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nerve ending[′nərv ‚end·iŋ]
a specialized structure in the terminal portion of the long outgrowth, or axon, of a nerve cell. At the site of the nerve ending, the axon does not have a myelin sheath.
Sensory nerve endings receive information, while effector nerve endings transmit information. A nerve impulse travels along the axon away from the sensory nerve ending, where it originates. In contrast, a nerve impulse travels toward an effector ending. A sensory nerve ending is structurally and functionally similar to a dendrite, and like a dendrite it has a receptor membrane. Sensory nerve endings can be independent or connected to special sensory cells.
An effector nerve ending, usually appearing as a local widening at the very end or in the middle of an axon, contains mitochondria and masses of secretory vesicles or granules that secrete mediators into the extracellular space. The terminal brush of an axon in the midbrain of a rat has an overall length of more than 0.5 m and contains about half a million nerve endings. The effector nerve endings of many autonomic neurons in the sympathetic ganglia are contained in the terminal brushes; these brushes intertwine to form complex terminal plexuses. Autonomic nerve endings are structurally similar to effector nerve endings.