Final answer:
The atrioventricular (AV) node is a cluster of myocardial cells in the right atrium crucial for heart rhythm regulation by delaying the electrical impulse from the SA node before it is transmitted to the ventricles via the atrioventricular bundle.
Step-by-step explanation:
The atrioventricular (AV) node is a second clump of specialized myocardial conductive cells, located in the inferior portion of the right atrium within the atrioventricular septum. This essential component of the heart's electrical conduction system plays a critical role by ensuring that there is a delay before the impulse, which originates at the SA node, is transmitted to the ventricles.
The atrioventricular septum acts as a barrier, preventing the impulse from directly spreading to the ventricles. The small diameter of the cells within the AV node and less efficient conduction between nodal cells contribute to this delay. It takes roughly 100 milliseconds for the impulse to pass through the AV node, which is crucial for synchronized heart function, allowing the atria to complete their contraction and effectively pump blood into the ventricles. The atrioventricular bundle, or bundle of His, then receives the impulse from the AV node and transmits it through the interventricular septum to the rest of the ventricles.