What is the first step in the sequence of impulses through the heart?

The sequence of impulses through the heart begins with the sinoatrial (SA) node, which is often referred to as the heart's natural pacemaker. The SA node generates electrical impulses that initiate the heartbeat and set the rhythm for the entire heart, stimulating the atria to contract and pump blood into the ventricles. This is the crucial first step in the heart's electrical conduction system.

Following the activation of the SA node, the electrical impulse travels to the atrioventricular (AV) node, then to the Bundle of His, and subsequently spreads through the Purkinje fibers. While all these components are essential for the coordinated contraction of the heart, it is the SA node that starts the entire process. Without the SA node’s initial impulse, the subsequent conduction would not occur, highlighting its critical role in maintaining heart rhythm and function.