Final answer:
The papillary muscles are not a population of pacemaker cells in the heart; rather, they contribute to the mechanical function of heart valves. The SA node, AV node, and Purkinje fibers make up the heart's electrical conduction system responsible for initiating and coordinating contractions.
Step-by-step explanation:
The papillary muscles are NOT a population of pacemaker cells in the heart. The heart's pacemaking system consists of the sinoatrial (SA) node, atrioventricular (AV) node, and the Purkinje fiber system. These pacemaker cells and structures are responsible for generating and propagating the electrical signals that coordinate the heart's beating. The SA node, located near the wall of the right atrium, spontaneously initiates the electrical charges that make the atria contract.
These impulses then reach the AV node, where there is a brief delay allowing the atria to complete pumping blood into the ventricles. Following the pause, the impulses travel through the atrioventricular bundle and bundle branches to the Purkinje fibers, finally causing the ventricles to contract. In contrast, the papillary muscles are involved in the mechanical functioning of the heart by attaching to the heart valves via chordae tendineae and preventing valve inversion, they are not part of the electrical conduction system of the heart.