Biology – The heart | e-Consult

The sinoatrial node (SAN) is the heart's natural pacemaker. Its primary function is to initiate the electrical impulses that trigger the cardiac cycle. The SAN spontaneously depolarizes, generating an electrical signal that spreads throughout the atria, causing them to contract. This ensures that atrial contraction occurs in a coordinated and timely manner.

The atrioventricular node (AVN) receives the electrical impulse from the atria and delays it before transmitting it to the ventricles. This delay is crucial for several reasons:

• Atrial Emptying: It allows the atria to fully contract and empty their contents into the ventricles before ventricular contraction begins. This ensures maximum ventricular filling.
• Coordination: It provides a coordinated sequence of atrial and ventricular contractions. Without the delay, the atria and ventricles might contract asynchronously, reducing the efficiency of blood flow.
• Ventricular Filling: The delay gives the ventricles time to fill with blood from the atria, ensuring they have sufficient blood volume for effective ejection.

Without the AVN's function, the atria and ventricles would contract simultaneously, leading to a significant reduction in cardiac output and impaired blood circulation. The delay ensures that the ventricles are adequately filled before they contract, maximizing the efficiency of blood ejection.