#REDIRECT Neuron
Neurons (also spelled neurones or called nerve cells) are the primary cell (biology) of the nervous system. In vertebrates, they are found in the brain, the spinal cord and in the nerves and ganglion of the peripheral nervous system. ==Classes== There are three classes of neurons: afferent neurons, efferent neurons, and interneurons. *Afferent neurons convey information from tissues and organs into the central nervous system. *Efferent neurons transmit signals from the central nervous system to the effector cells. *Interneurons connect neurons within the central nervous system. ==Anatomy and histology==
Many highly specialized types of neurons exist, and these differ widely in appearance. Characteristically, neurons are highly asymmetric in shape. Neurons consist of: *The soma_(biology), or cell-body, the relatively large central part of the cell between the dendrites and the axon. *The axon, a much finer, cable-like projection which may extend tens, hundreds, or even tens of thousands of times the diameter of the soma in length. This is the structure which carries nerve signals away from the neuron. Each neuron has only one axon, but this axon may undergo extensive branching and thereby enable communication with many target cells. *The dendrite, a short, branching arbor of cellular extensions. Each neuron has very many dendrites with profuse dendritic branches. These structures form the main information receiving network for the neuron. Axon and dendrites alike are typically only about a micrometre thick, while the soma is usually about 25 micrometres in diameter and not much larger than than the cell nucleus it contains. The axon of a human motoneuron can be over a metre long, reaching from the base of the spine to the toes, while girraffes have single axons running along the whole length of its neck, which is several feet. ==Connectivity== Neurons communicate with one another and to other cells through synapses, where the axon tip of one cell impinges upon a dendrite or soma of another, or less commonly to an axon. Neurons of the cortex in mammals, such as the Purkinje cells, can have over 1000 dendrites each, enabling connections with tens of thousands of other cells. ==Types of signalling== Neurons communicate with one another across synapses. This communication is usually chemically mediated by exocytosis of neurotransmitter molecules. Pre-synaptic neurons (i.e.the neurons which release the neurotransmitter) may produce in the post-synaptic neurons (i.e. the neurons being affected by the neurotransmitter) an electrical stimulation (an ''electrical excitation'') which will spread to the axon hillock generating an ''action potential'' which then travels as a wave of electrical excitation along the axon. Arrival of an action potential at the tip of an axon triggers the release of neurotransmitter at a synapse. Neurotransmitters can either stimulate or suppress (inhibit) the electrical excitability of a target cell. An action potential will only be triggered in the target cell if neurotransmitter molecules acting on their post-synaptic transmembrane receptor cause the cell to reach its threshold potential. Another less common form of communication between neurons is through electrical synapses mediated by gap junctions. ==Adaptations to carrying action potentials== The narrow cross-section of axons and dendrites lessens the metabolic expense of carrying action potentials, although thicker axons convey the impulses more rapidly, generally speaking. Many neurons have insulating sheaths of myelin around their axons. The sheaths are formed by glial cells: oligodendrocytes in the central nervous system and Schwann cells in the peripheral nervous system. The sheath enables the action potentials to travel saltatory conduction than in unmyelinated axons of the same diameter whilst simultaneously preventing short circiuts amoungst intersecting neurons. The myelin sheath in peripheral nerves normally runs along the axon in sections about 1 mm long, punctuated by unsheathed node of Ranvier. Multiple sclerosis is a neurological disorder which results from abnormal demyelination of peripheral nerves. Neurons with demyelinated axons do not conduct electrical signals properly. Neurons and glia make up the two chief cell types of the central nervous system. There are far more glial cells than neurons, and recent experimental results have suggested that glial cells play a vital role in information processing among neurons. == Histology and internal structure == Nerve cell bodies stained with basophilic dyes will 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. 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 numbers of protein synthesis. The cell body of a neuron is supported by a complex meshwork of structural proteins called neurofilaments, which are assembled into larger neurofibrils. 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). ==Neurons of the brain== The nematode worm (''Caenorhabditis elegans'') has 302 neurons. Scientists have mapped all of the nematode's neurons. The human brain has about 100 billion () neurons and 100 trillion () connections (synapse) between them. ==See also== * F wave * Neuroscience * Artificial neuron * Mirror neuron ==External links == * [http://primate-brain.org High-Resolution Cytoarchitectural Primate Brain Atlases] * [http://purl.net/net/neurowiki NeuroWiki], a wiki website for Neuroscience related topics. * [http://ccdb.ucsd.edu/CCDB/index.shtml Cell Centered Database] UC San Diego images of neurons. Neurons simple:Neuron
