Conducting System of the Heart
Conducting System of the Heart is composed of modified, specialized cardiac muscle cells that lie immediately beneath the endocardium and carry impulses throughout the cardiac muscle, signaling the heart chambers to contract in the proper sequence.
1. Sinoatrial Node
- Is a small mass of specialized cardiac muscle fibers that lies in the myocardium at the upper end of the crista terminalis near the opening of the SVC in the right atrium.
- Is known as the pacemaker of the heart and initiates the heartbeat, which can be altered by autonomic nervous stimulation (sympathetic stimulation speeds it up, and vagal stimulation slows it down). Impulses spread in a wave along the cardiac muscle fibers of the atria and also travel along an internodal pathway to the AV node.
- Is supplied by the sinus node artery, which is a branch of the right coronary artery.
2. AV Node
- Lies in the interatrial septum, superior and medial to the opening of the coronary sinus in the right atrium, receives the impulse from the sinoatrial (SA) node and passes it to the AV bundle.
- Is supplied by the AV nodal artery, which usually arises from the right coronary artery opposite the origin of the posterior interventricular artery.
- Is innervated by autonomic nerve fi bers, although the cardiac muscle fi bers lack motor endings.
3. AV Bundle (Bundle of His)
- Begins at the AV node and runs along the membranous part of the interventricular septum.
- Splits into right and left branches, which descend into the muscular part of the interventricular septum, and breaks up into terminal conducting fi bers (Purkinje fibers) to spread out into the ventricular walls.