White matter
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| White matter | |
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| The formation of the spinal nerve from the dorsal and ventral roots. (White matter labeled at right.) | |
| Latin | substantia alba |
| Dorlands/Elsevier | s_27/12766685 |
White matter is one of the two main solid components of the central nervous system.
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[edit] Structure
It is composed of myelinated nerve cell processes, or axons, which connect various grey matter areas (the locations of nerve cell bodies) of the brain to each other and carry nerve impulses between neurons.
Cerebral and spinal white matter do not contain dendrites, which can only be found in grey matter along with neural cell bodies and shorter axons.
[edit] Function
Generally, white matter can be understood as the parts of the brain and spinal cord responsible for information transmission (axons); whereas, grey matter is mainly responsible for information processing (neuron bodies).
[edit] 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") 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.
[edit] 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.
- So-called "Type 1 astrocytes" had a fibroblast appearance and resided in both grey matter and white matter.
- "Type 2 astrocytes" has a neuron-like appearance and resided in white matter alone (Sherman, Chris).
[edit] Clinical relevance
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 grey matter regeneration is less likely.
[edit] Notes
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