The first sentence of this entry used to read "The basic cells of the nervous systems of metazoan animals, whose job is to transmit and process signals." I took the liberty of changing it, suggesting as it did that the job of metazoan animals is to transmit and process signals. (That's a notion of God that's rather different from any I had previously thought of: suppose that there is a God and that s/he created other beings merely to experience things that s/he can not, and then to report on the experience?) ---- From the article: "Synapses of nerves may be between two axons, two dendrites or an axon and a dendrite." Do we have any biologists, physiologists, MD or other specialist who can confirm this statement is correct? My understanding of recent reading I have been pursuing has the axon as an emitter and the dendrite as a collector. Recurrent connections would thus require a portion of the neurons in the nerve fiber or neuron cluster to be oriented roughly 180 degrees. In my current understanding, for the organic circuitry to function as the statement above implies would require multiple neurons in complex patterns rather than individual axon-axon or dendrite-dendrite pairs. User:Mirwin 01:14 Aug 24, 2002 (PDT) :Here is an article that talks about electrical synapses between adjacent dendrites [http://www.jneurosci.org/cgi/content/full/22/8/3227]. I think dendro-dendritic chemcal synaptic connections are fairly rare, but here is an article claiming the existence of dendro-dendritic chemical synapses [http://www.pnas.org/cgi/content/full/98/11/6441]. Chemical synapses between two axons are not unusual; here is a recent article involving such connections [http://www.jneurosci.org/cgi/content/full/23/12/5227]. Some of the important work by Eric Kandel on leraning and memory in Aplysia involves axo-axonic sysapses. See the yellow "facilitating interneurons" making axo-axonic synapses onto the sensory neurone in this diagram [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Search&db=books&doptcmdl=GenBookHL&term=axo-axonic+synapse+AND+161647%5Buid%5D&rid=bnchm.figgrp.3597]. User:68.109.166.14 04:37, 7 Dec 2004 (UTC) ::It is my understanding that all synapses only occur at the tips of dendrites. No - I don't think this is true. There can be different kinds of synapses - for example axonal-dendritic are the obvious ones, but there can also be axonal-somatic, possibly somatic-somatic etc. There is no reason why there can't be multiple synapses on a dendrite, axon or soma. There have been quite a few constraints which various researchers have imagined about neurons and their synapses - most have turned out not to be applicable.User:David Martland Axons function as a conducting line that may go long distances while dendrites branch from end of the axon or directly from the nerve cell body. Electrochemical signals can only go in one direction for each type of neuron (away from the cell body); in sensory neurons signals are sent from sensory receptors (which are modified neurons), in motor cells a signal propagates from the motor cell neuron to effector cells in muscle. The quoted statement doesn't make sense to me. --User:Maveric149 ---- I am concerned at the notion that neurotransmitters are hormones - I will have to check up on this. My gut feeling is that this is incorrect. User:David Martland :The usual definition for a ''hormone'' in human medicine is a substance which is produced in one tissue and carried through the bloodstream to another tissue, where it has its physiological effect. The part that may be getting confused is that some substances (e.g. norepinephrine) are both hormones and neurotransmitters. I think it's probably best not to refer to such substances as hormones when you are discussing them as neurotransmitters. -- User:Someone else 22:13 Nov 19, 2002 (UTC) So shall we remove the reference to hormones then? User:David Martland :Just did. It didn't add anything anyway. -- User:Someone else 22:31 Nov 19, 2002 (UTC)
----
I rearranged things a bit and deleted stuff. The stuff about nerves and the nervous system was up too high given the topic, I thought, and not all of it really germane. Also, I've written long articles on synapses and action potentials, so I felt the paragraphs about those could be pared down. I hope people find these changes agreeable. User:168...
