Anatomy and Physiology II Practice Test

The sinoatrial (SA) node is the part of the heart's electrical conduction system responsible for initiating the heartbeat. It serves as the natural pacemaker of the heart, generating electrical impulses that trigger contractions in the atria, leading to the pumping action of the heart. Located in the right atrium, the SA node sends regular electrical signals that cause the atrial muscles to contract and push blood into the ventricles. This rhythmic activation is essential for maintaining a consistent heart rate and ensuring effective blood circulation throughout the body.

In the context of the other components of the conduction system, while the atrioventricular (AV) node plays a critical role in delaying the impulse from the atria before it reaches the ventricles, it does not initiate the heartbeat. The Bundle of His and Purkinje fibers are involved in transmitting the electrical impulses through the ventricles to coordinate their contraction, but they also do not have the capability to start the heartbeat independently like the SA node does.

Therefore, the SA node is central to the heart's electrical activity, setting the pace that governs the overall heart rhythm.