Which branch of the autonomic nervous system slows heart rate and reduces conduction velocity?

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Multiple Choice

Which branch of the autonomic nervous system slows heart rate and reduces conduction velocity?

Parasympathetic input via the vagus nerve slows heart rate and reduces conduction velocity. It does this mainly through acetylcholine acting on M2 receptors in the SA and AV nodes. The signal decreases cAMP and increases potassium conductance, hyperpolarizing pacemaker cells and lowering the slope of phase 4 depolarization. This slows the rate of impulse generation and, in the AV node, slows conduction, which lengthens the time between atrial and ventricular activation. In contrast, the sympathetic system speeds things up: norepinephrine via beta-1 receptors increases cAMP, boosting pacemaker currents and conduction. The enteric and somatic systems aren’t involved in setting heart rhythm. So the branch that slows heart rate and reduces conduction velocity is the parasympathetic nervous system (vagal tone).

Parasympathetic input via the vagus nerve slows heart rate and reduces conduction velocity. It does this mainly through acetylcholine acting on M2 receptors in the SA and AV nodes. The signal decreases cAMP and increases potassium conductance, hyperpolarizing pacemaker cells and lowering the slope of phase 4 depolarization. This slows the rate of impulse generation and, in the AV node, slows conduction, which lengthens the time between atrial and ventricular activation.

In contrast, the sympathetic system speeds things up: norepinephrine via beta-1 receptors increases cAMP, boosting pacemaker currents and conduction. The enteric and somatic systems aren’t involved in setting heart rhythm. So the branch that slows heart rate and reduces conduction velocity is the parasympathetic nervous system (vagal tone).

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