By Michael Weiss. âSectarian violence in Syria raises fears,â screamed the headline of a Washington Post article on the murder Tuesday of 16 Syrians in the city of Homs, which lies 100 miles north of Damascus.
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.
Smooth muscle is fundamentally different from skeletal muscle and cardiac muscle in terms of structure, function, regulation of contraction, and excitation-contraction coupling. Smooth muscle cells known as myocytes, have a fusiform shape and, like striated muscle, can tense and relax.