CAMRT Radiography Practice Exam

Which structure of the heart initiates the electrical impulse?

1. Atrioventricular node

2. Sinoatrial node

3. Bundle of His

4. Purkinje fibers

The correct answer is: Sinoatrial node

The sinoatrial (SA) node is often referred to as the heart's natural pacemaker. This small cluster of cells is located in the right atrium and has the unique ability to generate electrical impulses spontaneously. These impulses are crucial for the initiation and regulation of the heart's rhythm, as they spread through the atria, prompting them to contract and push blood into the ventricles. The SA node sets the pace for the entire heart by determining the heart rate under normal physiological conditions. This ability to initiate electrical impulses distinguishes it from other components of the heart's conduction system, such as the atrioventricular (AV) node, Bundle of His, and Purkinje fibers, which primarily serve to propagate the impulses generated by the SA node. The AV node acts as a gatekeeper, slowing the electrical signal before transmitting it to the ventricles, while the Bundle of His and Purkinje fibers conduct impulses throughout the ventricles to ensure coordinated contraction. Understanding the role of the SA node is fundamental to grasping how the heart maintains a regulated and effective pumping action, which is critical for overall circulatory function.