Intrinsic Conduction System of the Heart
Step 1: Stimulation of the sinoatrial node
Remember that the SA node has the fastest rate of depolarization, and thus sets the rhythm of the heart. This is known as the “pacemaker” of the heart with its sinus rhythm.
Typically, the rate of impulses is 75 per minute; the SA node has the fastest rate of depolarization in the heart.
Step 2: Stimulation of the atrioventricular node
The depolarization wave spreads through the atria in the internodal pathway. Propagation occurs through gap junctions. Impulses are delayed for 0.1 s to allow the atria to contract prior to the ventricles. The 0.1 s pause is also attributable to the smaller diameter of the fibers in the AV node.
Step 3: Propagation to the AV bundle
Atria and ventricles are not connected by gap junctions, and this bundle is the only electrical connection between the atria and the ventricles.
Step 4: Splitting into the bundle branches
These branches propogate along the interventricular septum towards the apex of the heart.
Step 5: Propagation up the Purkinje fibers (subendocardial conducting network)
The Purkinje fibers propogate superiorly to the walls of the ventricles from the apex of the heart. These impulses travel through the means of gap junctions.
AP wave of intrinsic conduction system
Remember, these graphs are plotted against time; they reveal relative speeds of depolarization in the intrinsic conduction system.
Copyright: 2016 Pearson Education