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Neuron: neuron (Nerve Cell)
.(A) Denotes Purkinje cells, an example of a multipolar neuron.^ For example, as one examines mature motor neurons of progressively larger size, cell body area increases faster than nuclear area in each of these animals. Normal Motor Neurons 6 February 2010 12:41 UTC www.med.unc.edu [Source type: Academic] ^ From the beginning, for example, we wanted to know the total protein content of the isolated motor neuron cell bodies we studied. Normal Motor Neurons 6 February 2010 12:41 UTC www.med.unc.edu [Source type: Academic] ^ Neurons with long, but thin axons ( e.g ., c fibers), or large cell bodies and short axons (Purkinje cells) are excluded from this definition. Normal Motor Neurons 6 February 2010 12:41 UTC www.med.unc.edu [Source type: Academic] (B) Denotes granule cells which are also multipolar." src="http://images-mediawiki-sites.thefullwiki.org/00/2/5/3/99975441042417957.jpg" width="240" height="281" /> .Drawing by Santiago Ramón y Cajal of neurons in the pigeon cerebellum.^ Neuron preparation by Ramón y Cajal . Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic] .(A) Denotes Purkinje cells, an example of a multipolar neuron.^ For example, as one examines mature motor neurons of progressively larger size, cell body area increases faster than nuclear area in each of these animals. Normal Motor Neurons 6 February 2010 12:41 UTC www.med.unc.edu [Source type: Academic] ^ From the beginning, for example, we wanted to know the total protein content of the isolated motor neuron cell bodies we studied. Normal Motor Neurons 6 February 2010 12:41 UTC www.med.unc.edu [Source type: Academic] ^ Neurons with long, but thin axons ( e.g ., c fibers), or large cell bodies and short axons (Purkinje cells) are excluded from this definition. Normal Motor Neurons 6 February 2010 12:41 UTC www.med.unc.edu [Source type: Academic] (B) Denotes granule cells which are also multipolar.
NeuroLex ID	sao1417703748

Neuroscience portal

Overview

Structure of a typical neuron

Neuron

.A thick axon trails away from the mass, ending with further branching which are labeled as axon terminals.^ 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. Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic] ^ The terminal branches of an axon make synaptic contacts onto other nerve cells (or with peripheral effectors, i.e. Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic] ^ Make sure the person holding the synaptic terminal keeps his or her hands AWAY from the place the axon attaches (more about this later). Neuroscience for Kids - Models 9 January 2010 15:13 UTC faculty.washington.edu [Source type: FILTERED WITH BAYES] .Along the axon are a number of protuberances labeled as myelin sheaths."^ Some axons are wrapped in a myelin sheath formed from the plasma membranes of specialized glial cells known as Schwann cells . the nervous system 6 February 2010 12:41 UTC www.emc.maricopa.edu [Source type: Academic] ^ This neuron pipe cleaners of 5 different colors: one color each for the dendrites, cell body, axon, myelin sheath and synaptic terminal. Neuroscience for Kids - Models 9 January 2010 15:13 UTC faculty.washington.edu [Source type: FILTERED WITH BAYES] ^ The axons and dendrites are surrounded by a white myelin sheath. the nervous system 6 February 2010 12:41 UTC www.emc.maricopa.edu [Source type: Academic] src="http://images-mediawiki-sites.thefullwiki.org/01/1/9/1/58020532121475006.png" width="400" height="215" /> Dendrite Soma Axon Nucleus Node of Ranvier Axon terminal Schwann cell Myelin sheath

Anatomy and histology

Diagram of a typical myelinated vertebrate motoneuron.

• The soma is the central part of the neuron. .It contains the nucleus of the cell, and therefore is where most protein synthesis occurs.^ Cell Body - contains nucleus and organelles .
  • Neurons 6 February 2010 12:41 UTC faculty.clintoncc.suny.edu [Source type: Academic]
  
  ^ The DNA is located here, in the nucleus , and most of the protein synthesis in the cell occurs here.
  • neuron@Everything2.com 9 January 2010 15:13 UTC www.everything2.com [Source type: FILTERED WITH BAYES]
  
  ^ It contains the nucleus of the cell, and therefore is where most protein synthesis occurs.
  • Neurons - Psychology Wiki 6 February 2010 12:41 UTC psychology.wikia.com [Source type: Academic]
  
  .The nucleus ranges from 3 to 18 micrometers in diameter.^ The nucleus ranges from 3 to 18 micrometers in diameter.
  • Neurons - Psychology Wiki 6 February 2010 12:41 UTC psychology.wikia.com [Source type: Academic]
  
  ^ Axon and dendrites alike are typically only about a micrometer thick, while the soma is usually about 25 micrometers in diameter and not much larger than than the cell nucleus it contains.
  • Neuron 9 January 2010 15:13 UTC www.websters-online-dictionary.org [Source type: Reference]
  
  ^ The soma is usually about 10–25 micrometers in diameter and often is not much larger than the cell nucleus it contains.
  • Neurons - Psychology Wiki 6 February 2010 12:41 UTC psychology.wikia.com [Source type: Academic]
  
  ^[2]
.

• The dendrites of a neuron are cellular extensions with many branches, and metaphorically this overall shape and structure is referred to as a dendritic tree.^ It is a popular product for creating 3D morphological reconstructions of neurons with complex dendritic trees (although this is not the only functionality).
  • Glossary of the main terms used in neuroConstruct 9 January 2010 15:13 UTC www.neuroconstruct.org [Source type: Reference]
  
  ^ 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.
  • Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]
  
  ^ Stellate cells are intrinsic neurons named for their star-like shape, which results from dendrites arising in many directions.
  • Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]
  
  .This is where the majority of input to the neuron occurs.

• The axon is a finer, cable-like projection which can extend tens, hundreds, or even tens of thousands of times the diameter of the soma in length.^ The largest nerve cells in this preparation represent spinal motor neurons , the cells whose very long axons extend out peripheral nerves to the muscles.
  • Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]
  
  ^ This matrix extends into the proximal dendrites of the motor neuron and we strongly suspect that it will be found throughout most of the extent of both the dendrites and axon.
  • Normal Motor Neurons 6 February 2010 12:41 UTC www.med.unc.edu [Source type: Academic]
  
  ^ A three-dimensional network of at least one hundred neurons is needed to create a meaningful thought, although typically more than a thousand neurons are involved.
  • The Theory of Consciousness 9 January 2010 15:13 UTC neuron4.net [Source type: FILTERED WITH BAYES]
  
  .The axon carries nerve signals away from the soma (and also carries some types of information back to it).^ A neuron or nerve cell consists of a cell body (soma), which contains the nucleus, dendrites, an axon and its terminals.
  • The Theory of Consciousness 9 January 2010 15:13 UTC neuron4.net [Source type: FILTERED WITH BAYES]
  
