White matter: Encyclopedia - White matter

White matter

White matter is one of the two main solid components of the central nervous system.

It 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.

White matter is composed of nerve cell processes, or axons, which connect various grey matter areas of the brain to each other and carry nerve impulses between neurons. Cerebral and spinal white matter does not contain dendrites, which can only be found in grey matter along with neural cell bodies and shorter axons.

White matter is distinguished in that it is composed of axonal nerve fibers, covered by a myelin sheath. Grey matter is composed primarily of nerve cell bodies. Generally, white matter can be understood as the parts of the brain and spinal cord responsible for information transmission; whereas, grey matter is mainly responsible for information processing. White matter injuries ("axonal shearing") may be reversible, while grey matter regeneration is less likely.

Adapted from the Wikipedia article "White matter", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki