What is Smooth Muscle?

Smooth muscle provides the contractile force for movement in internal organs under control of the involuntary or autonomic nervous system. Smooth muscle is responsible for movement of the bolus through the digestive tract, the flow of blood through blood vessels, and the emptying of urine from the urinary bladder, except for the external sphincter.

Smooth muscle is composed of long spindle-shaped cells, each with a single nucleus. Smooth muscle tissue is usually arranged in sheets, with the cells in electrical contact with one another through structures called gap junctions. Gap junctions are involved in propagating an action potential generated in the membrane of one smooth muscle cell to all the other muscle cells in the sheet of tissue. The extent of contraction depends upon how much the cell is depolarized.