  ^ Your hand represents the "cell body" (also called the "soma"); your fingers represent "dendrites" bringing information to the cell body; your arm represents the "axon" taking information away from the cell body.
  • Neuroscience for Kids - Models 9 January 2010 15:13 UTC faculty.washington.edu [Source type: FILTERED WITH BAYES]
  
  .Many neurons have only one axon, but this axon may—and usually will—undergo extensive branching, enabling communication with many target cells.^ Each nerve cell has one and only one axon.
  • Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]
  
  ^ The upshot of these two laborious projects was that one-half to two-thirds of new protein from motor neuron cell bodies may be exported within 4 hours.
  • Normal Motor Neurons 6 February 2010 12:41 UTC www.med.unc.edu [Source type: Academic]
  
  ^ The small fraction of total new protein that is rapidly transported into the axon may be related to the 10% of total labeled protein that remains in motor neuron cell bodies that are isolated from frozen, non-cryoprotected tissue .
  • Normal Motor Neurons 6 February 2010 12:41 UTC www.med.unc.edu [Source type: Academic]
  
  .The part of the axon where it emerges from the soma is called the axon hillock.^ Axonal nerve signals, called action potentials are initiated at the axon hillock, the site where an axon arises from the cell body.
  • Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]
  
  ^ Your hand represents the "cell body" (also called the "soma"); your fingers represent "dendrites" bringing information to the cell body; your arm represents the "axon" taking information away from the cell body.
  • Neuroscience for Kids - Models 9 January 2010 15:13 UTC faculty.washington.edu [Source type: FILTERED WITH BAYES]
  
  .Besides being an anatomical structure, the axon hillock is also the part of the neuron that has the greatest density of voltage-dependent sodium channels.^ 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.
  • Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]
  
  ^ 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).
  • Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]
  
  .This makes it the most easily-excited part of the neuron and the spike initiation zone for the axon: in neurological terms it has the most negative action potential threshold.^ This simulates the depolarization of the neuron above its threshold value and the generation of an action potential.
  • Neuroscience for Kids - Models 9 January 2010 15:13 UTC faculty.washington.edu [Source type: FILTERED WITH BAYES]
  
  ^ If the electrical potential is raised so that it reaches the threshold, an action potential will fire down the axon of a neuron.
  • Neuroscience for Kids - Models 9 January 2010 15:13 UTC faculty.washington.edu [Source type: FILTERED WITH BAYES]
  
  ^ Grades 3-12 Saltatory conduction is a way that myelinated axons transmit action potentials.
  • Neuroscience for Kids - Models 9 January 2010 15:13 UTC faculty.washington.edu [Source type: FILTERED WITH BAYES]
  
  While the axon and axon hillock are generally involved in information outflow, this region can also receive input from other neurons.

• The axon terminal contains synapses, specialized structures where neurotransmitter chemicals are released in order to communicate with target neurons.

Histology and internal structure

Golgi-stained neurons in human hippocampal tissue.

Classes

.

Image of pyramidal neurons in mouse cerebral cortex expressing green fluorescent protein.^ Information from primary sensory neurons does not reach the highest levels (the cerebral cortex) directly.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ Pyramidal cells are the efferent (long-axon) cells of the cerebral cortex .

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ Upper motor neurons , pyramidal cells located in the motor cortex , relay information to the lower motor neurons.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

.The red staining indicates GABAergic interneurons.^ The red staining indicates GABAergic interneurons.

• Neurons - Psychology Wiki 6 February 2010 12:41 UTC psychology.wikia.com [Source type: Academic]

Source PLoS Biology [1]

SMI32-stained pyramidal neurons in cerebral cortex.

Structural classification

Polarity

• Unipolar or pseudounipolar: dendrite and axon emerging from same process.
• Bipolar: axon and single dendrite on opposite ends of the soma.
• Multipolar: more than two dendrites:
  • Golgi I: neurons with long-projecting axonal processes; examples are pyramidal cells, Purkinje cells, and anterior horn cells.
  • Golgi II: neurons whose axonal process projects locally; the best example is the granule cell.

Other

• Basket cells, neurons with dilated and knotty dendrites in the cerebellum.
• Betz cells, large motor neurons.
• Medium spiny neurons, most neurons in the corpus striatum.
• Purkinje cells, huge neurons in the cerebellum, a type of Golgi I multipolar neuron.
• Pyramidal cells, neurons with triangular soma, a type of Golgi I.
• Renshaw cells, neurons with both ends linked to alpha motor neurons.
• Granule cells, a type of Golgi II neuron.
• anterior horn cells, motoneurons located in the spinal cord.

Functional classification

Direction

• Afferent neurons convey information from tissues and organs into the central nervous system and are sometimes also called sensory neurons.
• Efferent neurons transmit signals from the central nervous system to the effector cells and are sometimes called motor neurons.
• Interneurons connect neurons within specific regions of the central nervous system.

Action on other neurons

Discharge patterns

• Tonic or regular spiking.^ Tonic or regular spiking .
  • Neurons - Psychology Wiki 6 February 2010 12:41 UTC psychology.wikia.com [Source type: Academic]
  
  .Some neurons are typically constantly (or tonically) active.^ Some neurons are typically constantly (or tonically) active.
  • Neurons - Psychology Wiki 6 February 2010 12:41 UTC psychology.wikia.com [Source type: Academic]
  
  ^ Thus, rather than functioning as individual units, in some parts of the brain large ensembles of neurons may be active simultaneously to process neural information.
  • Neurons - Psychology Wiki 6 February 2010 12:41 UTC psychology.wikia.com [Source type: Academic]
  
  ^ Below is a table listing these ions and some important information about them for typical mammalian neurons.
  • neuron@Everything2.com 9 January 2010 15:13 UTC www.everything2.com [Source type: FILTERED WITH BAYES]
  
  .Example: interneurons in neurostriatum.
• Phasic or bursting.^ Example: interneurons in neurostriatum.
  • Neurons - Psychology Wiki 6 February 2010 12:41 UTC psychology.wikia.com [Source type: Academic]
  
  .Neurons that fire in bursts are called phasic.
• Fast spiking.^ Neurons that fire in bursts are called phasic.
  • Neurons - Psychology Wiki 6 February 2010 12:41 UTC psychology.wikia.com [Source type: Academic]
  
  ^ Some neurons are notable for their fast firing rates, for example some types of cortical inhibitory interneurons, cells in globus pallidus.
  • Neurons - Psychology Wiki 6 February 2010 12:41 UTC psychology.wikia.com [Source type: Academic]
  
