View source for White matter

{{Infobox Anatomy |
  Name         = {{PAGENAME}} |
  Latin        = substantia alba |
  GraySubject  = |
  GrayPage     = |
  Image        = spinal nerve.svg |
  Caption      = The formation of the spinal nerve from the dorsal and ventral roots. (White matter labeled at right.) |
  Image2       = |
  Caption2     = |
  System       = |
  MeshName     = |
  MeshNumber   = |
  DorlandsPre  = s_27 |
  DorlandsSuf  = 12766685  |
}}


==Overview==
'''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==
It 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.

==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 as the insulation is important for allowing 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 which bypass the damaged areas of white matter and can therefore maintain good connections between the various areas of gray matter.

Unlike gray matter, which peaks in development in a persons twenties, the white matter continues to develop and peaks in late middle age.

==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.and suppl

==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 [[astrocyte]]s. 
* So-called "Type 1 astrocytes" had a [[fibroblast]] 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==

Leukoaraiosis is "non-specific white matter changes in the brain, often seen after age 65".<ref name=MeSH">Leukoaraiosis. Available at https://www.ncbi.nlm.nih.gov/mesh/?term=Leukoaraiosis</ref> The prevalence of these changes is 20% among patients over age 60.<ref name="pmid12660385">{{cite journal| author=Vermeer SE, Prins ND, den Heijer T, Hofman A, Koudstaal PJ, Breteler MM| title=Silent brain infarcts and the risk of dementia and cognitive decline. | journal=N Engl J Med | year= 2003 | volume= 348 | issue= 13 | pages= 1215-22 | pmid=12660385 | doi=10.1056/NEJMoa022066 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=12660385  }} </ref> These lesions are associated with a doubling of risk of dementia<ref name="pmid12660385"/><ref name="pmid20660506">{{cite journal| author=Debette S, Markus HS| title=The clinical importance of white matter hyperintensities on brain magnetic resonance imaging: systematic review and meta-analysis. | journal=BMJ | year= 2010 | volume= 341 | issue=  | pages= c3666 | pmid=20660506 | doi=10.1136/bmj.c3666 | pmc=2910261 | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=20660506  }}  [https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=21266598 Review in: Evid Based Ment Health. 2011 Feb;14(1):1] </ref>, stroke<ref name="pmid20660506"/>, and death<ref name="pmid20660506"/>.

<ref name="pmid19470964">{{cite journal| author=Putaala J, Kurkinen M, Tarvos V, Salonen O, Kaste M, Tatlisumak T| title=Silent brain infarcts and leukoaraiosis in young adults with first-ever ischemic stroke. | journal=Neurology | year= 2009 | volume= 72 | issue= 21 | pages= 1823-9 | pmid=19470964 | doi=10.1212/WNL.0b013e3181a711df | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=19470964  }} </ref>

[[Multiple Sclerosis]] 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.

==Notes==
<references/>

{{neuroanatomy-stub}}

== 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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