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Neuron: neuron (Nerve Cell)
neuron (Nerve Cell) - Drawing by Santiago Ramón y Cajal of neurons in the pigeon cerebellum. <a name=.(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
.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 electrochemical signaling, via connections with other cells called synapses.^ The action potential transfers to synapsed neurons that connect to the optic nerve.

^ These signals are transmitted from neuron (nerve cell) to neuron across "synapses."
  • Neuroscience for Kids - Models 9 January 2010 15:13 UTC faculty.washington.edu [Source type: FILTERED WITH BAYES]

^ Neurons transmit nerve messages.

.Neurons are the core components of the nervous system, which includes the brain, spinal cord, and peripheral ganglia.^ The central nervous system includes the brain and spinal cord.

^ The brain and spinal cord should be easy.
  • Neuroscience for Kids - Models 9 January 2010 15:13 UTC faculty.washington.edu [Source type: FILTERED WITH BAYES]

^ The Central Nervous System (CNS) is composed of the brain and spinal cord.

.A number of specialized types of neurons exist: sensory neurons respond to touch, sound, light and numerous other stimuli affecting cells of the sensory organs that then send signals to the spinal cord and brain.^ The brain and spinal cord should be easy.
  • Neuroscience for Kids - Models 9 January 2010 15:13 UTC faculty.washington.edu [Source type: FILTERED WITH BAYES]

^ There are two types of cells in the brain; neurons and glia.

^ Cajal pointed out that the brains of more highly developed animals contain more Golgi Type II cells than Golgi Type I cells; and that the main difference between the mouse and primate cortex was in the relative number of Golgi Type II neurons.

.Motor neurons receive signals from the brain and spinal cord and cause muscle contractions and affect glands.^ The brain and spinal cord should be easy.
  • Neuroscience for Kids - Models 9 January 2010 15:13 UTC faculty.washington.edu [Source type: FILTERED WITH BAYES]

^ Each muscle fiber of skeletal muscle is innervated by a single spinal motor neuron.
  • Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ Using your reference slides, the best view of "whole" neurons is provided by the slide labelled "nerve cells, ox spinal cord".
  • Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

.Interneurons connect neurons to other neurons within the same region of the brain or spinal cord.^ The brain and spinal cord should be easy.
  • Neuroscience for Kids - Models 9 January 2010 15:13 UTC faculty.washington.edu [Source type: FILTERED WITH BAYES]

^ All other neurons are interneurons .
  • Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ Long-axon neurons are responsible for communicating with other brain regions.
  • Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

.A typical neuron possesses a cell body (often called soma), dendrites, and an axon.^ This enzyme is found throughout the cell body, dendrites and axon of spinal motor neurons.
  • Normal Motor Neurons 6 February 2010 12:41 UTC www.med.unc.edu [Source type: Academic]

^ 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]

^ How different are the proteins in the motor neuron cell body and motor axon?
  • Normal Motor Neurons 6 February 2010 12:41 UTC www.med.unc.edu [Source type: Academic]

.Dendrites are filaments of protoplasm that extrude from the cell body, often extending for hundreds of microns and branching multiple times, giving rise to a complex "dendritic tree". An axon is a special protoplasmic filament that arises from the cell body at a site called the axon hillock and travels through the body, often for a great distance.^ 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]

^ 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 cell body of a neuron frequently gives rise to multiple dendrites, but never to more than one axon, although the axon may branch hundreds of times before it terminates.^ 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]

^ The cell body and synaptic terminal of the neuron can be plastic containers.
  • Neuroscience for Kids - Models 9 January 2010 15:13 UTC faculty.washington.edu [Source type: FILTERED WITH BAYES]

^ Dendrites transmit information to the cell body, and axons transmit messages away from the cell body.

.At the majority of synapses, signals are sent from the axon of one neuron to a dendrite of another.^ The dendrites end in terminals which connect one neuron to another.
  • The Theory of Consciousness 9 January 2010 15:13 UTC neuron4.net [Source type: FILTERED WITH BAYES]

^ This neuron with seven dendrites requires 65 beads: 42 beads for the dendrites, 10 beads for the cell body, 12 beads for the axon and 1 bead for the synaptic terminal.
  • Neuroscience for Kids - Models 9 January 2010 15:13 UTC faculty.washington.edu [Source type: FILTERED WITH BAYES]

^ 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]

.There are, however, many exceptions to these rules: neurons that lack dendrites, neurons that have no axon, synapses that connect an axon to another axon or a dendrite to another dendrite, etc.^ Most synapses are not electrically connected to another neuron.
  • The Theory of Consciousness 9 January 2010 15:13 UTC neuron4.net [Source type: FILTERED WITH BAYES]

^ The dendrites end in terminals which connect one neuron to another.
  • The Theory of Consciousness 9 January 2010 15:13 UTC neuron4.net [Source type: FILTERED WITH BAYES]

^ This procedure is hardwired by connections of neurons and synapses.
  • The Theory of Consciousness 9 January 2010 15:13 UTC neuron4.net [Source type: FILTERED WITH BAYES]

.All neurons are electrically excitable, maintaining voltage gradients across their membranes by means of metabolically driven ion pumps, which combine with ion channels embedded in the membrane to generate intracellular-versus-extracellular concentration differences of ions such as sodium, potassium, chloride, and calcium.^ This imbalance is maintained by the active transport of ions to reset the membrane known as the sodium potassium pump.

^ Sodium ions are more concentrated outside the membrane, while potassium ions are more concentrated inside the membrane.

^ The sodium-potassium pump maintains this unequal concentration by actively transporting ions against their concentration gradients.

.Changes in the cross-membrane voltage can alter the function of voltage-dependent ion channels.^ Sodium gates and potassium gates open in the membrane to allow their respective ions to cross.

