What effect does parasympathetic innervation have on heart rate?

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Study for the Cardiovascular System Test. Learn about heart anatomy, function, and circulatory pathways with flashcards and multiple-choice questions. Each question provides detailed explanations. Get prepared for your exam!

Multiple Choice

What effect does parasympathetic innervation have on heart rate?

Explanation:
Parasympathetic innervation slows the heart. Nerves of the vagus release acetylcholine onto the pacemaker cells in the sinoatrial (and to some extent the AV) node. Acetylcholine binds to muscarinic M2 receptors, activating pathways that increase potassium conductance. This hyperpolarizes the pacemaker cells and slows the rate of spontaneous depolarization (the slope of phase 4), reducing the firing rate of the SA node. It also slows conduction through the AV node. The net effect is a slower heart rate, opposed by sympathetic input which increases rate.

Parasympathetic innervation slows the heart. Nerves of the vagus release acetylcholine onto the pacemaker cells in the sinoatrial (and to some extent the AV) node. Acetylcholine binds to muscarinic M2 receptors, activating pathways that increase potassium conductance. This hyperpolarizes the pacemaker cells and slows the rate of spontaneous depolarization (the slope of phase 4), reducing the firing rate of the SA node. It also slows conduction through the AV node. The net effect is a slower heart rate, opposed by sympathetic input which increases rate.

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