Nerve Fiber, Vasomotor

a nerve fiber that transmits impulses from the central nervous system to the smooth musculature of blood vessels. Vasomotor nerve fibers cause the musculature to contract or relax, resulting in the constriction or dilatation of blood vessels. By regulating the width of blood vessels, the fibers help to maintain arterial blood pressure at a constant level and to redistribute blood in the body (the influx of blood to effectors and the weakening of the blood flow in the vessels of inactive organs). Vasomotor nerve fibers were first described in 1842 by the Russian anatomist and physiologist A. P. Val’ter.

Vasomotor nerve fibers may be vasoconstrictive or vasodila-tive. Vasoconstrictive fibers are very important in the regulation of blood circulation. Usually part of the sympathetic nervous system, they innervate the blood vessels of the skin, mucous membranes, lungs, meninges, and abdominal organs, causing the vessels to constrict. The transection of these fibers causes the vessels to dilate. Vasoconstrictive nerve impulses to the coronary blood vessels are transmitted by fibers of the parasympathetic vagus nerve. Vasodilative fibers, which are concentrated in the glossopharyngeal (chorda tympani), lingual, and pelvic nerves, belong to the parasympathetic nervous system; the vasodilative fibers that innervate the vessels of the skeletal muscles and heart belong to the sympathetic nervous system. The functions of both types of fibers have not been completely established. Their corresponding vessels dilate more when stimulated than when vasoconstrictive influences cease. The impairment of normal vascular innervation results in a variety of functional disorders.