortex, relay information to the lower motor neurons. All other neurons are interneurons. They interconnect neurons with other neurons. Nearly all the nerve cells in the central nervous system are interneurons. Their axons arise in one region of the CNS where the cell body resides and end somewhere else (sometimes several other places).

Second, third and higher order sensory neurons can be considered as ascending interneurons; upper motor neurons can be considered as descending interneurons. Synaptic Relays Information from primary sensory neurons does not reach the highest levels (the cerebral cortex) directly. Rather it is relayed at least twice (once in the spinal cord or brain stem, again in the thalamus ). At each relay, incoming ( afferent, presynaptic) axons terminate by synapsing onto the dendrites of the next neurons in the series.

The outgoing axons of these neurons then relay the information to the next level. At each relay site, some information processing and distribution can occur, so the information can be altered as it travels upward.

Similarly, muscle commands are relayed downward from motor cortex and other motor centers to the "" final common pathway "", the lower motor neurons of cranial nerve nuclei and the anterior horn of the spinal cord. Because each relay occurs at synapses onto dendrites and cell bodies of the next neurons in the pathway, each relay is associated with gray matter.

Conversely, every gray matter region (nucleus or cortex) is associated with relaying information from one set of axons (the afferent axons that enter the region in question) to another (the efferent axons that leave the region). Sometimes it is sufficient just to know the beginning and ending points of an entire pathway. Other times knowing how far the neurons of each relay extend will be necessary to determine the site or effects of a lesion.

Afferent and Efferent Axons All gray matter regions of the brain, both cortex and nuclei, are associated with afferent (""input"") and efferent (""output"") axons. Afferent axons enter the region from somewhere else (i.e., the cell body is located some distance away.) Efferent axons arise from cell bodies within the region and leave the region to go somewhere else. Thus every long-distance axon is both efferent (with respect to its source, the location of its cell body) and afferent (with respect to its destination).

The terms ""afferent"" and ""efferent"" are relational terms. Neither can be used precisely without specifying a region of reference (e.g., ""cortical afferents"" provide input to cortex; they may be efferents from thalamus or efferents from some other cortical area. )Ascending and Descending Pathways""Ascending"" and ""descending"" refer to directions along the neural axis.

These terms may often correlate with "" afferent "" and "" efferent "", at least when the reference is high, like cortex. (In fact, ""afferent"" and ""efferent"" are sometimes used as synonyms of ""ascending"" and ""descending"", respectively.

But they also have a relational meaning, defined above .) ""Ascending"" and ""descending"" are also closely associated with ""sensory"" and ""motor"", respectively. But both sensory and motor information can be passed up, down, and sidewise, so these words should not be carelessly interchanged.

Long-Axon And Short-Axon Neurons Gray matter typically contains both many short-axon neurons and a smaller number of long-axon neurons. The largest and most conspicuous cell bodies in a particular region of gray matter are sometimes referred to as the principal cells of that region. These cells generally have very long axons which leave the local region to go elsewhere, usually traveling within some white matter fiber tract.

The axons of these projection neurons may extend for appreciable distances, from a few centimeters to well over a meter. Long-axon neurons are responsible for communicating with other brain regions. Every parcel of gray matter has a class of long-axon neurons; otherwise information would come in but never go out.

The axons of a region's long-axon neurons are by definition identical with the region's efferent axons. Such large, long-axon cells may have specific names like pyramidal cells (the output cells of the cerebral cortex) or Purkinje cells (the output cells of the cerebellar cortex).

A large cell body is probably necessary to support the volume of cytoplasm contained within an extremely long axon. For exercise, estimate the volume of axoplasm in an axon 5 �m in diameter and ten centimeters long.

Compare that result with the volume of cytoplasm in a cell body 50 �m in diameter. The study of neuroanatomy is largely the study of the axonal projections of long-axon cells.

The axons of the short-axon neurons do not leave the immediate neighborhood. Short-axon neurons are also called intrinsic neurons or local interneurons. Short-axon neurons are presumably responsible for integrating information from diverse sources. (""Integration"" is the jargon term for what nervous tissue does when it transforms information, or thinks.

It provides a convenient name for a process that is otherwise poorly understood. )Cell bodies of short-axon neurons are often small and numerous. They come in various shapes, and are given names according to the region where they are round (see neuron names, below).

Most so-called granule cells and stellate cells are local interneurons. In most regions, long-axon cells are much better understood than intrinsic cells. Long axons provide opportunity for researchers to record and interfere with neuronal output. Cells with short axons are much more difficult to manipulate. Neuron Names Neurohistology is burdened by a profusion of names for different neuronal cell types.

Every nerve cell can be classified according to its place within the general organization of nervous tissue (above). But every nerve cell also belongs to a unique population with a particular role in the information processing of the brain.

