The ANS sympathetic stimulation has what general effect on heart rate and contractility?

• A. Decreases HR and increases contractility
• B. No effect
• C. Increases heart rate and increases contractility
• D. Increases HR and decreases contractility

Answer: (C)

Sympathetic stimulation raises both how fast the heart beats and how forcefully it contracts. When nerves release norepinephrine onto beta-1 receptors in the SA node, it speeds up the rate of spontaneous depolarization, increasing heart rate. In the ventricular myocardium, beta-1 stimulation boosts cAMP and activates PKA, which enhances calcium entry through L-type channels and increases calcium release from the intracellular stores. More calcium available for each heartbeat strengthens the interaction of actin and myosin, producing a stronger (positive inotropic) contraction. This same pathway also enhances calcium cycling for quicker relaxation, preparing the heart for the next beat. In short, sympathetic activity makes the heart beat faster and with greater force.