nervous system [L, nervus, nerve; Gk, system] , the extensive, intricate network of structures that activates, coordinates, and controls all the functions of the body. It is divided into the central nervous system, composed of the brain and the spinal cord, and the peripheral nervous system, which includes the cranial nerves and the spinal nerves. These morphological subdivisions combine and communicate to innervate the somatic and visceral parts of the body with the afferent and efferent nerve fibers. Afferent fibers carry sensory impulses to the central nervous system. Efferent fibers carry motor impulses from the central nervous system to the muscles and other organs. The somatic fibers are associated with the bones, muscles, and skin. The visceral fibers are associated with the internal organs, blood vessels, and mucous membranes. Compare autonomic nervous system. See also Color Atlas of Human Anatomy, pp. A23-A27.
