White matter
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2008-07-03T14:47:24Z
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/* Types of astrocytes */
{{Infobox Anatomy |
Name = White matter |
Latin = substantia alba |
GraySubject = |
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Image = spinal nerve.svg |
Caption = The formation of the spinal nerve from the dorsal and ventral roots. (White matter labeled at right.) |
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DorlandsPre = s_27 |
DorlandsSuf = 12766685 |
}}
'''White matter''' is one of the three main solid components of the [[central nervous system]] designated by color. The other two are [[gray matter]] and [[substantia nigra]].
==Structure==
White matter is composed of [[myelin]]ated [[neuron|nerve cell]] processes, or [[axon]]s, which connect various gray matter areas (the locations of nerve cell bodies) of the [[brain]] to each other, and carry [[nerve impulse]]s between neurons.
[[Cerebrum|Cerebral]]- and spinal white matter do not contain [[dendrite]]s, which can only be found in [[gray matter]] along with [[Soma (biology)|neural cell bodies]], and shorter axons.{{Fact|date=May 2008}}
==Function==
The white matter is the tissue through which messages pass between different areas of gray matter within the nervous system. Using a computer network as an analogy, the gray matter can be thought of as the actual computers themselves, whereas the white matter represents the network cables connecting the computers together. The white matter is white because of the fatty substance (myelin) that surrounds the nerve fibers (axons). This myelin is found in almost all long nerve fibers, and acts as an electrical insulation. This is important because it allows the messages to pass quickly from place to place.
The brain in general (and especially a child's brain) can adapt to white-matter damage by finding alternative routes that bypass the damaged white-matter areas, and can therefore maintain good connections between the various areas of gray matter.
Unlike gray matter, which peaks in development in a person's twenties, the white matter continues to develop, and peaks in late middle age.{{Fact|date=April 2008}}
==Location==
White matter forms the bulk of the deep parts of the brain and the superficial parts of the [[spinal cord]]. Aggregates of [[grey matter]] such as the [[basal ganglia]] ([[caudate nucleus]], [[putamen]], [[globus pallidus]], [[subthalamic nucleus]], [[nucleus accumbens]]) and brain stem nuclei ([[red nucleus]], [[substantia nigra]], [[cranial nerve]] nuclei) are spread within the cerebral white matter.
The [[cerebellum]] is structured in a similar manner as the cerebrum, with a superficial mantle of cerebellar cortex, deep cerebellar white matter (called the "[[arbor vitae (anatomy)|arbor vitae]]") and aggregates of grey matter surrounded by deep cerebellar white matter ([[dentate nucleus]], [[globose nucleus]], [[emboliform nucleus]], and [[fastigial nucleus]]). The fluid-filled [[ventricular system|cerebral ventricles]] (lateral ventricles, [[third ventricle]], [[Mesencephalic duct|cerebral aqueduct]], [[fourth ventricle]]) are also located deep within the cerebral white matter.
==Types of astrocytes==
In 1983, M. C. Raff et al. discovered that tissue samples originating from rat optic nerve contained two morphologically distinct types of [[astrocytes]]s.
* So-called "Type 1 astrocytes" had a [[fibroblasts]] appearance and resided in both gray matter and white matter.
* "Type 2 astrocytes" has a neuron-like appearance and resided in white matter alone (Sherman, Chris).
==Clinical relevance==
[[Multiple Sclerosis]] (MS) is one of the most common disease which affects white matter. In MS lesions, the [[myelin]] shield around the [[axons]] has been destroyed by [[inflammation]].
Changes in white matter known as [[amyloid]] plaques are associated with [[Alzheimer's disease]] and other neurodegenerative diseases. White matter injuries ("axonal shearing") may be reversible, while gray matter regeneration is less likely.
In November 2007, the Toronto based Centre for Addiction and Mental Health published a study in the [[Journal of Psychiatry Research]] showing that child molesters with pedophilia suffer from a "significant lack of white matter connecting six different areas of the brain all known to play a role in sexual arousal."<ref>[http://news.bbc.co.uk/2/hi/health/7116506.stm Brain wiring link to paedophilia]</ref><ref>[http://www.cbc.ca/story/health/national/2007/11/28/pedophiles-study.html Pedophiles have less brain white matter: Toronto study]</ref>
The study of white matter has been advanced with the [[neuroimaging]] technique called [[diffusion tensor imaging]] where [[magnetic resonance imaging]] (MRI) brain scanners are used.
As of 2007, more than 700 publications have been published.<ref>{{Cite journal
| title = Diffusion Tensor Imaging (DTI)-based White Matter Mapping in Brain Research: A Review
| author = Yaniv Assaf, Ofer Pasternak
| doi = 10.1007/s12031-007-0029-0
| year = 2008
| volume = 34
| issue = 1
| pages = 51–61
| journal = Journal of Molecular Neuroscience
}}</ref>
==Notes==
<references/>
== External links ==
* [http://www.dtiatlas.org White Matter Atlas]
* {{eMedicineDictionary|White+matter}}
{{Nervous tissue}}
{{Spinal cord}}
[[Category:Central nervous system]]
[[Category:Neuroanatomy]]
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