Cardiac Conduction System

Normal Conduction System

Function
1. To generate rhythmical impulses.
2. To conduct the impulses throughout the myocardium.

Normal Conductive Tissue
Specialized muscle tissue that is not or poorly contractile.
Sinus node (SA Node) –pacemaker of the heart.
Internodal pathways–conductive tissue from SA node through atrial muscle.
Bachman’s bundle–interatrial internodal pathway–communicates with the right and left atria.
Junctional tissues:
Atrioventricular Node (AV node)–bridge to the ventricles–slows impulse transmission to ventricle.

HIS bundle
Right and left bundle branches (left bundle subdivides in two–left anterior bundle and left posterior bundle).
Purkinje fibers (Highest velocity of conduction system)

Cardiac Muscle
Striated-like typical skeletal muscle.
Contain contractile proteins actin-myosin.
Extensive sarcoplasmic reticulum (more than skeletal muscle)–storage for calcium.
Intercalated discs–cell membranes that separate ends of individual cells–low impedance to electrical conductivity.
Heart functions as a syncytium–one stimulus causes entire mass of heart to function as one unit.
Automaticity–ability of cell to spontaneously reach threshold potential and depolarize. (Pacer cells)
Excitability–ability of cell to respond to a stimulus (muscle cells).