Smooth muscle that exhibits rhythmical contraction in the absence of external stimuli also necessarily exhibits which of the following?
ExplanationAn intrinsic rhythmical “pacemaker” is necessary for a muscle to contract spontaneously and rhythmically. Intestinal smooth muscle, for example, exhibits a rhythmical slow-wave potential that transiently depolarizes and repolarizes the muscle membrane. This slow-wave does not stimulate contraction itself, but if the amplitude is sufficient, it can trigger one or more action potentials that result in Ca++ influx and contraction. A high resting cytosolic Ca++ concentration would support a sustained contraction, and hyperpolarization would favor relaxation.
