Describe the structure and function of smooth muscle, commenting on the type and source of nervous stimulation smooth muscle receives.
The cells of smooth muscle, which forms the walls of many internal organs as well as the walls of arteries and veins, have one nucleus each and lack striation. The individual cells or fibers of smooth muscle are long, thin, and pointed at their ends. The fibers are often interwoven to form sheets instead of bundles as in striated muscle. Smooth muscle is stimulated by the autonomic nervous system. Each cell is excited by two nerve fibers: One nerve fiber transmits impulses that elicit contraction while the other transmits impulses that inhibit contraction. Smooth muscle is also able to contract without nervous stimulation as in the peristaltic movement of the intestine tract, for example. Smooth muscle carries out adjustments to an organism's internal environment.