Unlike most other basic cell types in the body (e.g., epidermal cells or fibroblasts), nerve cells are not all equivalent to one another. Neurons in one region are structurally and functionally different from those in other regions, with different sources of input, different destinations for output, different patterns of dendritic branching, different neurotransmitters, etc.

The result is a tremendous abundance of nerve cell types, with specific names for each. A few examples follow. Neuron preparation by Ramón y Cajal Pyramidal cells are the efferent (long-axon) cells of the cerebral cortex.

The name refers to the shape of the cell body as seen in standard sections perpendicular to the cortical surface. The apex of the pyramid points toward the cortical surface. A large apical dendrite extends further upward toward that surface, while other dendrites arise from the corners and sides of the pyramid.

The axon extends down into white matter (the internal capsule) from the base of the pyramid. Most pyramidal cells project association fibers to other cortical regions and/or to deeper nuclei of the brain. (Classic illustrations of these cells were done by Ramón y Cajal ). The giant Betz cells are extremely large pyramidal cells of the motor (precentral) cortex.

These pyramidal cells comprise some of the upper motor neurons. Axons from these cells descend in the corticospinal tract, or pyramidal tract, to synapse with lower motor neurons. Their exceptionally large size is presumably associated with their need to sustain extremely long axons. Stellate cells are intrinsic neurons named for their star-like shape, which results from dendrites arising in many directions.

The name is descriptive but relatively non-specific. Thus stellate cells of the cerebral cortex are not the same as stellate cells of the cerebellar corte x. Horizontal cells are intrinsic neurons whose dendrites and local axons tend to be confined within a layer parallel to a surface.

Again the name is descriptive rather than specific. Thus horizontal cells in the cerebral cortex are not the same as horizontal cells in the retina. Granule cells are intrinsic neurons which are both very small and very numerous, like grains of sand. Once again, this name is descriptive but non-specific unless additionally qualified. For example, cerebellar granule cells are a very specific class of short-axon cells in one layer of the cerebellar cortex (a layer called, unimaginatively, the ""granule cell layer"").

Purkinje cells are the efferent (long-axon) cells of the cerebellar cortex. Purkinje cells have such impressive dendritic arborization, that images of these cells (often from the classic illustrations of Ramon e Cajal) are often featured in textbooks.

The synaptic input of Purkinje cells comes largely from the cerebellar parallel fibers (which are the axons of the extremely numerous local interneurons, the cerebellar granule cells). Purkinje cells also receive potent synapses directly from one class of cerebellar afferent fibers, the ""climbing fibers"".

(Another class of cerebellar afferents, the ""mossy fibers"", provide input to the intrinsic granule cells. In addition to Purkinje cells and granule cells, the cerebellar cortex also contains stellate cells, basket cells, and Golgi cells.) [ See your favorite neuro text (e.g., Kandel et al., 4th ed., pp. 835 ff) for elegant details of neural circuitry in the cerebellar cortex.

]Spinal motor neurons have the largest nerve cell bodies in the ventral horn. These cells are also called ""lower motor neurons"", or just ""motor neurons"" (since upper moter neurons are properly called interneurons).

Axons of these cells extend through ventral (anterior) roots into peripheral nerves, and hence to motor end plates on muscle fibers.

Each muscle fiber of skeletal muscle is innervated by a single spinal motor neuron. Each spinal motor neuron innervates one or more muscle fibers; the number of muscle fibers per axons is related to the fineness of motor control -- e.g., one-to-one for eye muscles, many-to-one for large postural muscles. A single spinal motor neuron and all the muscle fibers innervated by its axon are called a motor unit. Spinal motor neurons are lost in amyotrophic lateral sclerosis (ALS) -- for more, see: Web Path (ALS, gross)Web Path (ALS, neuron loss)Web Path (ALS, gliosis).

The above are only examples. Every region of the central nervous system contains many distinct neuronal cell types, most of which are appreciated only by the research specialist.

But a few examples are worth knowing, both because they are a part of familiar scientific knowledge and because they illustrate the complexity of neural organization. Note that in every region the long-axon cells are directly associated with significant neuroanatomical pathways (output), while detailed knowledge of the intrinsic cells generally has little clinical importance (at least in our current state of ignorance).

NERVOUS TISSUE PATHOLOGY. Chapter 18 in the 3rd edition of Kandel et al. (1991) is an excellent resource for understanding the responses of nervous tissue to injury.

The newer, 4th edition of Kandel et al. (2000) offers a much sketchier account in Chapter 55 (pp. 1108 ff). Washington University hosts an excellent web resource for neuromuscular pathology. Within this site, you can find: Differential Diagnosis for neuropathy,Many pathology images,And much more. Web Path also offers some examples of nervous system pathology, see Web Path CNS Pathology Index and Web Path CNS Degenerative Diseases. For example: Spinal motor neurons are lost in amyotrophic lateral sclerosis ( Web Path , gross; Web Path, neuron loss; Web Path, gliosis).

