smooth muscle [AS, smoth] , one of three kinds of muscle, composed of elongated, spindle-shaped cells in muscles not under voluntary control, such as the smooth muscle of the intestines, stomach, and other viscera. The nucleated cells of smooth muscle are arranged parallel to one another and to the long axis of the muscle they form. Smooth muscle fibers are shorter than striated muscle fibers, have only one nucleus per fiber, and are smooth in appearance. Biofeedback devices may help many people gain partial control of contractions of involuntary smooth muscles. Also called involuntary muscle, unstriated muscle. Compare cardiac muscle, striated muscle.
