Complete the Concept Map to describe ionic movement during action potentials in cardiac pacemaker and contractile cells, and trace the conduction pathway. Drag the appropriate labels to their respective targets. AV nodes, bundles, branches, and Purkinje fibers -are specifically made of → directly trigger atria to contract and activate Ca2+ ions directly trigger ventricles to contract and activate cardiac muscle fibers enter plateau phase due to slow influx of K ions rapidly depolarize due to influx of Na ions pacemaker cells -repolarize due to efflux of → slowly depolarize due to influx of SA nodes