Alzheimer's disease ( Web Path ) is accompanied by cortical changes ( Web Path gross, Web Path, Web Path, Web Path, Web Path,, Web Path, Web Path ) . Inflammation, as in meningitis ( Web Path ), presents infiltration of leukocytes into regions, such as CSF, where they are normally absent. Multiple sclerosis ( Web Path, Web Path w/ MRI ) involves patchy loss of CNS myelin, apparently caused either by autoimmune destruction of oligodendroglia or by malfunction of oligodendroglia with immune destruction as a secondary effect ( Science 308:778, 2005).

Resulting loss of conduction can cause a variety of neurological problems. ""Microscopically, the caudate nucleus in Huntington's disease demonstrates loss of neurons along with gliosis"" ( Web Path, gross; Web Path , microscopic).

Parkinson's disease ( Web Path ) involves loss of the pigmented neurons in the brainstem which give substantia nigra (""black substance) its distinctive appearance. Brain tissue in CJD or Creutzfeldt-Jakob disease ( Web Path, Web Path, Web Path ) is characterized by microscopic vacuoles (hence, ""spongiform encephalopathy"") and plaques. Schwann cells can form tumors called schwannomas (see Web Path: MRI, gross, dissection, microscopic low X, high X ). Online slides of the nervous system -- normal | pathology These specimens at the Virtual Slidebox (University of Iowa Department of Pathology) may be examined with full range of magnification and movement. Requires Java and fast internet connection . Comments and questions: dgking@siu.edu SIUC / School of Medicine / Anatomy / David King http://www.siumed.edu/~dking2/ssb/neuron.htm Last updated: 28 December 2016 / dgk "

Action Potential Explained - The Neuron. An Action potential is the neurons way of transporting electrical signals from one cell to the next. This is a picture of a neuron, where you have dendrites in one end, and the axon terminal in the other end. In the middle of the neuron you will find the axon, which is where the electrical signal will travel from the dendrites to the axon terminal to the synapse.

Action Potential Explained - The Neuron

Action Potential Explained - The Neuron Bittersweet Biology Subscribe 2.9KAdd to Share More492,420 views2,513148Published on Jun 19, 2014

This is a picture of a myelinated neuron, which is covered with a myelin sheath that allows the electrical signal to travel faster through the axon. So instead of activating every ion channel down the axon, only channels in the small spaces between each myelin sheath called the Node of Ranvier is activated and generates an action potential.

So lets take a closer look at the axon. On the membrane of the neuron, you will find small ion channels that are closed when the cell is in its resting state.

The neuron is able to create an action potential because of the concentration difference of ions between the intracellular space and the extracellular space. There is a higher concentration of sodium ions outside the neuron and a higher concentration of potassium inside the neuron.

the extracellular space is more positive than inside the neuron. This creates a voltage difference of -- 70 m V, which is created with the help of leaky ion channels that are more permeable to potassium ions than sodium ions, which will cause potassium to leave the cell and only small amount of sodium to enter.

The sodium potassium pump also regulates the intracellular environment, by pumping out 3 sodium ions in exchange for 2 potassium ions. The -- 70 m V is the neurons resting potential, but when the neuron is stimulated by a presynaptic neuron, it causes sodium channels to open, letting in positive ions.

This will change the electrical environment and make it more positive on the inside and less positive on the outside. This is called Depolarization, and which causes a chain reaction where the next sodium channels will open letting in positive ions, all the way down the axon.

Shortly after a channels have opened, they will close again and potassium channels will then open letting out positive potassium ions, to recreate the negative environment inside the neuron and the positive environment outside. This happens at around + 40 m V, and causes a Repolarization where the intracellular space is becoming negative again.

The neuron then reaches a state of Hyperpolarization where the cell has let out too many ions and has now become more negative than the cells resting potential. This is quickly corrected by the leaky channels and the sodium potassium pump, and the neuron stabilize at the resting potential at a -- 70 m V. The action potential that has traveled through the axon, reaches the axon terminal, where vesicles with neurotransmitters are released out into the synaptic cleft to transport the signal to another neuron. Show more Loading...

the point of communication between two neurons-includes axon terminal of the sending neuron, the synaptic space (gap), and dendrites/cell body of the receiving neuron

AP Psychology Biological Basis

"89 terms jaquiwilson AP Psychology Biological Basis AP Psychology terminology for biological basis of psychology Learn Flashcards Write Spell Test Match Gravity Advertisement Upgrade to remove ads Like this study set?

