The nurse is reviewing the sequence of the cardiac cycle. The nurse recognizes that the electrical stimulus of the cardiac cycle follows which sequence?
A.
AV node-SA node bundle of His bundle branches
B.
SA node- AV node-bundle of His bundle branches
C.
Bundle of His AV node SA node- Erb’s Point
D.
AV node-SA node-bundle of His- Erb’s Point
The Correct Answer and Explanation is:
The correct answer is B. SA node – AV node – bundle of His – bundle branches.
Explanation:
The cardiac cycle is regulated by a specialized electrical conduction system that ensures the heart beats in a coordinated manner. Understanding the sequence of the electrical stimulus is crucial for comprehending how the heart maintains rhythm and pumps blood efficiently.
- SA Node (Sinoatrial Node): The sequence begins with the SA node, which is located in the right atrium near the opening of the superior vena cava. Often referred to as the heart’s natural pacemaker, the SA node generates electrical impulses that initiate each heartbeat. These impulses cause the atria to contract and push blood into the ventricles.
- AV Node (Atrioventricular Node): The electrical impulse then travels to the AV node, located at the junction between the atria and ventricles, near the lower part of the interatrial septum. The AV node serves as a critical gatekeeper; it delays the electrical impulse slightly before transmitting it to the ventricles. This delay is essential because it allows the ventricles enough time to fill with blood from the atria before they contract.
- Bundle of His (Atrioventricular Bundle): After the AV node, the impulse moves to the Bundle of His, which is a pathway that transmits the electrical signal from the AV node to the ventricles. This bundle divides into the left and right bundle branches.
- Bundle Branches: The impulse travels down the left and right bundle branches, which extend through the interventricular septum toward the apex of the heart. These branches are responsible for conducting the electrical impulse to the respective ventricles.
- Purkinje Fibers: Finally, the electrical impulse reaches the Purkinje fibers, which spread throughout the ventricles. The Purkinje fibers ensure that the ventricles contract in a coordinated manner, starting from the apex and moving upward to push blood out of the heart into the pulmonary artery and aorta.
This sequence—SA node, AV node, Bundle of His, and Bundle Branches—is crucial for the synchronized contraction of the heart. Disruption in any part of this pathway can lead to arrhythmias and affect the heart’s ability to pump blood effectively. Understanding this sequence helps in diagnosing and treating various cardiac conditions and ensures effective management of heart rhythm disorders.