ABSTRACT
About 100 mseconds after the pacemaker ‘fires’ impulses traveling through special conducting fibers, the atrial muscles themselves stimulate a second area
of nodal tissue, the atrioventricular node. From here, impulses are carried by special muscle fibers (in the bundle of His which branches and ends as Purkinje fibers emerge) to the walls of the right and left ventricles which then contract almost simultaneously. Although the fibers in the bundle of His conduct impulses very speedily, the atrioventricular node has slow-acting fibers: thus a delay is imposed between atrial and ventricular contractions, allowing time for ventricular filling.