Create a free account to save it. Create a free account Maybe later Sort Peripheral nervous system (PNS) division that connects the central nervous system to the rest of the body; divided into somatic nervous system and autonomic nervous systemneural impulse action potential; the firing of a nerve cell; the entire process of the electrical charge (message/impulse) traveling through inner on; can be as fast as 400 fps (with myelin) or 3 fps (no myelin)motor projection areas primary motor cortex; areas of the three boat cortex for response messages from the brain to the muscles and glandsendocrine glands the bodies ""slow"" chemical communication by secreting hormones directly into the bloodstreamsynaptic cleft synaptic gap or synaptic space; tiny gap between the terminal of one neuron and the dendrites of another neuron (almost never touch); location of the transfer of an impulse from one neuron to the nextparasympathetic division a branch of the autonomic nervous system that maintains normal body functions; it calms the body ever conserves energycerebral cortex 80% of weight of human brain; 70% of CNS's neurons; wrinkled outer portion of un-myelin aided cells (cerebrum) covering both hemispheres; processes thought, vision, language, memory, and emotions; most recently of all part of nervous systembehavioral genetics study of hereditary influences and how it influences behavior and thinking DNA deoxyribonucleic acid; genetic formation in a double-helix; can replicate or reproduce itself; made of genesacetylcholine (ACh) distributed widely throughout CNS; involved in arousal, attention, memory, motivation, and movement; involved in muscle action at neuromuscular joints (skeletal muscles); implicated in Alzheimer's disease-loss of memory and severe language problems; too much dopamine = spasms and tremors; too little dopamine = paralysis and torporinterneurons connection neurons; Association neurons that carry messages to another neuronserotonin ""mood molecule""; chemical that affects regulation asleep, dreaming, mood, hunger, pain, and aggressive behavior; and attaches to many receptors (receptor sites)dopamine chemical that influences voluntary movement, learning, pleasure, memory,-is implicated in Parkinson's disease and schizophrenia; in Parkinson's disease a causes tremors, muscle spasms, increasing muscular rigidity; recently implicated in ADHDoccipital lobe part of cerebral cortex that receives visual informationaxon Greek for axle; a single long, fluid-filled tube that carries outgoing messages to other neurons, muscles, or glands; can be 1 or 2 mm to 3 feet in length; often referred to as a nerve or tract; bundled togetherendocrine system the body slow chemical communication system which is made up of a set of glands that secrete hormones into the bloodstream; made of the glands-pineal, pituitary, parathyroid, thyroid, pancreas, and adrenal, ovaries and testesparathyroid for glands embedded in the thyroid; secretes parathormone; controls announces level of calcium and phosphate (which influence levels of excitability)reticular formation (RF) (RES) netlike system of neurons that weaves through limbic system and plays an important role in attention, arousal, and alert functions; arouses and alerts higher parts of the brain; anesthetics work by temporary shutting off RF systempituitary gland endocrine gland that produces a large amount of hormones; it regulates growth and helps control other endocrine glands; located on underside of brainfrontal lobe part of the cerebral cortex; coordinates messages from other cerebral lobes; involved in complex problem-solving tasks, thinking, self-control, judgment, emotion regulation, personality affects, concentration, goal directed behavior; restructures in teen yearshypothalamus small area of the brain that is part of the limbic system and regulates behaviors related to survival such as, eating, drinking, sexual behaviors, motivationneural plasticity Ability of the brain to change their experience, both structurally and chemicallyforebrain top of the brain which includes the thalamus, hypothalamus, and cerebral cortex; responsible for emotional regulation, complex thought, memory aspect of personalitybrainstem top of the spinal columngraded potential shift in electrical charge in a tiny area of the neuron (temporary); transmits a long cell membranes leaving neuron and polarized state; needs higher than normal threshold of excitation to firestrain studies studies of hereditability it be a behavioral traits using animals that have been inbred to produce strains that are genetically similar to one anotherfamily studies studies of hereditability on the assumption that if a gene influences a certain trait, close relatives should be more similar on that trait in distant relativeidentical twins twins from a single fertilized oval with the same genetic makeupepinephrine adrenaline; activates a sympathetic nervous system by making the heart beat faster, stopping digestion, enlarging pupils, sending sugar into the bloodstream, preparing a blood clot fasterhippocampus a curved portion of the forebrain structure that is part of the limbic system and is involved in learning and processing new memoriesneurogenesis production of new brain cells; November 1988: cancer patients proved that new neurons grew until the end of lifecerebellum ""little brain""; part of the brain that coordinates balance, movement, reflexeslimbic system a donut ring-shaped of loosely connected structures located in the forebrain between the central core and cerebral hemispheres; consists of: septum, cingulate gyrus, endowments, hypothalamus, and to campus, and amygdala; associated with emotions and memoriesautonomic nervous system a division of the peripheral nervous system that regulates involuntary functions; it takes a message from the central nervous system to the internal organsrelative refractory period a period after firing when a neuron is returning to its normal polarize state and will only fire again if the incoming message open parentheses impulse) is stronger than usual; returning to arresting stateinsulin hormone backpacks in the regulation of blood sugar by acting in the utilization of carbohydrates; released by pancreas; too much-hypoglycemia, too little-diabetessynaptic vesicles tiny oval-shaped sacs in a terminal of one neuron; assist in transferring mineral impulse from one neuron to another neuron by releasing specific neurotransmittersabsolute refractory period a.

