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