Which neurotransmitter slows heart rate?

Which neurotransmitter slows heart rate?

• A. Acetylcholine
• B. Norepinephrine
• C. Epinephrine
• D. Dopamine

Answer: (A)

The main idea is parasympathetic control of the heart. Acetylcholine slows heart rate by being released from the vagus nerve onto the SA and AV nodes. It binds to M2 muscarinic receptors, which activates a Gi protein pathway that reduces cAMP. This lowers the activity of the heart’s pacemaker channels (funny channels) and calcium channels, slowing the rate of spontaneous depolarization and reducing conduction velocity. The result is a slower heart rate. In contrast, norepinephrine and epinephrine stimulate beta-1 receptors to increase cAMP, speeding up pacemaker activity and conduction, which raises heart rate. Dopamine can also raise heart rate at higher doses, so it doesn’t produce the slowing effect. Acetylcholine is the neurotransmitter that slows the heart.

The main idea is parasympathetic control of the heart. Acetylcholine slows heart rate by being released from the vagus nerve onto the SA and AV nodes. It binds to M2 muscarinic receptors, which activates a Gi protein pathway that reduces cAMP. This lowers the activity of the heart’s pacemaker channels (funny channels) and calcium channels, slowing the rate of spontaneous depolarization and reducing conduction velocity. The result is a slower heart rate.

In contrast, norepinephrine and epinephrine stimulate beta-1 receptors to increase cAMP, speeding up pacemaker activity and conduction, which raises heart rate. Dopamine can also raise heart rate at higher doses, so it doesn’t produce the slowing effect. Acetylcholine is the neurotransmitter that slows the heart.