After firing when a neuron will not fire again no matter how strong the incoming message may be; length-1000th of a secondnorepinephrine noradrenaline; chemical which is excitatory, similar to adrenaline, and affects arousal and memory; raises blood pressure by causing blood vessels to become constricted, but also carried by bloodstream to the anterior pituitary which relaxes ACTH thus prolonging stress responsedendrites the bushy, branching extensions of the cell body that receives messages and conducts impulses; Greek for treehuman genomes 30,000 genes needed to build a humantwin studies studies as identical and rhetorical twins to determine relative influence of heredity and environment on human behaviorendorphins chemical inhibiting the transmission of pain, often experienced during exercise, i.e.

""runner's high""; discovered in 1970s when trying to find out how opiates were (morphine, heroin); ""endorphins"" is a pharmacological (drug/med) termmyelin sheath a white, lipoid (fatty) material in casing many neuron fibers and enables faster transmission of an impulse; white matter; it's pinched at intervals; not on all neurons but found throughout the body; insulin to prevent interference from other neuronssympathetic division a branch of the autonomic nervous system and prepares the body for quick action in emergencies; fight or flight; busiest when frightened, angry, or aroused; increases heart rate, increases breathing rate, enlarges pupils, stops digestion; connects to all internal organs; sudden reactionions electrically charged particles found both inside and outside a neuron; negative ions are found inside the cell membrane in a polarized neuron Association areas areas of the cerebral cortex that are not involved in primary motor or sensory functions, rather, they are involved in higher mental processes such as learning, remembering, thinking, and speaking Genetics study of how traits are transmitted from one generation to the nextrecessive gene member of the gene that controls the appearance of a certain trait only if it is paired with the same genethyroid gland located in the net; it regulates metabolism by secreting two hormones: thyroxine and parathormonemidbrain the middle division of brain responsible for hearing and sight; location where pain is registered; includes temporal lobe, occipital lobe, and most of the parietal lobepolarization when the neuron is at rest; condition of neuron when the inside of the neuron is negatively charged relative to the outside of Enron; is necessary to generate the neuron signal in release of this polarizationresting potential when a neuron is in polarization; more negative ions are inside the neuron cell membrane with a positive ions on the outside, causing a small electrical charge; release of this charge generates a neuron's impulse (signal/message)glial cells Greek for glue; forms myelin sheath; holds neuron in place; provides nourishment and removes waste; prevents harmful substances from entering bloodstream; may play important role in memory and learning; affects brain's response to new experiencesdominant genes member of a gene terror that controls the appearance of a certain traitpons part of the brain involved in sleep regulation also connects a cerebellum to the cerebral cortex; sleep and wake cyclesthyroxine released by thyroid; hormone that regulates the body's metabolism; OVERACTIVE-over-excitability, insomnia, reduced attention span, fatigue, snap decisions, reduced concentration (hyperthyroidism); UNDERACTIVE-desire to sleep, constantly tired, weight gain (hypothyroidism)nerve bundles of axonschromosomes pair of threadlike bodies within the cell ; contains genessomatic nervous system division of peripheral nervous system; carries messages from afferent neurons central nervous system and between central nervous system to skeletal muscles; controls voluntary actionsgonads reproductive glands-male, testes; female, ovariesreceptor site a location on a receptor neurons which is like a key to a lock (with a specific nerve transmitter); allows for orderly pathwayspsychobiology study that focuses on biological foundations of behavior and mental processes; overlaps with neuroscience Central nervous system (CNS) the brain and spinal cord; 90% of the bodies neuronsmedulla part of the brain which controls living functions such as breathing, heart rate, blood pressure, body temperatureneuron 100 billion in brain; individual cells that are the smallest unit of the nervous system; it has three classes: efferent, afferent, and interneurons; made of Colin dendrites, axons, synaptic gap, terminal buttons, synaptic vesicles, and sometimes myelinselection studies studies that estimate the hereditability of a trait by breeding animals with another animal that has the same trait (beta) endorphins a natural painkiller released by the body, often experienced during exercise; discovered in 1970s when investigating how opiates were; beta endorphins are naturalspinal cord a bundle of neuron axons which act like cables carrying messages to the PNS; connects brain to the rest of the body; wrapped in myelin and, surrounded and protected by vertebral bones; spinal injuries-paralysis, bowel/bladder control, low blood pressurehindbrain division which includes the cerebellum, Pons, and medulla; responsible for involuntary processes: blood pressure, body temperature, heart rate, breathing, sleep cyclesadrenal glands located above the kidney and secretes epinephrine and norepinephrine; stimulated by autonomic nervous systemmotor neurons efferent neurons; neurons that carry messages from spinal cord/brain to muscles and glandsneurotransmitters chemical messengers released by synaptic vesicles and travel through the synaptic gap assisting neural impulses (messages) as they leave one neuron to the next; affects adjacent neurons; examples: ACh, dopamine, serotonin, endorphins, and norepinephrine, glutamate, GABA, and glycineparathormone hormone that controls imbalances levels of calcium and phosphate in the blood and tissue fluid; influences levels of excitability; secreted by parathyroidsgenes elements that control transmission of traits; on the chromosomeshormones serves a function similar to neurotransmitters in that they carry messages; chemical messengers that travel through the bloodstream; manufactured by glands (mostly); help regulate bodily functionssynapse

