Smooth muscle cell

Smooth muscle does not have actin and myosin arranged into arrays like stirated muscle so appears uniformed under a microscope when stained. A smooth muscle cell is located within the walls of tubular or hollow organs or vessels for structural support. It is involved in physiologically substantial processes within the body including: regulation of blood flow through the vascular system; movement of the iris and expulsive actions of the urinary bladder and the uterus during childbirth. Smooth muscle cells have an elongated spindle shaped cell with a single nuclei.

Smooth muscle contracts using the sliding filament mechanism, where actin and myosin slide over each other. This mechanism requires energy which is provided by the hydrolysis of ATP. The globular heads that protrude from the myosin molecule bind to the actin filament which forms crossbridges. The myosin moves along the actin and then releases from the actin (also requiring the use of ATP). Contraction is initiated by calcium-regulated phosphorylation of myosin.