Final answer:
The pacemaking activity of the SA node is regulated by both intrinsic factors within the heart, such as the SA and AV nodes, and extrinsic factors from the autonomic nervous system. Parasympathetic stimulation slows down the heart rate, while sympathetic stimulation speeds it up.
Step-by-step explanation:
The pacemaking activity of the SA node is regulated by several factors. One of the main regulators is the sinoatrial (SA) node itself, which is located near the wall of the right atrium. The SA node acts as the heart's internal pacemaker, initiating the electrical signals that time the beating of the heart. Other regulators include the atrioventricular (AV) node, the bundle of His, the bundle branches, and the Purkinje fibers, which together ensure the coordinated contraction of the atria and ventricles.
Additionally, the pacemaking activity of the SA node is also regulated by the autonomic nervous system. Parasympathetic stimulation, mediated by the vagus nerve, slows down the heart rate by releasing the neurotransmitter acetylcholine (ACh) at the neuromuscular junction. On the other hand, sympathetic stimulation, mediated by the release of norepinephrine and epinephrine, speeds up the heart rate.
Overall, the pacemaking activity of the SA node is regulated by both intrinsic factors within the heart and extrinsic factors from the autonomic nervous system.