ocr: sinu-artial node bundle of His - à e atrioventricular E - node Purkinje system The impulse for the activation of the heart muscle myocardium) is normally propagated in a rapid and orderly fashion. This begins with depolarization in the sinu-atrial (SA) node, and then spreads to the atria. ropagation continues in the atrio- ventricular (AV) node where there is a brief delay. The AV node in turn activates the oundle of His which divides into branches and finally into the Purkinje fibers. The impulse for depolar- ization is conducted rapidly to the inner ayer of the ventricle muscle.