Which structure regulates rhythmic contractions of the heart?

The structure that regulates the rhythmic contractions of the heart is the SA node, or sinoatrial node. This specialized group of cells is located in the right atrium of the heart and functions as the primary pacemaker. The SA node generates electrical impulses that initiate each heartbeat, setting the timing for the contraction of the heart muscles.

When the cells in the SA node depolarize, they create an action potential that spreads throughout the heart. This process triggers the atria to contract and pushes blood into the ventricles. The impulses then travel to the atrioventricular node and subsequently through the bundle of His and Purkinje fibers, but the pacing of the heartbeat originates in the SA node. Its inherent rhythmicity ensures that the heart contracts consistently and maintains optimal blood flow throughout the body, even in the absence of external nervous stimulation.