== 100 billions neurons in brains ==
From WordNet:
1. (1) billion, one million million, 1000000000000 -- ((in Britain) the number that is represented as a one followed by 12 zeros)
2. billion, one thousand million, 1000000000 -- ((in the United States) the number that is represented as a one followed by 9 zeros)
Which billion (US or Britain)?
: I have seen 100 billion, United States. There are a large number of small neurons in the cerebellum, and I have seen 100 billion as an estimate of cerebellar neurons. User:68.109.166.14 04:55, 7 Dec 2004 (UTC)
== neural stem cells ==
Anyone heard of these?
They are quite a revolutionary discovery, so....I don't see much mention of them in here. I'm looking for information on it as well. Not to mention the neurons' flexibility in rerouting.
: This textbook might be useful for you [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Search&db=books&doptcmdl=GenBookHL&term=neuronal%5BAll+Fields%5D+AND+stem+cell%5BAll+Fields%5D+AND+neurosci%5Bbook%5D+AND+232053%5Buid%5D&rid=neurosci.section.1748]. Check this out [http://www.pnas.org/cgi/content/full/101/41/14835]. Human neural stem cells [http://www.pnas.org/cgi/content/full/101/9/3202]. User:68.109.166.14 04:55, 7 Dec 2004 (UTC)
From the article:
#The soma, a relatively fat central cell.
I know v. little about biology, but a neuron is a single cell, is it not. The word 'cell' should be replaced (unless the soma ''is'' a seperate cell). User:SgtThroat 22:51, 19 Dec 2004 (UTC)
:I tried to give a better description of the "soma". I'd rather say "neuronal cell body". It is rather disorienting when you follow the link for soma from the neuron page. User:Memenen 01:07, 20 Dec 2004 (UTC)
I've fixed this by adding a stub at soma_(biology), but I don't know what to write there - I'm not a biologist - maybe you could add something? User:SgtThroat 13:13, 21 Dec 2004 (UTC)
== Brain cell regeneration? ==
I've heard a few contradicting statements about whether or not brain cells regenerate over time, so I wondered if anyone would be so kind to give me some clarification on it. Also, if they regenerate - do they regenerate faster than they die, or is the amount of brain cells decreasing all the time? Thanks in advance.
**I think sometimes they can. It depends on the situation. From what I've read, that's a very experimental subject right now. It's also very controversial to try to artificially regernate neurons, because many times the cells used to regenerate neurons are brain stem cells from aborted babies. There is also research to see if hair follicles could be used, which would eliminate the ethical issues. It would be very important if brain cells could regenerate, because so many diseases are a result of destroyed cells that are vital to the brain's existence.
