Final answer:
The target of sympathetic and parasympathetic innervation in the heart's conducting system is both the sinoatrial (SA) node and the atrioventricular (AV) node. The AV node has the slowest rate of firing of the components listed. The correct option is b.
Step-by-step explanation:
The structures in the conducting system of the heart that are the 'targets' of sympathetic and parasympathetic innervation are the sinoatrial (SA) node and the atrioventricular (AV) node. The SA node, often referred to as the pacemaker of the heart, initiates the heartbeat and sets the pace for cardiac function. The AV node receives the electrical signal from the SA node and provides a crucial delay to ensure that the atria have time to empty their blood into the ventricles before the ventricles contract.
As for which component of the heart conduction system would have the slowest rate of firing, the correct answer is the atrioventricular node (a). The specialized conducting components of the heart, listed generally in the order of the electrical conduction pathway, include the SA node, the internodal pathways, the AV node, the atrioventricular bundle (or bundle of His), the right and left bundle branches, and the Purkinje fibers. The rate of firing of these components decreases as the impulse travels from the SA node to the AV node, making the AV node the one with the slowest intrinsic rate of firing among these options.