What are the conducting components of the heart?

The heart has four conducting components – Sinoatrial Node, Atrioventricular Node, Atrioventricular Bundle, and Purkinje Fibers. These are specialized structures responsible for generating and transmitting electrical impulses that regulate the heartbeat. 

Sinoatrial (SA) Node 

The sinoatrial node is a collection of specialized cells that serve as the intrinsic pacemaker of the heart, regulating heart rate. Also known as pacemaker cells, the SA node spontaneously generates electrical impulses, which are transmitted through both the left and right atria, causing the atrial myocardium to contract. 

The SA node is located in the upper wall of the right atrium in close proximity to its junction with the superior vena cava.  

Atrioventricular (AV) Node 

Located in the atrioventricular septum of the heart between the right atrium and the left ventricle, the atrioventricular node is a group of specialized cells that act as a relay station. On receiving electrical impulses from the atria, the AV node delays the impulses briefly, allowing the ventricles adequate time to fill with blood before contracting. It then transmits the wave of excitation into the atrioventricular bundle. 

Atrioventricular Bundle (Bundle of His)

After passing through the AV node, the electrical impulse travels down the atrioventricular bundle. Also known as the Bundle of His, the atrioventricular bundle is a bundle of cardiac muscle cells specialized for electrical conduction. They serve to transmit electrical impulses from the AV node to the left and right ventricles. 

The atrioventricular bundle runs down the membranous part of the interventricular septum separating the two ventricles, before dividing into two branches – one entering the left ventricle and the other entering the right ventricle. On entering the ventricles, each branch terminates as multiple Purkinje fibers. 

Purkinje Fibers

The Purkinje fibers are a network of glycogen-rich cells with extensive gap junctions. They are located in the subendocardial surface of the ventricular walls. The Purkinje fibers rapidly transmit the electrical impulse to the ventricular myocardium, resulting in coordinated and synchronized ventricular contraction, wherein the blood is passed from the right and left ventricles to the pulmonary artery and aorta respectively.

The four conducting components of the heart work together to ensure that the electrical signals in the heart are generated and transmitted in a specific sequence, leading to the coordinated contraction of the atria and ventricles, which is essential for effective pumping of blood throughout the body.