  ^ When a neuron fires a signal, it actually sends chemicals called neurotransmitters over the gap, or synapse , that separates the brain cells from one another.
  • MSMR: What A Year! Introducing Medical Discoveries to Biology Students - 3/08: Batten Disease 9 January 2010 15:13 UTC www.whatayear.org [Source type: Academic]
  
  .Some neurons are notable for their fast firing rates, for example some types of cortical inhibitory interneurons, cells in globus pallidus, retinal ganglion cells.^ These size relationships are not isometric, but are allometric, with some degree of independence in nuclear and cell body size over the range of motor neuron sizes.
  • Normal Motor Neurons 6 February 2010 12:41 UTC www.med.unc.edu [Source type: Academic]
  
  ^ In general, we found that isolated motor neuron cell bodies are notably rigid structures.
  • Normal Motor Neurons 6 February 2010 12:41 UTC www.med.unc.edu [Source type: Academic]
  
  ^ These pyramidal cells comprise some of the upper motor neurons.
  • Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]
  
  ^[6][7]
• Thin-spike. .Action potentials of some neurons are more narrow compared to the others.^ Then, the neuron fires an action potential.
  • Physics Buzz: Making Neurons Remember 6 February 2010 12:41 UTC physicsbuzz.physicscentral.com [Source type: FILTERED WITH BAYES]
  
  ^ Classification by action on other neurons .
  • Neurons - Psychology Wiki 6 February 2010 12:41 UTC psychology.wikia.com [Source type: Academic]
  
  ^ Action potentials of some neurons are more narrow compared to the others.
  • Neurons - Psychology Wiki 6 February 2010 12:41 UTC psychology.wikia.com [Source type: Academic]
  
  For example, interneurons in the prefrontal cortex are thin-spike neurons.

Classification by neurotransmitter production

.Neurons differ in the type of neurotransmitter they manufacture.^ 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.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ We found many differences in the soluble proteins in isolated motor neuron cell bodies and the ventral gray matter from which they were obtained ( Weil and McIlwain, 1981 ).

• Normal Motor Neurons 6 February 2010 12:41 UTC www.med.unc.edu [Source type: Academic]

^ Neurohistology is burdened by a profusion of names for different neuronal cell types.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

Some examples are

• cholinergic neurons - acetylcholine

.Acetylcholine is released from presynaptic neurons into the synaptic cleft.^ 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."

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

It acts as a ligand for Nicotinic Acetylcholine receptors, which are ligand gated Na+ ion channels. Ligand binding opens the channel causing depolarization and increases the probability of an action potential firing, occcuring once the threshold is reached.

• GABAergic neurons - gamma aminobutyric acid

.GABA is one of two neuroinhibitors in the CNS, the other being Glycine.^ Their axons arise in one region of the CNS where the cell body resides and end somewhere else (sometimes several other places).

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

GABA has a homologous function to ACh, gating anion channels that allow Cl- ions to enter the post synaptic neuron. Cl- causes hyperpolarization within the neuron, decreasing the probability of an action potential firing as the voltage becomes more negative (recall that for an action potential to fire, a positive voltage threshold must be reached).

• glutamatergic neurons - glutamate

Glutamate is one of two primary neuroexcitors, the other being Aspartate (not Aspartame). Glutamate receptors are one of four categories, three of which are ion channels and one of which is a G-protein coupled receptor (often referred to as GPCR). .1 - AMPA and Kainate receptors (really two different receptors) both function as Na⁺ cation channels mediating fast excitatory synaptic transmission 2 - NMDA receptors are another cation channel, but for Ca²⁺.^ The two principal types of glia, oligodendroglia and astroglia , both have extensive cytoplasmic processes and are intimately involved in the function of nervous tissue.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

The function of NMDA receptors is dependant on Glycine binding to a mediator binding spot on the channel pore. NMDA receptors will not function without both ligands present - antagonist drugs for Glycine will cause NMDA receptors to malfunction. .3 - Metabotropic receptor, a GPCR that modulates synaptic transmission Glutamate can cause excitotoxicity when blood flow to the brain is interrupted, resulting in brain damage.^ 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.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

.When blood flow is suppressed, glutamate is released from presynaptic neurons causing NMDA and AMPA receptor activation moreso than would normally be the case outside of stress conditions, leading to elevated Ca²⁺ and Na⁺ entering the post synaptic neuron and cell damage.^ In a post-synaptic neuron the terminology is actually EPSP. When you're getting into this specific of terminology about the potentials, AP is too vague I feel.

• MEPP, EPP and acetylcholine help | Allopathic | Student Doctor Network 9 January 2010 15:13 UTC forums.studentdoctor.net [Source type: General]

^ 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.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ Originally Posted by illixir EPSP stands for excitatory post synaptic potential, implying a post synaptic neuron , definately not at the neuromuscular junction.

• MEPP, EPP and acetylcholine help | Allopathic | Student Doctor Network 9 January 2010 15:13 UTC forums.studentdoctor.net [Source type: General]

• dopaminergic neurons - dopamine

.Dopamine is a neurotransmitter that acts on a GPCR. Dopamine is connected to mood and behaviour, and modulates post synaptic neurotransmission.^ 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.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

Loss of dopamine neurons has been linked to Parkinson's disease, schizophrenia, and ADD.

• serotonergic neurons - serotonin

Serotonin, full name 5-Hydroxytriptamine, can act as excitatory or inhibitory. Of the four 5HT receptor classes, 3 are GPCR and 1 is ligand gated cation channel. Serotonin is synthesized from tryptophan by tryptophan hydroxylase, and then further by aromatic acid decarboxylase. A lack of 5HT at postsynaptic neurons has been linked to depression. Drugs that are antagonistic for reabsorption by presynaptic neurons are used for treatment, such as Prozac and Zoloft.

Connectivity

Main article: Synapse

.Neurons communicate with one another via synapses, where the axon terminal or en passant boutons (terminals located along the length of the axon) of one cell impinges upon another neuron's dendrite, soma or, less commonly, axon.^ Each nerve cell has one and only one axon.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ Synapses are points of contact between nerve cells (usually between axon terminals and dendrites), where signals are transmitted from one cell to another.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ 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 ."

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

.Neurons such as Purkinje cells in the cerebellum can have over 1000 dendritic branches, making connections with tens of thousands of other cells; other neurons, such as the magnocellular neurons of the supraoptic nucleus, have only one or two dendrites, each of which receives thousands of synapses.^ Each nerve cell has one and only one axon.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ 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.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ 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.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

.Synapses can be excitatory or inhibitory and will either increase or decrease activity in the target neuron.^ Stimulating excitatory neurons will increase network activity while stimulating inhibitory neurons reduces it.

• Physics Buzz: Making Neurons Remember 6 February 2010 12:41 UTC physicsbuzz.physicscentral.com [Source type: FILTERED WITH BAYES]

^ Inhibitory neurons inhibit their target neurons.

