Which autonomic influence increases the heart rate and force of contraction?

Which autonomic influence increases the heart rate and force of contraction?

• A. Sympathetic innervation
• B. Parasympathetic innervation
• C. Hormonal influence only
• D. Local valve reflexes

Answer: (A)

The main idea is how autonomous nerves modulate heart activity. Sympathetic innervation speeds both the heart’s rhythm and its squeezing power. Nerve endings release norepinephrine that activates beta-1 receptors on the SA node and myocardium. This raises cAMP levels, which boosts the rate of depolarization in the SA node (faster heart rate) and increases calcium availability in heart muscle cells (stronger contraction). The result is a higher heart rate and greater contractile force, boosting cardiac output. Parasympathetic input, in contrast, lowers heart rate by acting on muscarinic receptors and has only a modest effect on ventricular contraction. Hormonal influences (like adrenaline) can mimic sympathetic effects, but the question targets autonomic innervation, where sympathetic input best fits. Local valve reflexes don’t regulate heart rate or force of contraction.

The main idea is how autonomous nerves modulate heart activity. Sympathetic innervation speeds both the heart’s rhythm and its squeezing power. Nerve endings release norepinephrine that activates beta-1 receptors on the SA node and myocardium. This raises cAMP levels, which boosts the rate of depolarization in the SA node (faster heart rate) and increases calcium availability in heart muscle cells (stronger contraction). The result is a higher heart rate and greater contractile force, boosting cardiac output.

Parasympathetic input, in contrast, lowers heart rate by acting on muscarinic receptors and has only a modest effect on ventricular contraction. Hormonal influences (like adrenaline) can mimic sympathetic effects, but the question targets autonomic innervation, where sympathetic input best fits. Local valve reflexes don’t regulate heart rate or force of contraction.