==Welcome!== ''Hi Neuron'', and a Wikipedia:Welcome%2C_newcomers! I hope you have enjoyed editing as much as I did so far and decide to stay. Unfamiliar with the features and workings of Wikipedia? Don't fret! WP:BB! Here's some good links for your reference and that'll get you started in no time!~~~~ . This will automatically add your name and the time after your comments. And finally, if you have any questions or doubts, don't hesitate to contact me on my User_talk:Mailer_diablo. Once again, welcome! =)
- User:Mailer diablo 17:50, 25 Mar 2005 (UTC)
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Neuronotrophic_factor
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#REDIRECT Neuron
Neuron
Neurons (also spelled neurones or called nerve cells) are the primary cell (biology) of the nervous system. In vertebrates, they are found in the brain, the spinal cord and in the nerves and ganglion of the peripheral nervous system. ==Classes== There are three classes of neurons: afferent neurons, efferent neurons, and interneurons. *Afferent neurons convey information from tissues and organs into the central nervous system. *Efferent neurons transmit signals from the central nervous system to the effector cells. *Interneurons connect neurons within the central nervous system. ==Anatomy and histology==
Many highly specialized types of neurons exist, and these differ widely in appearance. Characteristically, neurons are highly asymmetric in shape. Neurons consist of: *The soma_(biology), or cell-body, the relatively large central part of the cell between the dendrites and the axon. *The axon, a much finer, cable-like projection which may extend tens, hundreds, or even tens of thousands of times the diameter of the soma in length. This is the structure which carries nerve signals away from the neuron. Each neuron has only one axon, but this axon may undergo extensive branching and thereby enable communication with many target cells. *The dendrite, a short, branching arbor of cellular extensions. Each neuron has very many dendrites with profuse dendritic branches. These structures form the main information receiving network for the neuron. Axon and dendrites alike are typically only about a micrometre thick, while the soma is usually about 25 micrometres in diameter and not much larger than than the cell nucleus it contains. The axon of a human motoneuron can be over a metre long, reaching from the base of the spine to the toes, while girraffes have single axons running along the whole length of its neck, which is several feet. ==Connectivity== Neurons communicate with one another and to other cells through synapses, where the axon tip of one cell impinges upon a dendrite or soma of another, or less commonly to an axon. Neurons of the cortex in mammals, such as the Purkinje cells, can have over 1000 dendrites each, enabling connections with tens of thousands of other cells. ==Types of signalling== Neurons communicate with one another across synapses. This communication is usually chemically mediated by exocytosis of neurotransmitter molecules. Pre-synaptic neurons (i.e.the neurons which release the neurotransmitter) may produce in the post-synaptic neurons (i.e. the neurons being affected by the neurotransmitter) an electrical stimulation (an ''electrical excitation'') which will spread to the axon hillock generating an ''action potential'' which then travels as a wave of electrical excitation along the axon. Arrival of an action potential at the tip of an axon triggers the release of neurotransmitter at a synapse. Neurotransmitters can either stimulate or suppress (inhibit) the electrical excitability of a target cell. An action potential will only be triggered in the target cell if neurotransmitter molecules acting on their post-synaptic transmembrane receptor cause the cell to reach its threshold potential. Another less common form of communication between neurons is through electrical synapses mediated by gap junctions. ==Adaptations to carrying action potentials== The narrow cross-section of axons and dendrites lessens the metabolic expense of carrying action potentials, although thicker axons convey the impulses more rapidly, generally speaking. Many neurons have insulating sheaths of myelin around their axons. The sheaths are formed by glial cells: oligodendrocytes in the central nervous system and Schwann cells in the peripheral nervous system. The sheath enables the action potentials to travel saltatory conduction than in unmyelinated axons of the same diameter whilst simultaneously preventing short circiuts amoungst intersecting neurons. The myelin sheath in peripheral nerves normally runs along the axon in sections about 1 mm long, punctuated by unsheathed node of Ranvier. Multiple sclerosis is a neurological disorder which results from abnormal demyelination of peripheral nerves. Neurons with demyelinated axons do not conduct electrical signals properly. Neurons and glia make up the two chief cell types of the central nervous system. There are far more glial cells than neurons, and recent experimental results have suggested that glial cells play a vital role in information processing among neurons. == Histology and internal structure == Nerve cell bodies stained with basophilic dyes will 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. 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 numbers of protein synthesis. The cell body of a neuron is supported by a complex meshwork of structural proteins called neurofilaments, which are assembled into larger neurofibrils. 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). ==Neurons of the brain== The nematode worm (''Caenorhabditis elegans'') has 302 neurons. Scientists have mapped all of the nematode's neurons. The human brain has about 100 billion () neurons and 100 trillion () connections (synapse) between them. ==See also== * F wave * Neuroscience * Artificial neuron * Mirror neuron ==External links == * [http://primate-brain.org High-Resolution Cytoarchitectural Primate Brain Atlases] * [http://purl.net/net/neurowiki NeuroWiki], a wiki website for Neuroscience related topics. * [http://ccdb.ucsd.edu/CCDB/index.shtml Cell Centered Database] UC San Diego images of neurons. Neurons simple:Neuron
