an important difference between single-unit and multiunit smooth muscle is the
Multi-unit smooth muscle is found in the walls of large blood vessels, in large airways in the lungs, in the muscle of the eye that adjusts the lens and alters the size of the pupil, and in the base of hair follicles in the skin. SINGLE-UNIT muscle is the more common. It is commonly called visceral muscle and is found in the walls of hollow organs (e.g. digestive, reproductive, urinary system). Sheets of single-unit muscle fibres contract as a single unit as they are electrically linked by gap junctions (like cardiac muscle). This permits coordinated contraction of a whole organ. Single unit smooth muscle is self-excitable as clusters of specialised smooth muscle cells display spontaneous electrical activity.