^ A general term for an electrophysiological process (currently either a Channel Mechanism , a Synaptic Mechanism or an Ion Concentration ) which is placed on modelled cell membranes or at the interface of two cells to alter their internal electrical and chemical state.
  • Glossary of the main terms used in neuroConstruct 9 January 2010 15:13 UTC www.neuroconstruct.org [Source type: Reference]

^ Released neurotransmitters diffuse across the cleft, and bind to receptors on the other cell's membrane, causing ion channels on that cell to open.

.If the voltage changes by a large enough amount, an all-or-none electrochemical pulse called an action potential is generated, which travels rapidly along the cell's axon, and activates synaptic connections with other cells when it arrives.^ 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]

^ Along myelinated axons, action potentials are regenerated only at the nodes.
  • Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [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]

.Neurons do not undergo cell division, and usually cannot be replaced after being lost, although there are a few known exceptions.^ A few other neurons are generated from Q, G1, H2 and T blast cells.
  • Individual Neuron List 6 February 2010 12:41 UTC wormatlas.org [Source type: Academic]

^ Bovine and human spinal motor neurons usually have a stellate appearance, with their primary dendrites emerging from several points around the circumference of a rounded cell body.
  • Normal Motor Neurons 6 February 2010 12:41 UTC www.med.unc.edu [Source type: Academic]

^ Few cell divisions occur during the L2 stage.
  • Individual Neuron List 6 February 2010 12:41 UTC wormatlas.org [Source type: Academic]

.In most cases they are generated by special types of stem cells, although astrocytes (a type of glial cell) have been observed to turn into neurons as they are sometimes pluripotent.^ A Cell Type which represents a real neuron, but whose morphology is described with a much reduced number of segments.
  • Glossary of the main terms used in neuroConstruct 9 January 2010 15:13 UTC www.neuroconstruct.org [Source type: Reference]

^ Some axons are wrapped in a myelin sheath formed from the plasma membranes of specialized glial cells known as Schwann cells .

^ 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]

Contents

Overview

Structure of a typical neuron
Neuron
At one end of an elongated structure is a branching mass. At the centre of this mass is the nucleus and the branches are dendrites. <a name=.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 .

^ 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.

src="http://images-mediawiki-sites.thefullwiki.org/01/1/9/1/58020532121475006.png" width="400" height="215" />
.A neuron is a special type of cell that is found in the bodies of most animals (all members of the group Eumetazoa, to be precise—this excludes only sponges and a few other very simple animals).^ A few other neurons are generated from Q, G1, H2 and T blast cells.
  • Individual Neuron List 6 February 2010 12:41 UTC wormatlas.org [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]

^ ChAc and AChE activity in bovine lumbar and cervical ventral gray matter is confined to the motor neuron cell bodies and their proximal dendrites.
  • Normal Motor Neurons 6 February 2010 12:41 UTC www.med.unc.edu [Source type: Academic]

.The features that define a neuron are electrical excitability and the presence of synapses, which are complex membrane junctions used to transmit signals to other cells.^ These signals are transmitted from neuron (nerve cell) to neuron across "synapses."
  • Neuroscience for Kids - Models 9 January 2010 15:13 UTC faculty.washington.edu [Source type: FILTERED WITH BAYES]

^ Early investigations by others into the properties of neurons isolated from mature animals indicated that, in addition to the loss of the axon and the distal dendrites, damage also occurred to the plasma membrane of the cell body.
  • Normal Motor Neurons 6 February 2010 12:41 UTC www.med.unc.edu [Source type: Academic]

^ 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]

.The body's neurons, plus the glial cells that give them structural and metabolic support, together constitute the nervous system.^ Cell bodies are in the central nervous system (CNS) or ganglia .

^ Neuroanatomy is the study of the structure of the nervous system.

^ The neuron is the functional unit of the nervous system.

.In vertebrates, the majority of neurons belong to the central nervous system, but some reside in peripheral ganglia, and many sensory neurons are situated in sensory organs such as the retina and cochlea.^ Cell bodies are in the central nervous system (CNS) or ganglia .

^ The neuropil is a dense network of neurons and glia in the central nervous system .

^ The neuron is the functional unit of the nervous system.

.Although neurons are very diverse and there are exceptions to nearly every rule, it is convenient to begin with a schematic description of the structure and function of a "typical" neuron.^ Structure of a typical neuron.

^ 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]

^ Every pulse from the neuron flips it to the excited status, which is a very quick process.
  • The Theory of Consciousness 9 January 2010 15:13 UTC neuron4.net [Source type: FILTERED WITH BAYES]

.A typical neuron is divided into three parts: the soma or cell body, dendrites, and axon.^ The middle part of your body is the "soma" or "cell body."
  • Neuroscience for Kids - Models 9 January 2010 15:13 UTC faculty.washington.edu [Source type: FILTERED WITH BAYES]

^ 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]

^ This enzyme is found throughout the cell body, dendrites and axon of spinal motor neurons.
  • Normal Motor Neurons 6 February 2010 12:41 UTC www.med.unc.edu [Source type: Academic]

.The soma is usually compact; the axon and dendrites are filaments that extrude from 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]

.Dendrites typically branch profusely, getting thinner with each branching, and extending their farthest branches a few hundred microns from the soma.^ A nerve cell typically has several dendrites, each with numerous branches.
  • Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ V.B) Neuron Tracing       Back to Table of Contents 3DMA-Neuron also has the capability of tracing dendtritic trees, providing labeling of separate brushes leaving the soma and of dendritic branch segments.

