CONDUCTION SYSTEM OF THE HEART
The rhythmic contractile process originates spontaneously in the conducting system and travels to different regions of the heart.The conduction system consists of specialised cardiac muscle present in the sino atrial node., the Atrio ventricular node, the Atrio ventricular bundle and its right and left terminal branches and the subendocardial plexus of Purkinjee fibres
SINOATRIAL NODE: The SA node is located in the wall of the RA in the upper part of the Sulcus terminalis just to the right of opening of the SVC. The node spontaneously gives origin to rhythmical electrical impulse that spread in all directions through the cardiac muscle of the atria and cause the muscle to contract.
ATRIO VENTRICULAR NODE: The AV node is placed on the lower art of the atrial septum just above the attachment of the septal cusp of tricuspid valve. From it, the cardiac impulse is conducted to the ventricles by the AV bundle. The speed of conduction of impulse through the AV node is 0.11s
ATRIO VENTRICULAR BUNDLE: The AV bundle or bundle of HIS is the only pathway of cardiac muscle that connects the myocardium of atria and ventricles. The bundle descends through the fibrous skeleton of the heart. The AV bundle descends behind the septal cusp of the tricuspid valve to reach the inferior border of the membranous part of the ventricular septum. At the upper border of the muscular part of the septum it divides into two branches, one for each ventricle. The Right bundle branch (RBB) passes down the right side of ventricular septum to reach the moderator band, where it crosses to the anterior wall of RV. Here it becomes continuous with the fibres of purkinjee plexus. The Left bundle branch (LBB) pierces the septum into two branches (anterior and posterior), which eventually become continuous with the fibres of the purkinjee plexus.
INTERNODAL CONDUCTION PATHS: Impulse from the SA node have been shown to travel to the AV node more rapidly than they can travel by passing along the ordinary myocardium. This phenomenon has been explained by the description of special pathways in the atrial wall, having a structure consisting of mixture of purkinjee fibres and ordinary cardiac muscle cells. The pathways are
>Anterior internodal pathways
Middle internodal pathways
Posterior internodal pathways