al is elicited anywhere within the muscle mass, it generally travels in all directions in the muscle. Multi-unit smooth muscle is made up of individual units without interconnecting bridges. Smooth muscle, unlike other types of muscles, contracts when stretched in the absence of any extrinsic innervation. Stretch is followed by a decline in membrane potential, an increase in the frequency of spikes and a general increase in tone.
             Smooth muscle is a nonstriated involuntary type of muscle found in the stomach, intestines, bladder, and uterus and in the walls of most arteries and veins. Its activity is controlled by the autonomic nervous system, but all smooth muscle do not respond in the same manner to the same stimulus. For example, sympathetic stimulation produces a decrease in the rhythmic contractility of smooth muscle in the gut, but causes the circular smooth muscle of the arteries to contract and constrict the vessels. Parasympathetic stimulation evokes an increase in intestinal contractility, but has little effect on arterial smooth muscle. Another unique property of smooth muscle is its ability to maintain approximately the same amount of tone and rhythmic contractility at different degrees of stretch (Tharp).
             The smooth muscle in the tract is excited by almost continual slow, intrinsic electrical activity along the membranes of the muscle fibers. This activity has 2 basic types of electrical waves:
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