^ Typical axons have relatively few branches, except near the terminal end.
  • Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

.The axon leaves the soma at a swelling called the axon hillock, and can extend for great distances, giving rise to hundreds of branches.^ 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]

^ V.B) Neuron Tracing       Back to Table of Contents 3DMA-Neuron also has the capability of tracing dendtritic trees, providing labeling of separate brushes leaving the soma and of dendritic branch segments.

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

.Unlike dendrites, an axon usually maintains the same diameter as it extends.^ 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).
  • Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ Extending out from each nerve cell body are long cytoplasmic processes, one axon and several dendrites.
  • 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]

.The soma may give rise to numerous dendrites, but never to more than one axon.^ The axon, even more so than the dendrites, disappears into the distance and cannot be followed to its end.
  • Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

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

^ However, the length of axons and dendrites is wondrously great, far greater than ordinary cellular dimensions.
  • Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

.Synaptic signals from other neurons are received by the soma and dendrites; signals to other neurons are transmitted by the axon.^ 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]

^ The Rope Neuron in Action Materials: Rope (for dendrites and axon) Plastic containers (for cell body and synaptic terminal) Pool Float (or another object will slide along the rope; for the action potential) Plastic balls (for neurotransmitters) Volunteers!
  • Neuroscience for Kids - Models 9 January 2010 15:13 UTC faculty.washington.edu [Source type: FILTERED WITH BAYES]

^ 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]

.A typical synapse, then, is a contact between the axon of one neuron and a dendrite or soma of another.^ 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]

^ The dendrites end in terminals which connect one neuron to another.
  • The Theory of Consciousness 9 January 2010 15:13 UTC neuron4.net [Source type: FILTERED WITH BAYES]

^ This neuron with seven dendrites requires 65 beads: 42 beads for the dendrites, 10 beads for the cell body, 12 beads for the axon and 1 bead for the synaptic terminal.
  • Neuroscience for Kids - Models 9 January 2010 15:13 UTC faculty.washington.edu [Source type: FILTERED WITH BAYES]

Synaptic signals may be excitatory or inhibitory. .If the net excitation received by a neuron over a short period of time is large enough, the neuron generates a brief pulse called an action potential, which originates at the soma and propagates rapidly along the axon, activating synapses onto other neurons as it goes.^ Short-axon neurons are also called intrinsic neurons or local interneurons .
  • Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ Along myelinated axons, action potentials are regenerated only at the nodes.
  • Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ 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]

.Many neurons fit the foregoing schema in every respect, but there are also exceptions to most parts of it.^ 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]

^ Again, there were many differences in the 2-D gel patterns of proteins from ventral gray matter and isolated motor neuron cell bodies, with most cell body proteins visible on the VGM gels, and many VGM proteins not seen on the cell body gels.
  • Normal Motor Neurons 6 February 2010 12:41 UTC www.med.unc.edu [Source type: Academic]

.There are no neurons that lack a soma, but there are neurons that lack dendrites, and others that lack an axon.^ Gray matter is gray not because it lacks myelin, but because it contains lots of other stuff besides myelinated axons.
  • Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ This neuron with seven dendrites requires 65 beads: 42 beads for the dendrites, 10 beads for the cell body, 12 beads for the axon and 1 bead for the synaptic terminal.
  • Neuroscience for Kids - Models 9 January 2010 15:13 UTC faculty.washington.edu [Source type: FILTERED WITH BAYES]

^ 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]

.Furthermore, in addition to the typical axodendritic and axosomatic synapses, there are axoaxonic (axon-to-axon) and dendrodendritic (dendrite-to-dendrite) synapses.^ 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]

^ Sensory neurons typically have a long dendrite and short axon, and carry messages from sensory receptors to the central nervous system .

^ A typical nerve cell body contains only a small fraction of the total cell volume; the rest is contained in the axon and dendrites.
  • Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

.The key to neural function is the synaptic signalling process, which is partly electrical and partly chemical.^ There is a small gap between them, which means an electrical signal has to be converted to a chemical signal and back to an electrical signal before the next neuron can pass it on.
  • The Theory of Consciousness 9 January 2010 15:13 UTC neuron4.net [Source type: FILTERED WITH BAYES]

^ A general term for an electrophysiological process (currently either a Channel Mechanism , a Synaptic Mechanism or an Ion Concentration ) which is placed on modelled cell membranes or at the interface of two cells to alter their internal electrical and chemical state.
  • Glossary of the main terms used in neuroConstruct 9 January 2010 15:13 UTC www.neuroconstruct.org [Source type: Reference]

^ 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]

.The electrical aspect depends on properties of the neuron's membrane.^ Level 2 builds on Level 1 to include specifications for describing passive membrane properties, and the distributions of channels on neuron models.
  • Glossary of the main terms used in neuroConstruct 9 January 2010 15:13 UTC www.neuroconstruct.org [Source type: Reference]

^ The plasma membrane of neurons, like all other cells, has an unequal distribution of ions and electrical charges between the two sides of the membrane.

.Like all animal cells, every neuron is surrounded by a plasma membrane, a bilayer of lipid molecules with many types of protein structures embedded in it.^ 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 cell body is the site of synthesis of all proteins in motor neurons except those proteins that might enter the cell from the outside ( e.g ., by endocytosis, viral infection, etc.
  • Normal Motor Neurons 6 February 2010 12:41 UTC www.med.unc.edu [Source type: Academic]

^ A Cell Type which represents a real neuron, but whose morphology is described with a much reduced number of segments.
  • Glossary of the main terms used in neuroConstruct 9 January 2010 15:13 UTC www.neuroconstruct.org [Source type: Reference]

.A lipid bilayer is a powerful electrical insulator, but in neurons, many of the protein structures embedded in the membrane are electrically active.^ Neurons consume a lot of energy, and the glial cells help neurons with energy supply, supply of other chemicals, storage, structural support, electrical insulation and waste removal.
  • The Theory of Consciousness 9 January 2010 15:13 UTC neuron4.net [Source type: FILTERED WITH BAYES]

^ The neurons are covered by an insulating, lipid-based coating, called the myelin sheath, which prevents stray neural signals from passing to other neurons or to other tissues.