• Neurons - Psychology Wiki 6 February 2010 12:41 UTC psychology.wikia.com [Source type: Academic]

^ Excitatory neurons excite their target neurons.

• Neurons - Psychology Wiki 6 February 2010 12:41 UTC psychology.wikia.com [Source type: Academic]

.Some neurons also communicate via electrical synapses, which are direct, electrically-conductive junctions between cells.^ A synapse is a junction between a neuron and another cell.

• Neurons 6 February 2010 12:41 UTC faculty.clintoncc.suny.edu [Source type: Academic]

^ Neurons communicate via chemical and electrical synapses , in a process known as synaptic transmission .

• Neurons - Psychology Wiki 6 February 2010 12:41 UTC psychology.wikia.com [Source type: Academic]

^ Electrical Synapse Current determined by a conductance and the voltage difference between two cells.

• Neuron Models 9 January 2010 15:13 UTC instruct1.cit.cornell.edu [Source type: Academic]

.In a chemical synapse, the process of synaptic transmission is as follows: when an action potential reaches the axon terminal, it opens voltage-gated calcium channels, allowing calcium ions to enter the terminal.^ The axon terminal is then the presynaptic terminal of a synapse.

• Neurons 6 February 2010 12:41 UTC faculty.stcc.edu [Source type: FILTERED WITH BAYES]

^ Each synapse has a pre synaptic side -- an axon terminal -- from which a neurotransmitter is released.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ Once the slowly-opening voltage-gated potassium ion-channels have opened and allowed potassium to flow out, the action potential is ended.

• BASIC NEURON PHYSIOLOGY 9 January 2010 15:13 UTC www.benbest.com [Source type: Academic]

.Calcium causes synaptic vesicles filled with neurotransmitter molecules to fuse with the membrane, releasing their contents into the synaptic cleft.^ Each synapse has a pre synaptic side -- an axon terminal -- from which a neurotransmitter is released.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ Neurotransmitter is released in response to changes in membrane potential associated with arrival of action potentials.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ Neurotransmitter is usually stored in synaptic vesicles within the presynaptic terminal.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

.The neurotransmitters diffuse across the synaptic cleft and activate receptors on the postsynaptic neuron.^ The neurotransmitter molecules diffuse across the synaptic cleft, bind briefly to receptors on the postsynaptic neuron to activate them, causing physiological responses that may be excitatory or inhibitory depending on the receptor.

• Human Physiology - Neurons & the Nervous System 6 February 2010 12:41 UTC people.eku.edu [Source type: Academic]

^ The neurotransmitter molecules diffuse across the cleft and fit into receptor sites in the postsynaptic membrane.

• Human Physiology - Neurons & the Nervous System 6 February 2010 12:41 UTC people.eku.edu [Source type: Academic]

^ If the initial state of the synaptic connections was strong where the amount of chemical neurotransmitter released was reliable, the plasticity response was largely controlled by the receiver neuron and was weakened in response to bouts of nearly coincident sender-receiver activation.

• Baylor studies learning, memory > Waller County News Citizen > Lifestyles Archives > Houston Community Newspapers Online - News Around Town 9 January 2010 15:13 UTC www.hcnonline.com [Source type: FILTERED WITH BAYES]

.The human brain has a huge number of synapses.^ The human brain has a huge number of synapses.

• Neurons - Psychology Wiki 6 February 2010 12:41 UTC psychology.wikia.com [Source type: Academic]

^ There are about 100 billion neurons within the human central nervous system (brain and spinal cord) with an estimated 100 trillion synapses (connections between neurons).

• Neurons - Tag | Brain Blogger 6 February 2010 12:41 UTC brainblogger.com [Source type: FILTERED WITH BAYES]

^ The human brain also contains a number of hard-wired features.

• The Theory of Consciousness 9 January 2010 15:13 UTC neuron4.net [Source type: FILTERED WITH BAYES]

.Each of the 10¹¹ (one hundred billion) neurons has on average 7,000 synaptic connections to other neurons.^ 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 ."

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ 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.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ 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.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

.It has been estimated that the brain of a three-year-old child has about 10¹⁵ synapses (1 quadrillion).^ Microglia are small cells, comprising about 10% of the total brain cell populaton, which are believed to represent the brain's immune system (i.e., macrophage-equivalents residing within the brain).

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

.This number declines with age, stabilizing by adulthood.^ This number declines with age, stabilizing by adulthood.

• Neurons - Psychology Wiki 6 February 2010 12:41 UTC psychology.wikia.com [Source type: Academic]

Estimates vary for an adult, ranging from 10¹⁴ to 5 x 10¹⁴ synapses (100 to 500 trillion).^[8]

Mechanisms for propagating action potentials

A signal propagating down an axon to the cell body and dendrites of the next cell.

In 1937, John Zachary Young suggested that the squid giant axon could be used to study neuronal electrical properties.^[9] .Being larger than but similar in nature to human neurons, squid cells were easier to study.^ Schwann cell nuclei are usually larger and with less-condensed chromatin than fibroblast nuclei.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ 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.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ 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 .

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

.By inserting electrodes into the giant squid axons, accurate measurements were made of the membrane potential.^ Observe that as the growing Schwann cell spirals inward around the axon, it wraps its membrane into layers of myelin.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

.The cell membrane of the axon and soma contain voltage-gated ion channels which allow the neuron to generate and propagate an electrical signal (an action potential).^ Action potentials are active, all-or-nothing signals which do not decline in strength as they travel along the axon..

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ Cell bodies of short-axon neurons are often small and numerous.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ Axonal nerve signals, called action potentials are initiated at the axon hillock, the site where an axon arises from the cell body.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

.These signals are generated and propagated by charge-carrying ions including sodium (Na⁺), potassium (K⁺), chloride (Cl^-), and calcium (Ca²⁺).^ 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.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

.There are several stimuli that can activate a neuron leading to electrical activity, including pressure, stretch, chemical transmitters, and changes of the electric potential across the cell membrane.^ Neurotransmitter is released in response to changes in membrane potential associated with arrival of action potentials.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^[10] .Stimuli cause specific ion-channels within the cell membrane to open, leading to a flow of ions through the cell membrane, changing the membrane potential.^ Neurotransmitter is released in response to changes in membrane potential associated with arrival of action potentials.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ 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.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

.Thin neurons and axons require less metabolic expense to produce and carry action potentials, but thicker axons convey impulses more rapidly.^ In some white matter areas most axons are travelling in parallel, with all action potentials propagating in the same direction.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ Action potentials are active, all-or-nothing signals which do not decline in strength as they travel along the axon..

