What effect does the sympathetic innervation have on the heart?

What effect does the sympathetic innervation have on the heart?

• A. Increases heart rate, contractile force, and coronary vessel dilation.
• B. Decreases heart rate.
• C. Reduces myocardial contractility.
• D. Constricts coronary vessels.

Answer: (A)

Sympathetic activation prepares the heart for increased workload. When the sympathetic nerves release norepinephrine, it mainly acts on beta-1 adrenergic receptors in the SA node, AV node, and myocardium. This speeds up the pacemaker rate, enhances conduction, and increases the force of each beat. At the same time, agonist action on receptors in the coronary arteries promotes vasodilation, boosting blood flow to meet the higher needs of the exercising heart. So the net effect is a faster heart rate, stronger contractions, and greater coronary perfusion. In contrast, slowing the heart rate or reducing contractility are effects of parasympathetic activity, and constricting the coronary vessels would limit blood flow rather than increase it, which is not the typical sympathetic response.

Sympathetic activation prepares the heart for increased workload. When the sympathetic nerves release norepinephrine, it mainly acts on beta-1 adrenergic receptors in the SA node, AV node, and myocardium. This speeds up the pacemaker rate, enhances conduction, and increases the force of each beat. At the same time, agonist action on receptors in the coronary arteries promotes vasodilation, boosting blood flow to meet the higher needs of the exercising heart. So the net effect is a faster heart rate, stronger contractions, and greater coronary perfusion.

In contrast, slowing the heart rate or reducing contractility are effects of parasympathetic activity, and constricting the coronary vessels would limit blood flow rather than increase it, which is not the typical sympathetic response.