^ Again, there were many differences in the 2-D gel patterns of proteins from ventral gray matter and isolated motor neuron cell bodies, with most cell body proteins visible on the VGM gels, and many VGM proteins not seen on the cell body gels.
  • Normal Motor Neurons 6 February 2010 12:41 UTC www.med.unc.edu [Source type: Academic]

.These include ion channels that permit electrically charged ions to flow across the membrane, and ion pumps that actively transport ions from one side of the membrane to the other.^ Passage of ions across the cell membrane passes the electrical charge along the cell.

^ Then connect each dot on one side with the 10 dots on the other side.
  • Neuroscience for Kids - Models 9 January 2010 15:13 UTC faculty.washington.edu [Source type: FILTERED WITH BAYES]

^ (Neurotransmission can also be electrical, with ions passing directly from one cell into another.
  • Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

.Most ion channels are permeable only to specific types of ions.^ 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]

^ 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]

^ ChannelML seeks to separate the electrophysiological data from any specific implementation, defining a template for numerous types of cellular mechanism, containing only the relevant biophysical parameters (e.g.
  • Glossary of the main terms used in neuroConstruct 9 January 2010 15:13 UTC www.neuroconstruct.org [Source type: Reference]

.Some ion channels are voltage gated, meaning that they can be switched between open and closed states by altering the voltage difference across the membrane.^ A narcotic is a brain dulling and analgesic drug, not a sleep inducing drug as many believe, there is a notable difference between a state of sleep and a state of a dulled brain .

.Others are chemically gated, meaning that they can be switched between open and closed states by interactions with chemicals that diffuse through the extracellular fluid.^ Rewarded Outcomes Enhance Reactivation of Experience in the Hippocampus We used a sequence switching task that allowed us to examine the interaction between SWRs and reward.
  • Pubget: Neuron[latest] 9 January 2010 15:13 UTC pubget.com [Source type: Academic]

^ There is a small gap between them, which means an electrical signal has to be converted to a chemical signal and back to an electrical signal before the next neuron can pass it on.
  • The Theory of Consciousness 9 January 2010 15:13 UTC neuron4.net [Source type: FILTERED WITH BAYES]

^ So, I have problems neither with Ramachandran's opening questions, nor with his closing remarks (other than the very last sentence: "I regard Rizzolati's discovery ...
  • The Reality Club: Mirror Neurons 6 February 2010 12:41 UTC www.edge.org [Source type: Original source]

.The interactions between ion channels and ion pumps produce a voltage difference across the membrane, typically a bit less than 1/10 of a volt at baseline.^ How is it different than the post-synaptic membrane.
  • MEPP, EPP and acetylcholine help | Allopathic | Student Doctor Network 9 January 2010 15:13 UTC forums.studentdoctor.net [Source type: General]

.This voltage has two functions: first, it provides a power source for an assortment of voltage-dependent protein machinery that is embedded in the membrane; second, it provides a basis for electrical signal transmission between different parts of the membrane.^ Embedment-free, unstained thin sections provide a very different view of the motor neuron cytoskeleton than conventional Epon-embedded, stained thin sections.
  • Normal Motor Neurons 6 February 2010 12:41 UTC www.med.unc.edu [Source type: Academic]

^ There is a small gap between them, which means an electrical signal has to be converted to a chemical signal and back to an electrical signal before the next neuron can pass it on.
  • The Theory of Consciousness 9 January 2010 15:13 UTC neuron4.net [Source type: FILTERED WITH BAYES]

.Neurons communicate by chemical and electrical synapses in a process known as synaptic transmission.^ This giant model of a neuron illustrates the properties of chemical transmission and the action potential .
  • Neuroscience for Kids - Models 9 January 2010 15:13 UTC faculty.washington.edu [Source type: FILTERED WITH BAYES]

^ Neurons consume a lot of energy, and the glial cells help neurons with energy supply, supply of other chemicals, storage, structural support, electrical insulation and waste removal.
  • The Theory of Consciousness 9 January 2010 15:13 UTC neuron4.net [Source type: FILTERED WITH BAYES]

^ Most synapses are not electrically connected to another neuron.
  • The Theory of Consciousness 9 January 2010 15:13 UTC neuron4.net [Source type: FILTERED WITH BAYES]

.The fundamental process that triggers synaptic transmission is the action potential, a propagating electrical signal that is generated by exploiting the electrically excitable membrane of the neuron.^ Transmission of an action potential down an axon .

^ The fundamental process underlying synaptic transmission is the action potential , a propagating electrical signal that is generated by exploiting the electrically excitable membrane of the neuron.
  • Neuron - BBWiki 6 February 2010 12:41 UTC bbwiki.tamu.edu [Source type: Reference]

^ Then, the neuron fires an action potential.

This is also known as a wave of depolarization.

Anatomy and histology

Diagram of a typical myelinated vertebrate motoneuron.
.Neurons are highly specialized for the processing and transmission of cellular signals.^ Neurons are highly specialized for the fast processing and transmission of cellular signals..

^ The fundamental process that triggers synaptic transmission is the action potential, a propagating electrical signal that is generated by exploiting the electrically excitable membrane of the neuron.