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ Axonal nerve signals, called action potentials are initiated at the axon hillock, the site where an axon arises from the cell body.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

.To minimize metabolic expense while maintaining rapid conduction, many neurons have insulating sheaths of myelin around their axons.^ In peripheral nerve cross sections stained for myelin, the myelin is generally visible as a dark or black frame around each pale myelinated axon.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ Each oligodendroglial cell has several such "shovels", forming myelin around several axons.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ Myelin formation by oligodendroglia is slightly different than that by Schwann cells , each of which wraps myelin around a single axon.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

.The sheaths are formed by glial cells: oligodendrocytes in the central nervous system and Schwann cells in the peripheral nervous system.^ Glial cells -- Support cells of the CENTRAL NERVOUS SYSTEM .

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ Nearly all the nerve cells in the central nervous system are interneurons.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ The most numerous cells within the central nervous system are glial cells .

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

.The sheath enables action potentials to travel faster than in unmyelinated axons of the same diameter, whilst using less energy.^ Unmyelinated axons are usually quite small, less than 1µm in diameter.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ The sheath enables action potentials to travel faster than in unmyelinated axons of the same diameter, whilst using less energy.

• Neurons - Psychology Wiki 6 February 2010 12:41 UTC psychology.wikia.com [Source type: Academic]

^ The size of the action potential stays the same as it travels down the axon.

• Neuroscience for Kids - Models 9 January 2010 15:13 UTC faculty.washington.edu [Source type: FILTERED WITH BAYES]

.The myelin sheath in peripheral nerves normally runs along the axon in sections about 1 mm long, punctuated by unsheathed nodes of Ranvier which contain a high density of voltage-gated ion channels.^ White matter has voltage gated ion channels, whereas grey matter (not myelinated) has neurotransmitter gated ion channels.

• Neurons - un knol de Kevin Spaulding 6 February 2010 12:41 UTC knol.google.com [Source type: Academic]

^ The myelin sheath in peripheral nerves normally runs along the axon in sections about 1 mm long, punctuated by unsheathed nodes of Ranvier which contain a high density of voltage-gated ion channels.

• Neurons - Psychology Wiki 6 February 2010 12:41 UTC psychology.wikia.com [Source type: Academic]

^ A layer of fatty cells, the myelin sheath punctuated by the unsheathed nodes of Ranvier, insulates the axons of some neurons and speeds the impulses.

• The inner workings of the brain. 9 January 2010 15:13 UTC www.thebigview.com [Source type: Academic]

.Multiple sclerosis is a neurological disorder that results from demyelination of axons in the central nervous system.^ The central nervous system is enveloped by specialized layers of connective tissue.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ The most numerous cells within the central nervous system are glial cells .

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ Patchy loss of CNS myelin, as in multiple sclerosis ( WebPath , WebPath w/ MRI ), can cause a variety of neurological problems.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

.Some neurons do not generate action potentials, but instead generate a graded electrical signal, which in turn causes graded neurotransmitter release.^ Then, the neuron fires an action potential.

• Physics Buzz: Making Neurons Remember 6 February 2010 12:41 UTC physicsbuzz.physicscentral.com [Source type: FILTERED WITH BAYES]

^ Numerically, the dominant class of neurons in an animal do not generate action potentials .

• THE STANDARDIZED NEURON portion of PROCESSES IN BIOLOGICAL VISION 9 January 2010 15:13 UTC neuronresearch.net [Source type: Academic]

^ Neurons communicate with one another using electrical signals, or potentials.

• Neurons - un knol de Kevin Spaulding 6 February 2010 12:41 UTC knol.google.com [Source type: Academic]

.Such nonspiking neurons tend to be sensory neurons or interneurons, because they cannot carry signals long distances.^ Such nonspiking neurons tend to be sensory neurons or interneurons, because they cannot carry signals long distances.

• Neurons - Psychology Wiki 6 February 2010 12:41 UTC psychology.wikia.com [Source type: Academic]

^ Depending on the number of pulses generated, they initiate or inhibit the 'firing' of new signals along the connecting neuron.

• http://www.holisticeducator.com/neuron.htm 9 January 2010 15:13 UTC www.holisticeducator.com [Source type: Academic]

^ 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.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

All-or-none principle

The conduction of nerve impulses is an example of an all-or-none response. .In other words, if a neuron responds at all, then it must respond completely.^ All other neurons are interneurons .

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

The greater the intensity of stimulation does not produce a stronger signal but can produce more impulses per second. There are different types of receptor response to stimulus, slowly adapting or tonic receptors respond to steady stimulus and produce a steady rate of firing. .These tonic receptors most often respond to increased intensity of stimulus by increasing their firing frequency, usually as a power function of stimulus plotted against impulses per second.^ Most histology textbooks begin with relatively insignificant, and often misleading, details rather than emphasizing features important for understanding nervous tissue function.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

This can be likened to an intrinsic property of light where to get greater intensity of a specific frequency (color) there have to be more photons, as the photons can't become "stronger" for a specific frequency.

There are a number of other receptor types that are called quickly-adapting or phasic receptors, where firing decreases or stops with steady stimulus; examples include: skin when touched by an object causes the neurons to fire, but if the object maintains even pressure against the skin, the neurons stop firing. .The neurons of the skin and muscles that are responsive to pressure and vibration have filtering accessory structures that aid their function.^ 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.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

.The pacinian corpuscle is one such structure; it has concentric layers like an onion which form around the axon terminal.^ Each oligodendroglial cell has several such "shovels", forming myelin around several axons.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ 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.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ Layer IV (the "inner granular layer") contains axonal ramifications of afferent fibers, such as sensory axons from the thalamus.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

When pressure is applied and the corpuscle is deformed, mechanical stimulus is transferred to the axon, which fires. .If the pressure is steady, there is no more stimulus; thus, typically these neurons respond with a transient depolarization during the initial deformation and again when the pressure is removed, which causes the corpuscle to change shape again.^ Note, there is no current means of gracefully deleting an ellipse that has been saved during this process.

• 3DMA-Neuron 9 January 2010 15:13 UTC www.ams.sunysb.edu [Source type: Reference]

^ 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).

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ 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.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

.Other types of adaptation are important in extending the function of a number of other neurons.^ 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.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ Other times knowing how far the neurons of each relay extend will be necessary to determine the site or effects of a lesion.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^[11]

History

The term neuron was coined by the German anatomist Heinrich Wilhelm Waldeyer. .The neuron's place as the primary functional unit of the nervous system was first recognized in the early 20th century through the work of the Spanish anatomist Santiago Ramón y Cajal.^ Neuron preparation by Ramón y Cajal .

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ 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 ).

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ Motor neurons (or motoneurons) convey information out from the central nervous system to muscles or glands.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^[12] .Cajal proposed that neurons were discrete cells that communicated with each other via specialized junctions, or spaces, between cells.^ A synapse is a junction between a neuron and another cell.

