Pilomotor Nerve Fibers

fibers of the sympathetic division of the autonomic nervous system that innervate the arrectores pilorum muscles, which are the smooth muscles that cause hairs to stand erect. Preganglionic pilomotor nerve fibers arise in the cells of the lateral horns of the spinal cord and proceed to the ganglia of the sympathetic trunk. The postganglionic fibers that leave the sympathetic trunk reach their assigned segment of the skin as part of a spinal nerve. Pilomotor nerve fibers mediate the pilomotor reflex, a contraction of the hair muscles of the skin that raises the hairs and causes gooseflesh in response to a variety of stimuli, for example, cold. Two kinds of pilomotor reflex are distinguished, cerebral and spinal. The cerebral pilomotor reflex, which is normal, occurs in healthy persons, for example, when the back of the neck is stimulated; the spinal pilomotor reflex accompanies some diseases of the spinal cord that disrupt the spinal cord’s connection with the brain.