^ Calcium Imaging of Cortical Neurons using Fura-2 AM Calcium signals play a key role in many cellular processes including gene expression, survival and differentiation.
  • JoVE Browse:Keyword Search: neurons 6 February 2010 12:41 UTC www.jove.com [Source type: Academic]

.Given the diversity of functions performed by neurons in different parts of the nervous system, there is, as expected, a wide variety in the shape, size, and electrochemical properties of neurons.^ Neurons exist in many shapes and sizes.
  • Neuron - Structure And Function, Structural Classification, Glial Cells, Functional Classification 9 January 2010 15:13 UTC science.jrank.org [Source type: Academic]

^ The neuron is the basic functional unit of the nervous system .
  • neuron@Everything2.com 9 January 2010 15:13 UTC www.everything2.com [Source type: FILTERED WITH BAYES]

^ After the different parts of a neuron has been covered, move on to the function of a neuron.
  • Lesson Plan on the Human Brain : Neurons in the Brain 6 February 2010 12:41 UTC www.brighthub.com [Source type: Academic]

For instance, the soma of a neuron can vary from 4 to 100 micrometers in diameter.[1]
  • 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 .

    ^ 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.

    .The nucleus ranges from 3 to 18 micrometers in diameter.^ The nucleus ranges from 3 to 18 micrometers in diameter.

    ^ 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.

    ^ The soma is usually about 10–25 micrometers in diameter and often is not much larger than the cell nucleus it contains.

    [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.
.Although the canonical view of the neuron attributes dedicated functions to its various anatomical components, dendrites and axons often act in ways contrary to their so-called main function.^ Describe the components of the neuron and their function.
  • Neuropsychology/Behavioral Neuroscience Home 9 January 2010 15:13 UTC neuro.psyc.memphis.edu [Source type: Academic]

^ Neurons have specialized projections called dendrites and axons .
  • Neuroscience For Kids - questions/answers 6 February 2010 12:41 UTC staff.washington.edu [Source type: FILTERED WITH BAYES]

^ Neurons have two ends: axons and dendrites.

.Axons and dendrites in the central nervous system are typically only about one micrometer thick, while some in the peripheral nervous system are much thicker.^ 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]

^ For most of the nineteenth century, there was an on-going debate among researchers about the organization of the nervous system.
  • The discovery of the neuron : Neurophilosophy 6 February 2010 12:41 UTC scienceblogs.com [Source type: FILTERED WITH BAYES]

^ 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]

.The soma is usually about 10–25 micrometers in diameter and often is not much larger than the cell nucleus it contains.^ 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]

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

^ This allows humans to adapt to different environments to a much larger degree than most animals, which usually require a very specific environment to survive.
  • The Theory of Consciousness 9 January 2010 15:13 UTC neuron4.net [Source type: FILTERED WITH BAYES]

The longest axon of a human motoneuron can be over a meter long, reaching from the base of the spine to the toes. .Sensory neurons have axons that run from the toes to the dorsal columns, over 1.5 meters in adults.^ Sensory neurons have axons that run from the toes to the dorsal columns , over 1.5 meters in adults.

^ Nerve cells or neurons were taken from adult rats, specifically from the dorsal root ganglion - a set of nerve cells that is located just outside the spinal cord and that relays sensory information like temperature and pressure from skin and muscles to the brain.
  • rings: University of Utah News Release: January xx, 2002 20 September 2009 18:16 UTC www.utah.edu [Source type: FILTERED WITH BAYES]

^ The voltage runs along the axons and into the dendrites of connected cells, perhaps as many as 10,000 other neurons.

.Giraffes have single axons several meters in length running along the entire length of their necks.^ The diameter of an axon is uniform along its entire length.
  • Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ To myelinate the entire length of the axon, many of these Schwann cell wrappings line up end-to-end along the axon.
  • Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ Axon length may exceed a meter (for many sensory and motor axons), and commonly extends for several centimeters.
  • Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

.Much of what is known about axonal function comes from studying the squid giant axon, an ideal experimental preparation because of its relatively immense size (0.5–1 millimeters thick, several centimeters long).^ The study of neuroanatomy is largely the study of the axonal projections of long-axon cells.
  • Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ These data prompted us to study a number of structural and functional characteristics of motor neurons of different sizes as a means to understand the biological significance of those differences.
  • Normal Motor Neurons 6 February 2010 12:41 UTC www.med.unc.edu [Source type: Academic]

^ Dendrites may extend several millimeters away from the cell body, into a volume the size of a pea.
  • Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

.Fully differentiated neurons are permanently amitotic;[3] however, recent research shows that additional neurons throughout the brain can originate from neural stem cells found throughout the brain but in particularly high concentrations in the subventricular zone and subgranular zone through the process of neurogenesis.^ 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]

^ Besides neurons, which make up only about 10% of the brains mass, it contains glial cells.
  • The Theory of Consciousness 9 January 2010 15:13 UTC neuron4.net [Source type: FILTERED WITH BAYES]

^ We found, however, that one can achieve over two orders of magnitude higher labeling in frog motor neurons by exposing the spinal cord to the radioactive precursor first and then isolating the labeled cell bodies.
  • Normal Motor Neurons 6 February 2010 12:41 UTC www.med.unc.edu [Source type: Academic]

[4]

Histology and internal structure

Golgi-stained neurons in human hippocampal tissue.
.Nerve cell bodies stained with basophilic dyes show numerous microscopic clumps of Nissl substance (named after German psychiatrist and neuropathologist Franz Nissl, 1860–1919), which consists of rough endoplasmic reticulum and associated ribosomal RNA.^ Nissl substance (rough endoplasmic reticulum).
  • Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

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

^ To confirm the presence of ribosomes, we performed confocal imaging of cell body cytoskeletons isolated from human motor neurons stained with methylene blue, which binds to RNA. Human motor neurons contain well-formed Nissl bodies, which were easily visualized by light microscopy when stained with basophilic dyes.
  • Normal Motor Neurons 6 February 2010 12:41 UTC www.med.unc.edu [Source type: Academic]

