Efferent Nerve Fiber

also centrifugal, or motor, nerve fiber, the nerve cell outgrowth, or axon, that together with its membrane transmits excitation from the central nervous system to such organs as the muscles and glands. Efferent nerve fibers differ in kind—for example, they may be cranial or spinal. They may belong to the somatic or the autonomic division of the nervous system. Of the peripheral nerves, only a few are genuinely efferent; most of them are mixed—that is, they include afferent, or centripetal, nerve fibers. A single nerve may contain efferent fibers that lead to different organs.

The efferent nerve fibers are divided into three main groups— A, B, and C—and several subgroups according to the rate of excitation conductivity. Group A consists of the fibers that have the highest rate of conductivity and innervate the skeletal muscles. The parasympathetic and sympathetic fibers, which have a slower rate of conductivity, belong to groups B and C.