GENERAL HISTOLOGY

Detailed explanation-1: -When made to contract, the smooth muscle cells shorten, thereby propelling the luminal contents of the organ, or the cell shortening varies the diameter of a tube to regulate the flow of its contents. There are also bundles of smooth muscle cells attached to the hairs of the skin and to the iris and lens of the eye.

Detailed explanation-2: -If a muscle fiber is stimulated so rapidly that it does not relax at all between stimuli, a smooth, sustained contraction called tetanus occurs (illustrated by the straight line in c above & in the diagram below).