Vertebrate Smooth Muscle

Abstract

Muscles of inner organs of vertebrates, such as gut, uterus, bronchial tree and blood vessels, are termed “smooth muscles” as they lack ordinary striations. Smooth muscles may be spontaneously active, or they may contract in response to nervous or hormonal stimulation. For example, think of the constriction of blood vessels that may be influenced by sympathetic nerves releasing noradrenahne as a transmitter. Hormones and neurotransmitters exert their action on the smooth muscle cell by reacting with specific targets on the cell membrane, the receptors, but they may or may not alter the membrane potential. The question of how these membrane events are coupled to the contractile responses has been one of the most intriguing problems in smooth muscle research in recent years.