Explain the roles of the sinoatrial node, the atrioventricular node and the Purkyne tissue in the cardiac cycle (knowledge of nervous and hormonal control is not expected)

Sourav PanOctober 30, 2024

Answered

The sinoatrial node (SAN), atrioventricular node (AVN), and Purkyne tissue (also called Purkinje fibers) are key structures in the heart that coordinate and regulate the cardiac cycle, ensuring the heart beats in a synchronized manner to pump blood efficiently.

1. Sinoatrial Node (SAN)

• The SAN, located in the upper wall of the right atrium, is often called the pacemaker of the heart. It initiates the electrical impulses that start each heartbeat.
• The SAN generates electrical signals (action potentials) at regular intervals, which cause the atria to contract. This contraction pushes blood from the atria into the ventricles.
• Since the SAN sets the rhythm of these impulses, it determines the heart rate and ensures that the atria contract before the ventricles.

2. Atrioventricular Node (AVN)

• The AVN is located in the lower part of the right atrium, near the septum that separates the atria from the ventricles.
• The AVN acts as a relay point for the electrical impulses coming from the SAN. It introduces a slight delay before passing the signal to the ventricles. This delay is crucial because it allows time for the atria to finish contracting and for the ventricles to fill with blood before they contract.
• By timing the impulses between atrial and ventricular contractions, the AVN helps coordinate the sequential contraction of the heart chambers, ensuring efficient blood flow from the atria to the ventricles.

3. Purkyne Tissue (Purkinje Fibers)

• Purkyne tissue consists of specialized conducting fibers located in the walls of the ventricles, forming part of the bundle of His, which branches into the left and right bundles within the septum.
• After the AVN transmits the impulse, the signal travels rapidly down the bundle of His to the Purkyne fibers, which spread throughout the walls of the ventricles.
• These fibers distribute the electrical impulse quickly to the ventricular muscle, causing simultaneous contraction of the ventricles from the bottom (apex) upward. This coordinated contraction pushes blood out of the heart efficiently—into the pulmonary artery from the right ventricle and into the aorta from the left ventricle.