.The prominence of the Nissl substance can be explained by the fact that nerve cells are metabolically very active, and hence are involved in large amounts of protein synthesis.^ Large cells have several different possible strategies to increase their synthesis of proteins.
  • Normal Motor Neurons 6 February 2010 12:41 UTC www.med.unc.edu [Source type: Academic]

^ The relative amounts of most of these proteins have been estimated for cell bodies isolated from frog ( Sinicropi and McIlwain, 1983 ) and bovine tissue ( Brock and McIlwain, 1985 ).
  • Normal Motor Neurons 6 February 2010 12:41 UTC www.med.unc.edu [Source type: Academic]

^ The cell body is the site of synthesis of all proteins in motor neurons except those proteins that might enter the cell from the outside ( e.g ., by endocytosis, viral infection, etc.
  • Normal Motor Neurons 6 February 2010 12:41 UTC www.med.unc.edu [Source type: Academic]

.The cell body of a neuron is supported by a complex meshwork of structural proteins called neurofilaments, which are assembled into larger neurofibrils.^ The cell body of a neuron is supported by a complex meshwork of structural proteins called neurofilaments , which are assembled into larger neurofibrils .

^ What are the major proteins in the cell body cytoskeleton?
  • Normal Motor Neurons 6 February 2010 12:41 UTC www.med.unc.edu [Source type: Academic]

^ How different are the proteins in the motor neuron cell body and motor axon?
  • Normal Motor Neurons 6 February 2010 12:41 UTC www.med.unc.edu [Source type: Academic]

.Some neurons also contain pigment granules, such as neuromelanin (a brownish-black pigment, byproduct of synthesis of catecholamines) and lipofuscin (yellowish-brown pigment that accumulates with age).^ Parkinson's disease ( WebPath ) involves loss of the pigmented neurons in the brainstem which give substantia nigra ("black substance) its distinctive appearance.
  • Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ Lipofuscin granules are a prominent feature of adult human motor neuron cell bodies and are retained by the isolated cytoskeleton .
  • Normal Motor Neurons 6 February 2010 12:41 UTC www.med.unc.edu [Source type: Academic]

.There are different internal structural characteristics between axons and dendrites.^ There are different internal structural characteristics between axons and dendrites.

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

^ For example, axons in the internal capsule and corpus callosum crisscross back and forth, interconnecting many different regions of the cerebral hemispheres.
  • Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

Typical axons almost never contain ribosomes, except some in the initial segment. .Dendrites contain granular endoplasmic reticulum or ribosomes, with diminishing amounts with distance from the cell body.^ Dendrites contain granular endoplasmic reticulum or ribosomes , with diminishing amounts with distance from the cell body.

^ Gray matter is the cell bodies and dendrites.
  • Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ Nerve cell bodies stained with basophilic dyes show numerous microscopic clumps of Nissl substance (named after German psychiatrist and neuropathologist Franz Nissl , 1860–1919), which consists of rough endoplasmic reticulum and associated ribosomes .

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.

Source PLoS Biology [1]
SMI32-stained pyramidal neurons in cerebral cortex.
.Neurons exist in a number of different shapes and sizes and can be classified by their morphology and function.^ Further evidence that the RNA-rich cytoskeleton we isolate maintains motor neuronal size and shape is presented below .
  • Normal Motor Neurons 6 February 2010 12:41 UTC www.med.unc.edu [Source type: Academic]

^ These data prompted us to study a number of structural and functional characteristics of motor neurons of different sizes as a means to understand the biological significance of those differences.
  • Normal Motor Neurons 6 February 2010 12:41 UTC www.med.unc.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]

.The anatomist Camillo Golgi grouped neurons into two types; type I with long axons used to move signals over long distances and type II with short axons, which can often be confused with dendrites.^ 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]

^ The axon, even more so than the dendrites, disappears into the distance and cannot be followed to its end.
  • Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ The axons of a region's long-axon neurons are by definition identical with the region's efferent axons .
  • Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

.Type I cells can be further divided by where the cell body or soma is located.^ The middle part of your body is the "soma" or "cell body."
  • Neuroscience for Kids - Models 9 January 2010 15:13 UTC faculty.washington.edu [Source type: FILTERED WITH BAYES]

^ The later use of cryoprotection further increased the total protein content of the isolated cell bodies and reduced the loss of newly synthesized proteins from them ( Sinicropi et al.
  • Normal Motor Neurons 6 February 2010 12:41 UTC www.med.unc.edu [Source type: Academic]

^ Cell bodies of sensory axons occur in dorsal root ganglia, located near the cord along the dorsal root.
  • Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

.The basic morphology of type I neurons, represented by spinal motor neurons, consists of a cell body called the soma and a long thin axon which is covered by the myelin sheath.^ This enzyme is found throughout the cell body, dendrites and axon of spinal motor neurons.
  • Normal Motor Neurons 6 February 2010 12:41 UTC www.med.unc.edu [Source type: Academic]

^ What are the solubility properties of the cytoskeleton in motor neuron cell bodies?
  • 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]

.Around the cell body is a branching dendritic tree that receives signals from other neurons.^ Gray matter is the cell bodies and dendrites.
  • 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]

^ 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 end of the axon has branching terminals (axon terminal) that release neurotransmitters into a gap called the synaptic cleft between the terminals and the dendrites of the next neuron.^ 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]

^ The third neuron then places its neurotransmitter into the dendrites of the next neuron and the "signal" travels to the end of the line.
  • Neuroscience for Kids - Models 9 January 2010 15:13 UTC faculty.washington.edu [Source type: FILTERED WITH BAYES]