pancreas organ lying between the stomach and small intestine; regulates blood sugar by secreting to regulating hormones: insulin and glucagonthalamus motor sensory relay center for four of the five senses; and with a brain stem and composed of two egg-shaped structures; integrates in shades incoming sensory signals; Mnemonic-""don't smell the llamas because the llamas smell bad""temporal lobe involved in complex visual tasks and processing; balance; emotional regulation and maturity; Strong oral and language comprehension; smell; hearing; still developing after age 16ACTH (arenocorticotropic hormone) released by adrenal glands; triggered by norepinephrine to prolong the response to stress (used in the sympathetic nervous system)polygenic inheritance process by which several genes interact to produce a certain trait; responsible for most important traitsparietal lobe part of the cerebral cortex never see sensory information from skin, muscles, joints, organs, taste buds; involved in spatial/visual abilities and integrates all sensory signals; immature until age 16amniocentesis collection of fetal cells and testing them for genetic abnormalities; using a long needle to withdraw cells from third trimester pregnant woman; uses amniotic fluid which surrounds fetus in the wombaxon terminal terminal button, synaptic knob; the structure at the end of an excellent terminal branch; houses the synaptic vesicles and neurotransmitterscorpus callosum large band of white neural fibers that connects to to brain hemispheres and carries messages between them; myelinated; involved in intelligence, consciousness, and self-awareness; does it reach full maturity until 20sneuroscience study of the brain and nervous system; overlaps with psychobiologysensory neurons afferent neurons; neurons that carry messages from sensory organs to the brain and spinal cordsfraternal twins two children developed on two separate eggs that share a room; no more genetically similar than other brother and sisters (i.e.

different genetic makeup) "

Dendrites receive nervous system signals through synapses, which form the connections between neurons where the axon terminal of one nerve cell ends near the dendrites of another nerve cell. Nerve cells do not physically touch each other.

What Do Dendrites Do?

"Science Human Anatomy Nerves Q: What Do Dendrites Do? A: Quick Answer Dendrites are a part of the central nervous system that receive input from nerve cells, which are sometimes called.

Multiple fibers called dendrites extend in a branchlike formation from the cell body of a neuron. When the postsynaptic terminals, or receptors, at the end of a dendrite receive neurotransmitters released by other neurons, an electric signal is transmitted through the dendrite to the cell body of the neuron.

Continue Reading Keep Learning What Is a Multipolar Neuron? How Many Nerves Do We Have in Our Bodies? What Is the Function of the Myelin Sheath? Credit: IONclad CC-BY 2.0Full Answer

Instead, they communicate through the use of neurotransmitters that travel across the space called the synaptic cleft between the cells. An electrical signal travels down one neuron's axon and triggers the release of chemical compounds called neurotransmitters.

Neurotransmitters move across the synaptic cleft and connect to the receptors on the other nerve cell. This triggers an electrical impulse that then travels from the dendrites to the cell body. The typical neuron has thousands of dendrites, but it is possible for a nerve cell to have only one dendrite. Dendrites are relatively short, and they have spines that provide more surface area for other neurons to synapse with.

Their branch-like formation inspired the name ""dendrite,"" which means ""tree"" in Greek. Learn more about Nerves Sources: neurogenesis.com science.education.nih.gov Related Questions Q: What Is the Function of the Motor Nerves? A: Motor nerves are bundles of nerve cells that control muscles. They originate in the spinal column and end at the muscles that they control.

One motor nerve... Full Answer >Filed Under: Nerves Q: What Is the Function of Nerve Cells? A: According to the BBC, the function of nerve cells is to transmit electrical messages and signals throughout the body.

There are three types of nerve cells.... Full Answer >Filed Under: Nerves Q: What Types of Tissues Make up the Brain? A: The brain is made up largely of neurons, or nerve cells, blood vessels and glial cells. Glial cells create a supporting structure for the brain.

The brain ... Full Answer >Filed Under: Nerves Q: What Are the Neurons That Carry Impulses Toward the Spinal Cord and Brain? A: Sensory neurons are the nerve cells which carry information from outside stimuli to the central nervous system, which includes the spinal cord and brain.