Neuron
The first sentence of this entry used to read "The basic cells of the nervous systems of metazoan animals, whose job is to transmit and process signals." I took the liberty of changing it, suggesting as it did that the job of metazoan animals is to transmit and process signals. (That's a notion of God that's rather different from any I had previously thought of: suppose that there is a God and that s/he created other beings merely to experience things that s/he can not, and then to report on the experience?) ---- From the article: "Synapses of nerves may be between two axons, two dendrites or an axon and a dendrite." Do we have any biologists, physiologists, MD or other specialist who can confirm this statement is correct? My understanding of recent reading I have been pursuing has the axon as an emitter and the dendrite as a collector. Recurrent connections would thus require a portion of the neurons in the nerve fiber or neuron cluster to be oriented roughly 180 degrees. In my current understanding, for the organic circuitry to function as the statement above implies would require multiple neurons in complex patterns rather than individual axon-axon or dendrite-dendrite pairs. User:Mirwin 01:14 Aug 24, 2002 (PDT) :Here is an article that talks about electrical synapses between adjacent dendrites [http://www.jneurosci.org/cgi/content/full/22/8/3227]. I think dendro-dendritic chemcal synaptic connections are fairly rare, but here is an article claiming the existence of dendro-dendritic chemical synapses [http://www.pnas.org/cgi/content/full/98/11/6441]. Chemical synapses between two axons are not unusual; here is a recent article involving such connections [http://www.jneurosci.org/cgi/content/full/23/12/5227]. Some of the important work by Eric Kandel on leraning and memory in Aplysia involves axo-axonic sysapses. See the yellow "facilitating interneurons" making axo-axonic synapses onto the sensory neurone in this diagram [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Search&db=books&doptcmdl=GenBookHL&term=axo-axonic+synapse+AND+161647%5Buid%5D&rid=bnchm.figgrp.3597]. User:68.109.166.14 04:37, 7 Dec 2004 (UTC) ::It is my understanding that all synapses only occur at the tips of dendrites. No - I don't think this is true. There can be different kinds of synapses - for example axonal-dendritic are the obvious ones, but there can also be axonal-somatic, possibly somatic-somatic etc. There is no reason why there can't be multiple synapses on a dendrite, axon or soma. There have been quite a few constraints which various researchers have imagined about neurons and their synapses - most have turned out not to be applicable.User:David Martland Axons function as a conducting line that may go long distances while dendrites branch from end of the axon or directly from the nerve cell body. Electrochemical signals can only go in one direction for each type of neuron (away from the cell body); in sensory neurons signals are sent from sensory receptors (which are modified neurons), in motor cells a signal propagates from the motor cell neuron to effector cells in muscle. The quoted statement doesn't make sense to me. --User:Maveric149 ---- I am concerned at the notion that neurotransmitters are hormones - I will have to check up on this. My gut feeling is that this is incorrect. User:David Martland :The usual definition for a ''hormone'' in human medicine is a substance which is produced in one tissue and carried through the bloodstream to another tissue, where it has its physiological effect. The part that may be getting confused is that some substances (e.g. norepinephrine) are both hormones and neurotransmitters. I think it's probably best not to refer to such substances as hormones when you are discussing them as neurotransmitters. -- User:Someone else 22:13 Nov 19, 2002 (UTC) So shall we remove the reference to hormones then? User:David Martland :Just did. It didn't add anything anyway
Neuron
==Welcome!== ''Hi Neuron'', and a Wikipedia:Welcome%2C_newcomers! I hope you have enjoyed editing as much as I did so far and decide to stay. Unfamiliar with the features and workings of Wikipedia? Don't fret! WP:BB! Here's some good links for your reference and that'll get you started in no time!
Most Wikipedians would prefer to just work on articles of their own interest. But if you have some free time to spare, here are some Template:Opentask that you may want to help out :
- Wikipedia:Tutorial, learn to have fun with Wikipedia.
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Neuron
Neuron
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Neuronopathy
Neuronotrophic_factor
Neurons
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Neurontin
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