MUSCLE PHYSIOLOGY

Detailed explanation-1: -Smooth muscles are of two types. They are: Single-unit (visceral) smooth muscle: All the cells function collectively and simultaneously as a single unit (unitary). Multiunit smooth muscle: It is a type of muscle in which all the cells cannot function collectively and work independently.

Detailed explanation-2: -Smooth muscle relaxation occurs either as a result of removal of the contractile stimulus or by the direct action of a substance that stimulates inhibition of the contractile mechanism. Regardless, the process of relaxation requires a decreased intracellular Ca2+ concentration and increased MLC phosphatase activity.

Detailed explanation-3: -One single action potential leading to an increased intracellular Ca2+ from sarcoplasmic reticulum release produces a single muscle contraction known as a twitch. Because the action potential duration is shorter than the twitch duration, the muscle fiber may be activated again before muscle relaxation occurs.

Detailed explanation-4: -Layers of smooth muscle cells line the walls of various organs and tubes in the body, and the contractile function of smooth muscle is not under voluntary control. Contractile activity in smooth muscle is initiated by a Ca(2+)-calmodulin interaction to stimulate phosphorylation of the light chain of myosin.