T... Full Answer >Filed Under: Nerves You May Also Like Q: What Makes up the Peripheral Nervous System? Q: What Is the Sensory Strip? Q: What Does the Somatosensory Cortex Control? Q: Which Part of the Brain Controls Breathing? Q: What Is the ""reptilian Brain? ""Q: When Is the Brain Fully Developed? "

An Axon Terminal is the very end of a branch of a nerve's axon, a long slender nerve fiber that conducts electrical signals to a nerve synapse (the gap between nerve cells).

Axon Terminal

Axon Terminal

The signal then moves across the synapse to another axon by means of a neurotransmitter (an electrochemical substance). Add flashcard Cite Random Word of the Day Get the word of the day delivered to your inbox

Axons often have thousands of terminal branches, each ending as a bulbous enlargement, the synaptic knob or synaptic terminal. At the synaptic knob, the action potential is converted into a chemical message which, in turn, interacts with the recipient neuron or effector. This process is synaptic transmission.

Synaptic Transmission

"Synaptic Transmission Follow City-Data.com founder on our Forum or @Lech Mazur Photo by: Alila Synaptic transmission is the process whereby one neuron (nerve cell) communicates with other neurons or effectors , such as a muscle cell, at a synapse.

A typical neuron has a cell body (soma), branching processes specialized to receive incoming signals (dendrites), and a single process ( axon) that carries electrical signals away from the neuron toward other neurons or effectors.

Electrical signals carried by axons are action potentials .

Synapses Synapses are junctional complexes between presynaptic membranes (synaptic knobs) and postsynaptic membranes (receptor surfaces of recipient neurons or effectors). The prefixes ""pre-"" and ""post-"" reflect the direction of synaptic transmission: presynaptic is the transmitting side (synaptic knob) and postsynaptic is the receiving side (dendrite, soma, or effector). Synaptic knobs contain many membrane-bounded synaptic vesicles , 40 to 100 nanometers in diameter. Synaptic vesicles contain the neurotransmitter. Synaptic knobs also contain mitochondria , microtubules, and other organelles .

Synapses are named according to their location on the postsynaptic neuron : Axospinous synapses are synapses on dendritic spines (tiny projections on the dendrites), axodendritic synapses are on shafts of dendrites, axosomatic synapses are on the soma of neurons, and axoaxonal synapses are synapses on other synaptic knobs.

Synapses on skeletal muscle cells are neuromuscular junctions. Neurotransmitter Release Action potentials arriving at synaptic knobs trigger the release of neurotransmitter into the synaptic cleft.

The molecular mechanism is not completely understood. A ""synaptic delay"" of one to two milliseconds occurs between the arrival of the action potential and the neurotransmitter release. Action potentials open calcium channels in the membrane of the synaptic knob, which causes an inward movement of calcium ions .

Calcium ions trigger the release of neurotransmitter from synaptic vesicles into the synaptic cleft. The synaptic vesicles fuse with the presynaptic membrane during this process of exocytosis. The membranes of old vesicles become part of the presynaptic membrane and new vesicles pinch off from an adjacent area of membrane.

These new vesicles are subsequently refilled with newly synthesized or ""recycled"" neurotransmitters . Released neurotransmitters diffuse across the narrow synaptic cleft. At the postsynaptic membrane, neurotransmitter molecules bind to membrane-bound receptor molecules with recognition sites specific for that neurotransmitter. Binding of the neurotransmitter to the receptor triggers a postsynaptic response specific for that receptor. These responses can be either excitatory or inhibitory, depending on the properties of the receptor. If receptor stimulation results in the postsynaptic membrane becoming more electrically positive (depolarized), it is an excitatory postsynaptic potential (EPSP).

If more negative (hyperpolarized), it is an inhibitory postsynaptic potential (IPSP). Excitation and inhibition depend on the properties of the receptor and not the neurotransmitter. Receptors coupled to sodium or calcium channels are excitatory and produce a depolarization of the postsynaptic membrane, whereas receptors coupled to chloride or potassium channels are inhibitory and produce a hyperpolarization of the postsynaptic membrane.

Such receptors coupled to ion channels are called ionotropic receptors. Other receptors are coupled to ""second-messenger"" systems that initiate a series of biochemical reactions in the postsynaptic cell. These are metabotropic receptors . Metabotropic receptors can produce many different Synapses are junctional complexes between the presynaptic neuron and the postsynaptic neuron.

Presynaptic is the transmitting side of the nerve impulse and postsynaptic is the receiving side. postsynaptic events. These range from the direct activation of adjacent ion channels, to alteration of receptor sensitivity, to transcription of specific messenger ribonucleic acids (RNAs), or even the activation of specific genes .

Chemical synapses are part of a very adaptable and flexible communications system. These are not static anatomical structures with fixed properties but are dynamic structures, able to change their molecular properties with changing circumstances.

