- White matter
Name = White matter
Latin = substantia alba
Caption = The formation of the spinal nerve from the dorsal and ventral roots. (White matter labeled at right.)
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White matter is one of the three main solid components of the
central nervous system. White matter tissue of the freshly cut brain appears white to the naked eye because of being composed largely of lipid. The other two components of the brain are gray matterand substantia nigra.
White matter is composed of bundles of
myelinated nerve cell processes (or axons), which connect various gray matter areas (the locations of nerve cell bodies) of the brainto each other, and carry nerve impulses between neurons.
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
White matter forms the bulk of the deep parts of the brain and the superficial parts of the
spinal cord. Aggregates of grey mattersuch as the basal ganglia( caudate nucleus, putamen, globus pallidus, subthalamic nucleus, nucleus accumbens) and brain stem nuclei ( red nucleus, substantia nigra, cranial nervenuclei) are spread within the cerebral white matter.
cerebellumis structured in a similar manner as the cerebrum, with a superficial mantle of cerebellar cortex, deep cerebellar white matter (called the "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 cerebral ventricles (lateral ventricles, third ventricle, cerebral aqueduct, fourth ventricle) are also located deep within the cerebral white matter.
Types of astrocytes
In 1983, M. C. Raff et al. [cite journal |author=Raff MC, Abney ER, Cohen J, Lindsay R, Noble M |title=Two types of astrocytes in cultures of developing rat white matter: differences in morphology, surface gangliosides, and growth characteristics |journal=J. Neurosci. |volume=3 |issue=6 |pages=1289–1300 |year=1983 |month=June |pmid=6343560 |doi= |url=http://www.jneurosci.org/cgi/pmidlookup?view=long&pmid=6343560] discovered that tissue samples originating from rat optic nerve contained two morphologically distinct types of
* So-called "Type 1 astrocytes" had a
fibroblastsappearance 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).
Multiple Sclerosis(MS) is one of the most common disease which affects white matter. In MS lesions, the myelinshield around the axonshas been destroyed by inflammation.
Changes in white matter known as
amyloidplaques are associated with Alzheimer's diseaseand 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 Researchshowing 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." [ [http://news.bbc.co.uk/2/hi/health/7116506.stm Brain wiring link to paedophilia] ] [ [http://www.cbc.ca/story/health/national/2007/11/28/pedophiles-study.html Pedophiles have less brain white matter: Toronto study] ]
The study of white matter has been advanced with the
neuroimagingtechnique called diffusion tensor imagingwhere magnetic resonance imaging(MRI) brain scanners are used.As of 2007, more than 700 publications have been published. [cite journal |author=Assaf Y, Pasternak O |title=Diffusion tensor imaging (DTI)-based white matter mapping in brain research: a review |journal=J. Mol. Neurosci. |volume=34 |issue=1 |pages=51–61 |year=2008 |pmid=18157658 |doi=10.1007/s12031-007-0029-0 |url=]
* [http://www.dtiatlas.org White Matter Atlas]
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