Which system slows the heart rate?

• A. Sympathetic nervous system
• B. Central nervous system
• C. Parasympathetic nervous system
• D. Somatic nervous system

Answer: (C)

Slowing the heart rate happens when the parasympathetic branch of the autonomic nervous system takes the control. It releases acetylcholine onto the heart’s pacemaker cells, especially at the SA and AV nodes, which lowers how often they fire and thus reduces heart rate.

In contrast, the sympathetic branch does the opposite, increasing heart rate and the force of contraction. The central nervous system coordinates these signals but doesn’t directly slow the heart by itself. The somatic nervous system governs voluntary movements and isn’t involved in changing heart rate.