Which nervous system is responsible for controlling bradycardia?

The correct choice is the parasympathetic nervous system, which plays a key role in controlling heart rate, particularly in inducing bradycardia. Bradycardia is defined as a slower than normal heart rate, generally below 60 beats per minute in adults. The parasympathetic nervous system, through the vagus nerve, releases acetylcholine, which acts on the heart's pacemaker cells to reduce heart rate.

In contrast, the sympathetic nervous system typically responds to stress or increased activity by increasing heart rate. The central nervous system integrates signals from both the sympathetic and parasympathetic systems but does not directly control heart rate on its own. The peripheral nervous system acts as a network that communicates between the central nervous system and the rest of the body; although it includes both the sympathetic and parasympathetic branches, it is not specifically responsible for bradycardia alone. Thus, the parasympathetic nervous system is the primary player in the mechanism that leads to a decrease in heart rate, resulting in bradycardia.