• Neurons 6 February 2010 12:41 UTC faculty.clintoncc.suny.edu [Source type: Academic]

^ Neurons vs. Other Cells .

• What Is a Neuron? 6 February 2010 12:41 UTC psychology.about.com [Source type: FILTERED WITH BAYES]

^ Cajal proposed that neurons were discrete cells that communicated with each other via specialized junctions, or spaces, between cells.

• Neurons - Psychology Wiki 6 February 2010 12:41 UTC psychology.wikia.com [Source type: Academic]

^[12] .This became known as the neuron doctrine, one of the central tenets of modern neuroscience.^ This became known as the neuron doctrine , one of the central tenets of modern neuroscience.

• Neurons - Psychology Wiki 6 February 2010 12:41 UTC psychology.wikia.com [Source type: Academic]

^ The neuron doctrine is a central tenet of modern neuroscience, but recent studies suggest that this doctrine needs to be revised.

• Neurons - Psychology Wiki 6 February 2010 12:41 UTC psychology.wikia.com [Source type: Academic]

^ Interconnected networks of neurons process information and give rise to perception by communicating with one another via small electrical impulses known as action potentials.

• PhysOrg.com - neurons 6 February 2010 12:41 UTC www.physorg.com [Source type: Academic]

^[12] .To observe the structure of individual neurons, Cajal used a silver staining method developed by his rival, Camillo Golgi.^ Ramon y Cajal, S. The structure and connexions of neurons.

• The discovery of the neuron : Neurophilosophy 6 February 2010 12:41 UTC scienceblogs.com [Source type: FILTERED WITH BAYES]

^ To observe the structure of individual neurons, Cajal used a silver staining method developed by his rival, Camillo Golgi .

• Neurons - Psychology Wiki 6 February 2010 12:41 UTC psychology.wikia.com [Source type: Academic]

^ Golgi ideas about the structure and function of individual neurons were in error.

• THE NEURON DOCTRINE 9 January 2010 15:13 UTC zlab.rutgers.edu [Source type: Academic]

^[12] .The Golgi stain is an extremely useful method for neuroanatomical investigations because, for reasons unknown, it stains a very small percentage of cells in a tissue, so one is able to see the complete micro structure of individual neurons without much overlap from other cells in the densely packed brain.^ Most pyramidal cells project association fibers to other cortical regions and/or to deeper nuclei of the brain.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ 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.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ One reason the old idea, creationism, was rejected long ago was because it did not fit the evidence.

• Is Believing Evolution like believing the World is Flat? - talk.origins | Google Groups 9 January 2010 15:13 UTC groups.google.com [Source type: FILTERED WITH BAYES]

^[13]

The neuron doctrine

.The neuron doctrine is the now fundamental idea that neurons are the basic structural and functional units of the nervous system.^ Motor neurons (or motoneurons) convey information out from the central nervous system to muscles or glands.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ 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.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ Basic cellular organization of the nervous system is described in Chapter 2 .

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

The theory was put forward by Santiago Ramón y Cajal in the late 19th century. .It held that neurons are discrete cells (not connected in a meshwork), acting as metabolically distinct units.^ 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.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

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

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

Later discoveries yielded a few refinements to the simplest form of the doctrine. .For example, glial cells, which are not considered neurons, play an essential role in information processing.^ But every nerve cell also belongs to a unique population with a particular role in the information processing of the brain.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ In addition, the inflammatory mediators released by microglia during an innate immune response strongly influence neurons and their ability to process information."

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ [Barres] argue[s] that until the roles of nonneuronal cells are more fully understood and considered, neurobiology as a whole will progress only slowly.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^[14] .Also, electrical synapses are more common than previously thought,^[15] meaning that there are direct, cytoplasmic connections between neurons.^ 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.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ And that as long as there are > other theories for the origins of species then the idea of common > decent will be just that; Nothing more then an idea.

• Is Believing Evolution like believing the World is Flat? - talk.origins | Google Groups 9 January 2010 15:13 UTC groups.google.com [Source type: FILTERED WITH BAYES]

^ 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.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

.In fact, there are examples of neurons forming even tighter coupling; the squid giant axon arises from the fusion of multiple neurons that retain individual cell bodies and the crayfish giant axon consists of a series of neurons with high conductance septate junctions.^ Cell bodies of short-axon neurons are often small and numerous.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ 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 .

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ Regions consisting of axons gathered into bundles, to the exclusion of cell bodies, are called white matter .

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^{[citation needed]}

.Cajal also postulated the Law of Dynamic Polarization, which states that a neuron receives signals at its dendrites and cell body and transmits them, as action potentials, along the axon in one direction: away from the cell body.^ Cell bodies of short-axon neurons are often small and numerous.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ Nerve signals travel along dendrites toward the cell body.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ Each nerve cell has one and only one axon.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^[16] .The Law of Dynamic Polarization has important exceptions; dendrites can serve as synaptic output sites of neurons^[17] and axons can receive synaptic inputs.^ 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.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ Horizontal cells are intrinsic neurons whose dendrites and local axons tend to be confined within a layer parallel to a surface.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ All gray matter regions of the brain, both cortex and nuclei, are associated with afferent ("input") and efferent ("output") axons.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^{[citation needed]}

Neurons in the brain

.The number of neurons in the brain varies dramatically from species to species.^ The number of neurons in the brain varies dramatically from species to species.

• Neurons - Psychology Wiki 6 February 2010 12:41 UTC psychology.wikia.com [Source type: Academic]

^ The motor deficits in autism can be easily explained because mirror neurons are just special types of premotor neurons, brain cells essential for planning and selecting actions.

• The Mirror Neuron Revolution: Explaining What Makes Humans Social: Scientific American 6 February 2010 12:41 UTC www.scientificamerican.com [Source type: FILTERED WITH BAYES]

^ The first one is the one we started with: mirror neurons are brain cells specialized for actions.

• The Mirror Neuron Revolution: Explaining What Makes Humans Social: Scientific American 6 February 2010 12:41 UTC www.scientificamerican.com [Source type: FILTERED WITH BAYES]

^[18] .One estimate puts the human brain at about 100 billion (10¹¹) neurons and 100 trillion (10¹⁴) synapses.^ Microglia are small cells, comprising about 10% of the total brain cell populaton, which are believed to represent the brain's immune system (i.e., macrophage-equivalents residing within the brain).

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^[18] .Another estimate is 86 billion neurons of which 16.3 are in the cerebral cortex and 69 in the cerebellum.^ There is cerebral cortex covering the surface of cerebrum and cerebellar cortex covering the surface of the cerebellum.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ Gray matter located on the surface of the brain is called cortex (e.g., cortex of the cerebral hemispheres, cortex of the cerebellum).

