National Academy of Sports Medicine (NASM) Group Fitness Instructor Practice Exam

What portion of the heart originates the electrical impulse that initiates the contraction of the heart muscle, and is also considered the pacemaker of the heart?

1. Ventricles

2. Atrioventricular node

3. Sinoatrial node

4. Bundle of His

The correct answer is: Sinoatrial node

The sinoatrial node, often referred to as the SA node, is the correct answer as it serves as the primary pacemaker of the heart. Located in the right atrium, the SA node generates electrical impulses that dictate the heart rate and rhythm. By initiating the contraction of the heart muscle, it effectively coordinates the heart's pumping action and ensures that the atria contract before the ventricles, promoting efficient blood flow through the heart. The other options present structures that play important roles in the electrical conduction system of the heart but do not initiate the electrical impulse. For instance, the atrioventricular node receives impulses from the SA node and serves as a gateway to the ventricles, but it does not generate the heart's intrinsic rhythm. The ventricles are the main pumping chambers of the heart, and they contract in response to the electrical signals but do not initiate those signals themselves. The Bundle of His transmits electrical impulses from the AV node to the ventricles, playing a crucial part in the conduction pathway but also lacks the role of primary pacemaker. Thus, the SA node's unique function as the originator of electrical impulses is what makes it the correct answer.