Final answer:
The intrinsic rate of the AV node is D) 40-60 bpm. The AV node can control the heart rate at this range when acting independently of the SA node. Both parasympathetic and sympathetic systems can modify this intrinsic heart rate.
Step-by-step explanation:
The intrinsic rate of the AV (atrioventricular) node is D) 40-60 bpm (beats per minute). The AV node is capable of generating its own impulses independently. Without the influence of the SA (sinoatrial) node, the AV node would generally control the heart rate at 40-60 bpm. This rate of impulse generation in the AV node is slower than that of the SA node, which would normally generate impulses at approximately 80-100 bpm without external influences such as nervous or endocrine control.
Parasympathetic and sympathetic nervous systems play a role in modifying this intrinsic rate. Parasympathetic stimulation, mainly through the release of acetylcholine (ACh), slows down heart rate, while sympathetic stimulation tends to increase it. It's important to note that the SA node generally sets the pace for the heart rate because it has the highest automaticity or propensity to depolarize, and other parts of the conduction system, including the AV node, typically follow its lead unless there is some form of blockage or dysfunction.