There are literally hundreds of neurotransmitters. Some are fairly simple compounds such as acetylcholine, serotonin, the catecholamines (dopamine, norepinephrine, and epinephrine) and a number of the amino acids . Many are more complex and belong to the vast array of neuropeptide transmitters. Once released into the synaptic cleft, neurotransmitters remain active until they are either altered chemically or taken back into the synaptic knob by special carrier systems and recycled.

At cholinergic synapses, acetylcholinesterase is present in the synaptic cleft. This enzyme cleaves the neurotransmitter into acetate and choline, neither of which is active. Serotonin and epinephrine, on the other hand, are taken up into the presynaptic terminal and recycled. Electrical Synapses Electrical synapses, although rare in vertebrate nervous systems, do exist. In an electrical synapse, or gap junction, the presynaptic and postsynaptic membranes are partially fused.

This allows the action potential to cross from the membrane of one neuron to the next without the intervention of a neurotransmitter. Electrical synapses often lack the directional specificity of chemical synapses and may transmit a signal in either direction. During biological activity, electrical synapses do not have the potential for as much variation as do chemical synapses.

SEE ALSO Amino Acid ; Exocytosis ; Hormones ; Ion Channels ; Muscle Alvin M. Burt Bibliography Burt, Alvin M. ""Histology and Fine Structure of Nervous Tissue,"" ""Neuronal Communication,"" and ""Chemical Transmission.""

In Textbook of Neuroanatomy. Philadelphia, PA: W. B. Saunders, Co., 1993. Saladin, Kenneth S. ""Nervous Tissue."" In Anatomy and Physiology: The Unity of Form and Function. New York: Mc Graw-Hill, 2001. LOEWI, OTTO (1873–1961)German-born American physician who received, with Henry Dale, the 1936 Nobel Prize in physiology for the discovery of a substance that stimulates nerve cells. In the 1920s, Loewi provided the first evidence that chemicals transmit impulses between nerves and organs, such as the heart. "

ma. Its receptor is linked to a G protein. d. Acetylcholine is released by axon terminals of the motor neuron.d. Acetylcholine is released by axon terminals of the motor neuron. Action potentials travel the length of the axons of motor neurons to the axon terminals.

Map #7

Study your flashcards anywhere!Download the official Cram app for free >How to study your flashcards.

Right/Left arrow keys: Navigate between flashcards. right arrow key left arrow key Up/Down arrow keys: Flip the card between the front and back.

down key up key H key: Show hint (3rd side). h key A key: Read text to speech. a key Click or Press Spacebar to Begin »Card Range To Studythrough Share Print Export Clone57 Cards in this Set Front Back Action potential propagation in a skeletal muscle fiber ceases when acetylcholine is removed from the synaptic cleft. Which of the following mechanisms ensures a rapid and efficient removal of acetylcholine? a. Acetylcholine is transported back into the axon terminal by a reuptake mechanism. b. Acetylcholine is transported into the postsynaptic neuron by receptor-mediated endocytosis. c. Acetylcholine diffuses away from the cleft.

d. Acetylcholine is degraded by acetylcholinesterase.d. Acetylcholine is degraded by acetylcholinesterase. The neuromuscular junction is a well-studied example of a chemical synapse. Which of the following statements describes a critical event that occurs at the neuromuscular junction?

a. Acetylcholine is released and moves across the synaptic cleft bound to a transport protein. b. When the action potential reaches the end of the axon terminal, voltage-gated sodium channels open and sodium ions diffuse into the terminal. c. Acetylcholine binds to its receptor in the junctional folds of the sarcolem

These motor neurons __________.extend from the brain or spinal cord to the sarcolemma of a skeletal muscle fiber Calcium entry into the axon terminal triggers what events?

Synaptic vesicles fuse to the plasma membrane of the axon terminal and release acetylcholine. Acetylcholine binds to its receptor in the sarcolemma and triggers __________.the opening of ligand-gated cation channels Sodium and potassium ions do not diffuse in equal numbers through ligand-gated cation channels.

Why? The inside surface of the sarcolemma is negatively charged compared to the outside surface. Sodium ions diffuse inward along favorable chemical and electrical gradients. Excitation-contraction coupling is a series of events that occur after the events of the neuromuscular junction have transpired. The term excitation refers to which step in the process? Excitation, in this case, refers to the propagation of action potentials along the sarcolemma.

Excitation of the sarcolemma is coupled or linked to the contraction of a skeletal muscle fiber. What specific event initiates the contraction? Calcium release from the sarcoplasmic reticulum initiates the contraction. A triad is composed of a T-tubule and two adjacent terminal cisternae of the sarcoplasmic reticulum.

How are these components connected? A series of proteins that control calcium release. What is name given to the regularly spaced infoldings of the sarcolemma?transverse or T tubules Page of 6|Showing cards per page Previous | Next