Question

Which of the following best describes the effect of sympathetic activity on ventricular contractile cells?

A) the rates of contraction and relaxation both increase, whereas the force of contraction decreases
B) the rate of contraction and the force of contraction both increase, whereas the rate of relaxation decreases
C) the rates of contraction and relaxation and the force of contraction all increase
D) the rates of contraction and relaxation both decrease, whereas the force of contraction increases
E) the force of contraction increases, whereas the rates of contraction and relaxation are not affected

Answer 1

Sympathetic activity increases the rate and force of contraction in ventricular contractile cells. Hence, B) is correct.

Step-by-step explanation:

Sympathetic stimulation increases the rate of contraction and the force of contraction in ventricular contractile cells. It triggers the release of norepinephrine (NE) from the cardiac nerves and stimulates the adrenal cortex to secrete epinephrine and NE.

NE binds to both alpha and beta receptors on the cardiac muscle cell membrane, increasing metabolic rate and the force of contraction. As a result, sympathetic activity increases stroke volume and decreases residual end-systolic volume in the ventricles.