White matter
White matter | |
---|---|
Details | |
Location | Central nervous system |
Identifiers | |
Latin | substantia alba |
MeSH | D066127 |
TA98 | A14.1.00.009 A14.1.02.024 A14.1.02.201 A14.1.04.101 A14.1.05.102 A14.1.05.302 A14.1.06.201 |
TA2 | 5366 |
FMA | 83929 |
Anatomical terminology |
White matter refers to areas of the central nervous system (CNS) that are mainly made up of myelinated axons, also called tracts.[1] Long thought to be passive tissue, white matter affects learning and brain functions, modulating the distribution of action potentials, acting as a relay and coordinating communication between different brain regions.[2]
White matter is named for its relatively light appearance resulting from the
Structure
White matter
White matter is composed of bundles, which connect various
The total number of long range fibers within a cerebral hemisphere is 2% of the total number of cortico-cortical fibers (across cortical areas) and is roughly the same number as those that communicate between the two hemispheres in the brain's largest white tissue structure, the corpus callosum.[4] Schüz and Braitenberg note "As a rough rule, the number of fibres of a certain range of lengths is inversely proportional to their length."[4]
The proportion of blood vessels in the white matter in nonelderly adults is 1.7–3.6%.[5]
Grey matter
The other main component of the brain is grey matter (actually pinkish tan due to blood capillaries), which is composed of neurons. The substantia nigra is a third colored component found in the brain that appears darker due to higher levels of melanin in dopaminergic neurons than its nearby areas. Note that white matter can sometimes appear darker than grey matter on a microscope slide because of the type of stain used. Cerebral and spinal white matter do not contain dendrites, neural cell bodies, or shorter axons,[citation needed] which can only be found in grey matter.
Location
White matter forms the bulk of the deep parts of the brain and the superficial parts of the
The
Myelinated axon length
Men have more white matter than women both in volume and in length of myelinated axons. At the age of 20, the total length of myelinated fibers in men is 176,000 km while that of a woman is 149,000 km.[6] There is a decline in total length with age of about 10% each decade such that a man at 80 years of age has 97,200 km and a woman 82,000 km.[6] Most of this reduction is due to the loss of thinner fibers. However, this study only included 36 participants.[6]
Function
White matter is the tissue through which messages pass between different areas of grey matter within the central nervous system. 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.
Unlike grey matter, which peaks in development in a person's twenties, the white matter continues to develop, and peaks in middle age.[7]
Research
Amyloid plaques in white matter may be associated with Alzheimer's disease and other neurodegenerative diseases.[10] Other changes that commonly occur with age include the development of leukoaraiosis, which is a rarefaction of the white matter that can be correlated with a variety of conditions, including loss of myelin pallor, axonal loss, and diminished restrictive function of the blood–brain barrier.[11]
There is also evidence that substance abuse may damage white matter microstructure, though prolonged abstinence may in certain cases reverse such white matter changes.[12]
Volume
Smaller volumes (in terms of group averages) of white matter might be associated with larger deficits in
Imaging
The study of white matter has been advanced with the
A 2009 paper by Jan Scholz and colleagues[21] used diffusion tensor imaging (DTI) to demonstrate changes in white matter volume as a result of learning a new motor task (e.g. juggling). The study is important as the first paper to correlate motor learning with white matter changes. Previously, many researchers had considered this type of learning to be exclusively mediated by dendrites, which are not present in white matter. The authors suggest that electrical activity in axons may regulate myelination in axons. Or, gross changes in the diameter or packing density of the axon might cause the change.[22][self-published source?] A more recent DTI study by Sampaio-Baptista and colleagues reported changes in white matter with motor learning along with increases in myelination.[23]
See also
- White matter dissection
- Ventriculomegaly
- Vascular dementia
- Vanishing white matter disease
- Brain atrophy
References
- ISBN 978-0878936137.
Areas of the CNS made up mainly of myelinated axons are called white matter.
- .
- ^ Klein, S.B., & Thorne, B.M. Biological Psychology. Worth Publishers: New York. 2007.[ISBN missing][page needed]
- ^ ISBN 978-0-415-27723-5.
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Given that our the central nervous system is an intricately balanced, complex network of billions of neurons and supporting cells, some might imagine that extrinsic substances could cause irreversible brain damage. Our review paints a less gloomy picture of the substances reviewed, however. Following prolonged abstinence, abusers of alcohol (Pfefferbaum et al., 2014) or opiates (Wang et al., 2011) have white matter microstructure that is not significantly different from non-users. There was also no evidence that the white matter microstructural changes observed in longitudinal studies of cannabis, nicotine, or cocaine were completely irreparable. It is therefore possible that, at least to some degree, abstinence can reverse effects of substance abuse on white matter. The ability of white matter to "bounce back" very likely depends on the level and duration of abuse, as well as the substance being abused.
- PMID 24041523.
- PMID 10978049.
- OCLC 903956524.
- ^ PMID 18538868.
- ^ ISBN 978-0-12-411469-2.
- PMID 25142557.
- PMID 25325459.
- S2CID 3354176.
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- ^ "White Matter Matters". Dolan DNA Learning Center. Archived from the original on 2009-11-12. Retrieved 2009-10-19.[self-published source]
- PMID 24336716.
Further reading
- Fields, R. D. (2010). "Change in the Brain's White Matter: The role of the brain's white matter in active learning and memory may be underestimated". Science. 330 (6005): 768–769. PMID 21051624.
External links
- Media related to White matter at Wikimedia Commons