^ Once this message is received, this second neuron places its neurotransmitter into the dendrite of the next neuron.
  • Neuroscience for Kids - Models 9 January 2010 15:13 UTC faculty.washington.edu [Source type: FILTERED WITH BAYES]

Structural classification

Polarity

Most neurons can be anatomically characterized as:

Other

.Furthermore, some unique neuronal types can be identified according to their location in the nervous system and distinct shape.^ 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]

^ Nervous system: V5.pa generates the postdeirid sensilla and G2 produces two ventral ganglion neurons.
  • Individual Neuron List 6 February 2010 12:41 UTC wormatlas.org [Source type: Academic]

Some examples are:

Functional classification

Direction

.Afferent and efferent can also refer generally to neurons which, respectively, bring information to or send information from the brain region.^ These terms may often correlate with " afferent " and " efferent ", at least when the reference is high, like cortex.
  • Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ The axons of a region's long-axon neurons are by definition identical with the region's efferent axons .
  • 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]

Action on other neurons

.A neuron affects other neurons by releasing a neurotransmitter that binds to chemical receptors.^ This models the release of neurotransmitters and the attachment (binding) of neurotransmitters to receptors on dendrites.
  • Neuroscience for Kids - Models 9 January 2010 15:13 UTC faculty.washington.edu [Source type: FILTERED WITH BAYES]

^ 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]

^ Neurotransmission is usually chemical, based on small molecules called neurotransmitters , secreted by one cell and binding to another.
  • Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

.The effect upon the target neuron is determined not by the source neuron or by the neurotransmitter, but by the type of receptor that is activated.^ 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]

A neurotransmitter can be thought of as a key, and a receptor as a lock: the same type of key can here be used to open many different types of locks. Receptors can be classified broadly as excitatory (causing an increase in firing rate), inhibitory (causing a decrease in firing rate), or modulatory (causing long-lasting effects not directly related to firing rate).
In fact, however, the two most common neurotransmitters in the brain, glutamate and GABA, have actions that are largely consistent. Glutamate acts on several different types of receptors, but most of them have effects that are excitatory. Similarly GABA acts on several different types of receptors, but all of them have effects (in adult animals, at least) that are inhibitory. .Because of this consistency, it is common for neuroscientists to simplify the terminology by referring to cells that release glutamate as "excitatory neurons," and cells that release GABA as "inhibitory neurons."^ Using your reference slides, the best view of "whole" neurons is provided by the slide labelled "nerve cells, ox spinal cord".
  • Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

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

^ Because nuclear and cell body size are positively correlated, the size of nuclei obtained from isolated motor neuron cell bodies can be used as an indication of the size of its parent motor neuron.
  • Normal Motor Neurons 6 February 2010 12:41 UTC www.med.unc.edu [Source type: Academic]

.Since well over 90% of the neurons in the brain release either glutamate or GABA, these labels encompass the great majority of neurons.^ I know that's a difficult concept to wrap your brain around, since one > > > neuron can only go so far, but it really is that simple.
  • 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]

^ These cells are also called "lower motor neurons", or just "motor neurons" (since upper moter neurons are properly called interneurons).
  • Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ I know that's a difficult concept to wrap your brain around, since one > > neuron can only go so far, but it really is that simple.
  • 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]

.There are also other types of neurons that have consistent effects on their targets, for example "excitatory" motor neurons in the spinal cord that release acetylcholine, and "inhibitory" spinal neurons that release glycine.^ The muscles receive input from the neurons by sending muscle arms to motor neuron processes that run along the nerve cords or reside in the nerve ring.
  • Individual Neuron List 6 February 2010 12:41 UTC wormatlas.org [Source type: Academic]

^ Using your reference slides, the best view of "whole" neurons is provided by the slide labelled "nerve cells, ox spinal cord".
  • Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ One side of the spinal cord was used for a 2h pulse to label the motor neurons and the other side, also labeled during that 2h period, was then “chased” with cold leucine for periods of 15 -180 min.
  • Normal Motor Neurons 6 February 2010 12:41 UTC www.med.unc.edu [Source type: Academic]

The distinction between excitatory and inhibitory neurotransmitters is not absolute, however. .Rather, it depends on the class of chemical receptors present on the target neuron.^ Primary sensory neurons receive their information directly through sense receptors rather than dendrites.
  • Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

.In principle, a single neuron, releasing a single neurotransmitter, can have excitatory effects on some targets, inhibitory effects on others, and modulatory effects on others still.^ 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]

^ 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]

For example, photoreceptors in the retina constantly release the neurotransmitter glutamate in the absence of light. .So-called OFF bipolar cells are, like most neurons, excited by the released glutamate.^ These cells are also called "lower motor neurons", or just "motor neurons" (since upper moter neurons are properly called interneurons).
  • Neurons and Support Cells 9 January 2010 15:13 UTC www.siumed.edu [Source type: Academic]

^ Male specific cell, ventral cord, neuron-like but lacks synapses .
  • Individual Neuron List 6 February 2010 12:41 UTC wormatlas.psc.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]

.However, neighboring target neurons called ON bipolar cells are instead inhibited by glutamate, because they lack the typical ionotropic glutamate receptors and instead express a class of inhibitory metabotropic glutamate receptors.^ 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]

^ However, If chimps are closer to humans than to gorillas, but Gorillas > > > > > and Chimps can not share an ERV unless the ERV is also present in > > > > > humans because they all share a common ancestor, then finding an ERV > > > > > in chimps and gorillas, but not in humans falsifies evolution.
  • 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]

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

[5] When light is present, the photoreceptors cease releasing glutamate, which relieves the ON bipolar cells from inhibition, activating them; this simultaneously removes the excitation from the OFF bipolar cells, silencing them.

