Human heart has a specialized conductive system, through which impulses from SA node are transmitted to all other parts of the heart.
Conductive System In Human Heart:
Conductive system of the heart is formed by the modified cardiac muscle fibers. These fibers are the specialized cells, which conduct the impulses rapidly from SA node to the ventricles, Conductive tissues of the heart are also called the junctional tissues.
Components of Conductive System In Human Heart:
- AV Node
- Bundle of His
- Right and left bundle branches
- Purkinje fibers
SA node is situated in right atrium, just below the opening of superior vena cava. AV node is situated in right posterior portion of intra-atrial septum. Impulses from SA node are conducted throughout right and left atria. Impulses also reach the AV node via some specialized fibers called internodal fibers. There are three types of internodal fibers:
- Anterior internodal fibers of Bachman
- Middle internodal fibers of Wenckebach
- Posterior internodal fibers of Thorel
All these fibers from SA node converge on AV node and interdigitate with fibers of AV node. From AV node, the bundle of His arises. It divides into right and left branches, which run on either side of the interventricular septum. From each branch of bundle of His, many Purkinje fibers arise and spread all over the ventricular myocardium.
Velocity Of Impulses At Different Parts Of Conductive System:
- Atrial Muscle Fibers : 0.3 meter/second
- Internodal Fibers : 1.0 meter/second
- AV Node : 0.05 meter/second
- Bundle of His : 0.12 meter/second
- Purkinje Fibers : 4.0 meter/second
- Ventricular Muscle Fibers : 0.5 meter/second
Thus, the velocity of impulses is maximum in Purkinje fibers and minimum at AV node.