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ Information from primary sensory neurons does not reach the highest levels (the cerebral cortex) directly.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^[19] .By contrast, the nematode worm Caenorhabditis elegans has just 302 neurons making it an ideal experimental subject as scientists have been able to map all of the organism's neurons.^ You just have to make sense of it all.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

The fruit fly Drosophila melanogaster, a common subject in biology experiments, has around 100,000 neurons and exhibits many complex behaviors. .Many properties of neurons, from the type of neurotransmitters used to ion channel composition, are maintained across species, allowing scientists to study processes occurring in more complex organisms in much simpler experimental systems.^ Three types of neurons occur.

• the nervous system 6 February 2010 12:41 UTC www.emc.maricopa.edu [Source type: Academic]

^ Many properties of neurons, from the type of neurotransmitters used to ion channel composition, are maintained across species, allowing scientists to study processes occurring in more complex organisms in much simpler experimental systems.

• Neurons - Psychology Wiki 6 February 2010 12:41 UTC psychology.wikia.com [Source type: Academic]

^ The motor deficits in autism can be easily explained because mirror neurons are just special types of premotor neurons, brain cells essential for planning and selecting actions.

• The Mirror Neuron Revolution: Explaining What Makes Humans Social: Scientific American 9 January 2010 15:13 UTC www.sciam.com [Source type: FILTERED WITH BAYES]
• The Mirror Neuron Revolution: Explaining What Makes Humans Social: Scientific American 6 February 2010 12:41 UTC www.scientificamerican.com [Source type: FILTERED WITH BAYES]

Neurological disorders

Main article: Neurology

.Charcot-Marie-Tooth disease (CMT), also known as Hereditary Motor and Sensory Neuropathy (HMSN), Hereditary Sensorimotor Neuropathy (HMSN), or Peroneal Muscular Atrophy, is a heterogeneous inherited disorder of nerves (neuropathy) that is characterized by loss of muscle tissue and touch sensation, predominantly in the feet and legs but also in the hands and arms in the advanced stages of disease.^ Several features may be used to distinguish nerves from smooth muscle or other fibrous tissue .

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ Brain tissue in CJD or Creutzfeldt-Jakob disease ( WebPath , WebPath , WebPath ) is characterized by microscopic vacuoles (hence, "spongiform encephalopathy") and plaques.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ In routine H&E slides, peripheral nerves resemble other fibrous tissues like smooth muscle or collagen .

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

Presently incurable, this disease is one of the most common inherited neurological disorders, with 37 in 100,000 affected.

.Alzheimer's disease (AD), also known simply as Alzheimer's, is a neurodegenerative disease characterized by progressive cognitive deterioration together with declining activities of daily living and neuropsychiatric symptoms or behavioral changes.^ See WebPath for cortical changes associated with Alzheimer's disease .

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ Alzheimer's disease ( WebPath ) is accompanied by cortical changes ( WebPath gross, WebPath , WebPath , WebPath , WebPath , , WebPath , WebPath ) .

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

The most striking early symptom is loss of short-term memory (amnesia), which usually manifests as minor forgetfulness that becomes steadily more pronounced with illness progression, with relative preservation of older memories. As the disorder progresses, cognitive (intellectual) impairment extends to the domains of language (aphasia), skilled movements (apraxia), recognition (agnosia), and functions such as decision-making and planning get impaired.

.Parkinson's disease (also known as Parkinson disease or PD) is a degenerative disorder of the central nervous system that often impairs the sufferer's motor skills and speech.^ WebPath also offers some examples of nervous system pathology, see WebPath CNS Pathology Index and WebPath CNS Degenerative Diseases .

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ Motor neurons (or motoneurons) convey information out from the central nervous system to muscles or glands.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ Glial cells -- Support cells of the CENTRAL NERVOUS SYSTEM .

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

Parkinson's disease belongs to a group of conditions called movement disorders. It is characterized by muscle rigidity, tremor, a slowing of physical movement (bradykinesia), and in extreme cases, a loss of physical movement (akinesia). .The primary symptoms are the results of decreased stimulation of the motor cortex by the basal ganglia, normally caused by the insufficient formation and action of dopamine, which is produced in the dopaminergic neurons of the brain.^ Upper motor neurons , pyramidal cells located in the motor cortex , relay information to the lower motor neurons.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ 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).

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

Secondary symptoms may include high level cognitive dysfunction and subtle language problems. PD is both chronic and progressive.

Myasthenia Gravis is a neuromuscular disease leading to fluctuating muscle weakness and fatigability. Weakness is typically caused by circulating antibodies that block acetylcholine receptors at the post-synaptic neuromuscular junction, inhibiting the stimulative effect of the neurotransmitter acetylcholine. Myasthenia is treated with immunosuppressants, cholinesterase inhibitors and, in selected cases, thymectomy.

Demyelination

Demyelination is the act of demyelinating, or the loss of the myelin sheath insulating the nerves. .When myelin degrades, conduction of signals along the nerve can be impaired or lost, and the nerve eventually withers.^ Nerve signals travel along dendrites toward the cell body.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ The axon is a process which is specialized for conducting signals from one nerve cell to another.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ Axons may be myelinated to increase the speed of signal conduction.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

This leads to certain neurodegenerative disorders like multiple sclerosis, chronic inflammatory demyelinating polyneuropathy.

Axonal degeneration

.Although most injury responses include a calcium influx signaling to promote resealing of severed parts, axonal injuries initially lead to acute axonal degeneration (AAD), which is rapid separation of the proximal and distal ends within 30 minutes of injury.^ Axonal nerve signals, called action potentials are initiated at the axon hillock, the site where an axon arises from the cell body.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

Degeneration follows with swelling of the axolemma, and eventually leads to bead like formation. .Granular disintegration of the axonal cytoskeleton and inner organelles occurs after axolemma degradation.^ Layer IV (the "inner granular layer") contains axonal ramifications of afferent fibers, such as sensory axons from the thalamus.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

Early changes include accumulation of mitochondria in the paranodal regions at the site of injury. Endoplasmic reticulum degrades and mitochondria swell up and eventually disintegrate. The disintegration is dependent on Ubiquitin and Calpain proteases (caused by influx of calcium ion), suggesting that axonal degeneration is an active process. Thus the axon undergoes complete fragmentation. The process takes about roughly 24 hrs in the PNS, and longer in the CNS. The signaling pathways leading to axolemma degeneration are currently unknown.

Nerve regeneration

Main article: Nerve regeneration

.Although neurons do not divide or replicate in most parts of the adult vertebrate brain, it is often possible for axons to regrow if they are severed.^ 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.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ Cell bodies of short-axon neurons are often small and numerous.

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ 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 .

• Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

This can take a long time: after a nerve injury to the human arm, for example, it may take months for feeling to return to the hands and fingers.^{[citation needed]}

References

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4. ^ Alvarez-Buylla A, Garcia-Verdugo JM (February 1, 2002). "Neurogenesis in adult subventricular zone". The Journal of Neuroscience : the Official Journal of the Society for Neuroscience 22 (3): 629–34. PMID 11826091. http://www.jneurosci.org/cgi/pmidlookup?view=long&pmid=11826091. Retrieved 2009-06-20. 
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6. ^ Kolodin, YO; Veselovskaia, NN; Veselovsky, NS; Fedulova, SA. "Ion conductances related to shaping the repetitive firing in rat retinal ganglion cells". Acta Physiologica Congress. http://www.blackwellpublishing.com/aphmeeting/abstract.asp?MeetingID=&id=61198. Retrieved 2009-06-20. 
7. ^ Ionic conductances underlying excitability in tonically firing retinal ganglion cells of adult rat
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11. ^ Eckert, Roger; Randall, David (1983). Animal physiology: mechanisms and adaptations. San Francisco: W.H. Freeman. pp. 239. ISBN 0-7167-1423-x. 
12. ^ ^{a b c d} López-Muñoz, F.; Boya, J., Alamo, C. (16 October 2006). "Neuron theory, the cornerstone of neuroscience, on the centenary of the Nobel Prize award to Santiago Ramón y Cajal". Brain Research Bulletin 70 (4-6): 391–405. doi:10.1016/j.brainresbull.2006.07.010. PMID 17027775. http://www.sciencedirect.com/science/article/B6SYT-4KMYRRC-1/2/b98a884961498c54452886842389ed72. Retrieved 2007-04-02. 
13. ^ Grant, Gunnar; Boya, J; Alamo, C (9 January 2007 (online)). "How the 1906 Nobel Prize in Physiology or Medicine was shared between Golgi and Cajal". Brain Research Reviews 55 (4-6): 490. doi:10.1016/j.brainresrev.2006.11.004. PMID 17027775. http://www.sciencedirect.com/science/article/B6SYS-4MSHXWR-1/2/51f3edfd18b81abbd0a9d56e98de6ceb. Retrieved 2007-04-02. 
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Sources

.

• Kandel E.R., Schwartz, J.H., Jessell, T.M. 2000. Principles of Neural Science, 4th ed., McGraw-Hill, New York.
• Bullock, T.H., Bennett, M.V.L., Johnston, D., Josephson, R., Marder, E., Fields R.D. 2005. The Neuron Doctrine, Redux, Science, V.310, p.^ From Neurons to Neighborhoods: The Science of Early Childhood Development (2000) Institute of Medicine ( IOM ) .
  • From Neurons to Neighborhoods: The Science of Early Childhood Development 6 February 2010 12:41 UTC www.nap.edu [Source type: Academic]
  
  ^ Any thorough neuro text (e.g., Kandel et al., 4th ed., pp.
  • Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]
  
  ^ Text References to Principles of Neural Science , by Kandel, Schwartz and Jessell.
  • Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]
  
   .791-793.
• Ramón y Cajal, S. 1933 Histology, 10th ed., Wood, Baltimore.
• Roberts A., Bush B.M.H. 1981. Neurones Without Impulses.^ As a result of his findings Cajal formulated his ' neuron doctrine ' according to which  he described neurons as independent cells without ' protoplasmic bridges ' connecting them.
  • http://www.holisticeducator.com/neuron.htm 9 January 2010 15:13 UTC www.holisticeducator.com [Source type: Academic]
  
  ^ NEURON IS A TRANDUCER, CONDUCTOR AND TRANSMITTER OF NERVE IMPULSES Cajal recognized that the neuron had the properties of a transducer, a conductor, and a transmitter of electrical impulses ...converting energy from one form to another.
  • http://www.holisticeducator.com/neuron.htm 9 January 2010 15:13 UTC www.holisticeducator.com [Source type: Academic]
  
  ^ Neuron preparation by Ramón y Cajal .
  • Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]
  
  Cambridge University Press, Cambridge.
• Peters, A., Palay, S.L., Webster, H, D., 1991 The Fine Structure of the Nervous System, 3rd ed., Oxford, New York

External links

• NeuronBank an online neuromics tool for cataloging neuronal types and synaptic connectivity.
• High Resolution Neuroanatomical Images of Primate and Non-Primate Brains.
• The Department of Neuroscience at Wikiversity, which presently offers two courses: Fundamentals of Neuroscience and Comparative Neuroscience.
• NIF Search - Renshaw Cell via the Neuroscience Information Framework
• Cell Centered Database - Neuron
• NeuroMorpho.Org an online database of digital reconstructions of neuronal morphology.
• Immunohistochemistry Image Gallery: Neuron

Histology: nervous tissue (TA A14.2.00, GA 9.849) Neurons (grey matter) Parts soma axon (axon hillock, axon terminals, axoplasm, axolemma, neurofibril/neurofilament) dendrite (Nissl body, dendritic spine, apical dendrite, basal dendrite) Types bipolar · pseudounipolar · multipolar · pyramidal · Purkinje · granule Afferent nerve fiber/ Sensory nerve GSA · GVA · SSA · SVA fibers (Ia, Ib or Golgi, II or Aβ, III or Aδ or fast pain, IV or C or slow pain) Efferent nerve fiber/ Motor nerve GSE · GVE · SVE Upper motor neuron · Lower motor neuron (α motorneuron, γ motorneuron) Termination Synapses neuropil · synaptic vesicle Interneuron (Renshaw) · neuromuscular junction · electrical synapse Sensory receptors Meissner's corpuscle · Merkel nerve ending · Pacinian corpuscle · Ruffini ending · Muscle spindle · Free nerve ending · Olfactory receptor neuron · Photoreceptor cell · Hair cell · Taste bud Support Glial cells Astrocyte (Radial glia) · Oligodendrocyte · Ependymal cells (Tanycytes) · Microglia Myelination (white matter) CNS: Oligodendrocyte PNS: Schwann cell · Neurolemma · Nodes of Ranvier/Internode · Schmidt-Lanterman incisures Related connective tissues epineurium · perineurium · endoneurium · nerve fascicle · meninges Other Posterior (Root, Ganglion, Ramus) · Anterior (Root, Ramus) · rami communicantes (Gray, White) · Preganglionic fibers · Postganglionic fibers · Lemniscus · Funiculus · Fasciculus · Decussation · Commissure Projection fibers · Association fiber · Commissural fiber peripheral nervous system navs: anat/histo/physio/dev, noncongen PNS somatic/autonomic/congen/neoplasia, symptoms+signs/eponymous, proc

Categories: Neurons | Nervous system | Medical terms

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