Discharge patterns

Neurons can be classified according to their electrophysiological characteristics:
.
  • Tonic or regular spiking.^ Tonic or regular spiking .

    .Some neurons are typically constantly (or tonically) active.^ Some neurons are typically constantly (or tonically) active.

    ^ 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.

    ^ 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 that fire in bursts are called phasic.
  • Fast spiking.^ Neurons that fire in bursts are called phasic.

    ^ Some neurons are notable for their fast firing rates, for example some types of cortical inhibitory interneurons, cells in globus pallidus.

    ^ 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.

    ^ Classification by action on other neurons .

    ^ Action potentials of some neurons are more narrow compared to the others.

    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
.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.
.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).
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]

.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.
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

.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.

^ Inhibitory neurons inhibit their target neurons.

^ Excitatory neurons excite their target neurons.

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

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

.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.

^ 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.

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.

^ 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.

^ 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.

^ 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.

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

^ 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.

^ 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 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.

[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.

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

^ 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 .

^ 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.

^ 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.

^ 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.

^ 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

.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

.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

  1. ^ Davies, Melissa (2002-04-09). "The Neuron: size comparison". Neuroscience: A journey through the brain. http://www.ualberta.ca/~neuro/OnlineIntro/NeuronExample.htm. Retrieved 2009-06-20. 
  2. ^ Chudler, Eric H.. "Brain Facts and Figures". Neuroscience for Kids. http://faculty.washington.edu/chudler/facts.html. Retrieved 2009-06-20. 
  3. ^ Herrup K, Yang Y (May 2007). "Cell cycle regulation in the postmitotic neuron: oxymoron or new biology?". Nat. Rev. Neurosci. 8 (5): 368–78. doi:10.1038/nrn2124. PMID 17453017. 
  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. 
  5. ^ Gerber U (2003). "Metabotropic glutamate receptors in vertebrate retina". Doc Ophthalmol 106 (1): 83–87. doi:10.1023/A:1022477203420. PMID 12675489. http://www.springerlink.com/content/m748132506x00lm4/. 
  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
  8. ^ Drachman D (2005). "Do we have brain to spare?". Neurology 64 (12): 2004–5. doi:10.1212/01.WNL.0000166914.38327.BB. PMID 15985565. 
  9. ^ Chudler, Eric H.. "Milestones in Neuroscience Research". Neuroscience for Kids. http://faculty.washington.edu/chudler/hist.html. Retrieved 2009-06-20. 
  10. ^ Patlak, Joe; Gibbons, Ray (2000-11-01). "Electrical Activity of Nerves". Aps in Nerve Cells. http://physioweb.med.uvm.edu/cardiacep/EP/nervecells.htm. Retrieved 2009-06-20. 
  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. 
  14. ^ Witcher M, Kirov S, Harris K (2007). "Plasticity of perisynaptic astroglia during synaptogenesis in the mature rat hippocampus". Glia 55 (1): 13–23. doi:10.1002/glia.20415. PMID 17001633. 
  15. ^ Connors B, Long M (2004). "Electrical synapses in the mammalian brain". Annu Rev Neurosci 27: 393–418. doi:10.1146/annurev.neuro.26.041002.131128. PMID 15217338. 
  16. ^ Sabbatini R.M.E. April-July 2003. Neurons and Synapses: The History of Its Discovery. Brain & Mind Magazine, 17. Retrieved on March 19, 2007.
  17. ^ Djurisic M, Antic S, Chen W, Zecevic D (2004). "Voltage imaging from dendrites of mitral cells: EPSP attenuation and spike trigger zones". J Neurosci 24 (30): 6703–14. doi:10.1523/JNEUROSCI.0307-04.2004. PMID 15282273. 
  18. ^ a b Williams RW, Herrup K (1988). "The control of neuron number". Annual Review of Neuroscience 11: 423–53. doi:10.1146/annurev.ne.11.030188.002231. PMID 3284447. 
  19. ^ Azevedo FA, Carvalho LR, Grinberg LT, et al. (April 2009). "Equal numbers of neuronal and nonneuronal cells make the human brain an isometrically scaled-up primate brain". The Journal of Comparative Neurology 513 (5): 532–41. doi:10.1002/cne.21974. PMID 19226510. 

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.

    ^ 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.

    ^ 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


Wiktionary

Up to date as of January 15, 2010

Definition from Wiktionary, a free dictionary

See also neuron

Contents

English

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Wikipedia has an article on:

Proper noun

Singular
Neuron
Plural
-
Neuron
  1. title of a peer reviewed journal established in 1988 by publisher Cell Press

German

Noun

Neuron n.
  1. (cytology) neuron

Synonyms

  • Nervenzelle

Simple English

[[File:|thumb|right|230px|diagram of neuron]] [[File:|thumb|right|230px|diagram of neuron]] Neurons are also called nerve cells. Neurons are the basic units of the nervous system and its most important part, the brain.

Every neuron has a cell body (sometimes called a soma) and nerve fibres (called axons and dendrites). There are about 100 billion neurons in the human brain.

Contents

Types of neurons

By connection

There are three classes of neurons: afferent neurons, efferent neurons, and interneurons.

By function

Sensory neurons carry signals from sense organs to the spinal cord and brain.

Relay neurons carry messages from one part of the CNS.

Motor neurons carry signals from the CNS to muscles, motor neurons are connected to the relay neurons. The signal passes between the neurons via synapses. Synapses are microscopic voids between cells where chemicals are released from the axon terminal of one cell to specialized chemical receptors on the dendrite of the receiving cell.

Other websites

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Citable sentences

Up to date as of December 23, 2010

Here are sentences from other pages on Neuron, which are similar to those in the above article.








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