Which structure initiates the electrical impulse in the heart?

The sinoatrial (SA) node is recognized as the primary pacemaker of the heart and is crucial for the initiation of the electrical impulse that triggers heartbeats. This small cluster of cells is located in the right atrium and is responsible for generating electrical signals that propagate through the heart's conduction system, leading to coordinated contractions of the atria and ventricles.

The SA node's specific role in setting the rhythm of the heart is vital for maintaining the proper sequence of cardiac contractions and ensuring effective blood circulation. When the SA node fires an impulse, it travels through the atria, causing them to contract and push blood into the ventricles. This electrical activity then reaches the atrioventricular (AV) node, which serves to relay the impulse to the ventricles but does not initiate it.

Other structures like the Bundle of His and Purkinje fibers have important roles in conducting and coordinating the electrical impulses but do not start the impulses themselves. The Bundle of His carries impulses from the AV node to the ventricles, while Purkinje fibers distribute the impulses throughout the ventricular myocardium, leading to contraction. Therefore, with the SA node's role in initiating the beat, it is correctly identified as the structure that starts the electrical impulse in