Final answer:
The atrioventricular (AV) node is a critical part of the heart's electrical system that delays the impulse from the SA node before transmitting it to the ventricles, ensuring the proper timing of heart muscle contractions during the cardiac cycle.
Step-by-step explanation:
The atrioventricular (AV) node is a key component of the heart's electrical conduction system which plays a crucial role in coordinating the timing of heart muscle contractions. It is a cluster of specialized myocardial conductive cells located in the inferior part of the right atrium within the atrioventricular septum.
The AV node receives the impulse from the sinoatrial (SA) node, then facilitates a critical pause before transmitting the impulse to the atrioventricular bundle.
The delayed transmission through the AV node is significant because it ensures the atria have adequate time to contract and pump blood into the ventricles before the ventricles contract themselves. This delay, which takes approximately 100 milliseconds, is caused by factors such as the small diameter of the AV node cells and less efficient conduction between them compared to other conducting cells.
In a healthy young individual, the AV node can manage a maximal transmission rate of 220 impulses per minute, setting the upper limit of heart rate. Conditions such as heart damage or stimulation from drugs can lead to higher heart rates but can reduce the effectiveness of the heart's blood-pumping ability.
During the cardiac cycle, specifically in cardiac diastole, all chambers of the heart are relaxed and blood flows freely into the heart. The SA node initiates the impulse which travels through the atria via internodal pathways consisting of anterior, middle, and posterior bands before reaching the AV node.
The specialized internodal pathways transmit the impulse from the SA node throughout the atrial myocardial contractile cells and to the AV node, which then continues the process of cardiac rhythm.