Nervous System Terminology

The following terms are commonly used in descriptions of nervous system features:

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  • A nerve fiber is an axon or dendrite. A nerve is a bundle of nerve fibers in the PNS. A nerve tract is a bundle of nerve fibers in the CNS.

  • White matter consists of myelinated axons of neurons in the CNS.

  • Gray matter consists of unmyelinated portions of neurons (cell bodies, dendrites, and axon terminals), unmyelinated neurons, and neuroglia in the CNS.

  • Nuclei are clusters of cell bodies in the CNS. Ganglia are clusters of cell bodies in the PNS (except the basal ganglia, which are more appropriately called basal nuclei).

  • Vesicles are fluid-filled cavities in the brain that form during early development. The tissues that form the vesicles divide to become the various components of the brain.

  • Ventricles are interconnected cavities in the mature brain that originate from the fluid-filled vesicles. Circulating fluid (cerebrospinal fluid—CSF) in the ventricles provides nourishment for nervous tissue and transports waste away from the nervous tissue.

  • Peduncles are large tracts that emerge from certain regions of the brain. Their large size gives the appearance of supporting the structure from which they emerge (peduncle means “little foot”).

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