Question

Write and explain cardiac conduction system?

Answer 1

Cardiac conduction system:

• The conducting system is made up of myocardium that is specialized for initiation and conduction of the cardiac impulse.The conducting system has the following parts.

•Sinuatrial node or SA node: It is known as the pacemaker of the heart.It generates impulses at the rate of about 70-100 beats/min and initiates the heartbeat.It is horse-shoe shaped and is situated at the atriocaval junction in the upper part of the sulcus terminals.The impulse travels through the atrial wall and reaches the AV node.

•Atrioventricular node or AV node: It is smaller than the SA node and situated in the lower and dorsal part of the atrial septum just above the opening of the coronary sinus.It generates impulses at a rate of about 40-60 beats/min.

•Atrioventricular bundle or AV bundle: It is the only muscular connection between atrial and ventricular musculatures.  It begins as the AV node crosses the AV ring and descends along the posteroinferior border of the membranous part of the ventricular septum.At the upper part of the muscular septum,it divides into right and left branches.

•The right branch of AV bundle passes down the right side of the interventricular septum.A large part enters the moderator band to reach the anterior wall of the right ventricle where it divides into purkinje fibres.

•The left branch of AV bundle descends on the left side of the interventricular septum and is distributed to the left ventricle after dividing into purkinje fibres.

•The Purkinje fibres form a subendocardial plexus.They are large pale fibres striated only at their margins.They usually possess double nuclei.These generate impulses at the rate of 20-35 beats/min.