central nervous system

central nervous system: see nervous system.

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central nervous system

the mass of nerve tissue that controls and coordinates the activities of an animal. In vertebrates it consists of the brain and spinal cord

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central nervous system [′sen·trəl ′nər·vəs ‚sis·təm]

(neuroscience)

The division of the vertebrate nervous system comprising the brain and spinal cord.

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Central nervous system

That portion of the nervous system composed of the brain and spinal cord. The brain is enclosed in the skull, and the spinal cord within the spinal canal of the vertebral column. The brain and spinal cord are intimately covered by membranes called meninges and bathed in an extracellular fluid called cerebrospinal fluid. Approximately 90% of the cells of the central nervous system are glial cells which support, both physically and metabolically, the other cells, which are the nerve cells or neurons.

Functionally similar groups of neurons are clustered together in so-called nuclei of the central nervous system. When groups of neurons are organized in layers (called laminae) on the outer surface of the brain, the group is called a cortex, such as the cerebral cortex and cerebellar cortex. The long processes (axons) of neurons course in the central nervous system in functional groups called tracts. Since many of the axons have a layer of shiny fat (myelin) surrounding them, they appear white and are called the white matter of the central nervous system. The nuclei and cortex of the central nervous system have little myelin in them, appear gray, and are called the gray matter of the central nervous system. See Brain, Nervous system (vertebrate)