Question

Visceral smooth muscle differs from skeletal muscle in that 

A. It contracts when stretched. 

B. It is not paralyzed when its motor nerve supply is cut. 

C. Its cells have unstable resting membrane potentials. 

D. It contains no actin or myosin. 

E. Excitation depends more on influx of extracellular calcium than release of calcium from endoplasmic reticulum.

Answer 1

A. True The intrinsic ‘myogenic’ response in smooth muscle opposes stretch; skeletal muscle requires a nerve reflex arc for this type of response. 

B. True It continues to contract due to local pacemakers. 

C. True They show spontaneous depolarization between contractions. 

D. False In smooth muscle, actin and myosin filaments occur but are less obvious on microscopy. 

E. True Smooth muscle has a less well-developed sarcoplasmic reticulum.