What is the function of the vagus nerve in heart innervation?

What is the function of the vagus nerve in heart innervation?

• A. It increases heart rate by signaling SA node and AV node.
• B. It triggers ventricular contraction directly.
• C. It decreases heart rate by signaling SA node and AV node.
• D. It blocks conduction through the Purkinje system.

Answer: (C)

The vagus nerve provides parasympathetic control to the heart, mainly slowing the rhythm by acting on the nodal tissue. It releases acetylcholine onto M2 receptors in the SA and AV nodes, which makes these cells less likely to fire and slows conduction through the AV node. This produces a decrease in heart rate (negative chronotropy) and a slower conduction velocity (negative dromotropy). The vagus has little direct effect on the ventricular muscle, so it does not trigger ventricular contraction.

The vagus nerve provides parasympathetic control to the heart, mainly slowing the rhythm by acting on the nodal tissue. It releases acetylcholine onto M2 receptors in the SA and AV nodes, which makes these cells less likely to fire and slows conduction through the AV node. This produces a decrease in heart rate (negative chronotropy) and a slower conduction velocity (negative dromotropy). The vagus has little direct effect on the ventricular muscle, so it does not trigger ventricular contraction.