Final answer:
Parasympathetic stimulation to the SA Node increases potassium permeability, leading to a decrease in heart rate, while sympathetic stimulation increases sodium and calcium permeability, increasing heart rate.
Step-by-step explanation:
Parasympathetic stimulation to the SA Node cells will cause a decrease in heart rate by increasing potassium permeability. This occurs as acetylcholine (ACh) released from the vagus nerve upon parasympathetic stimulation opens chemical- or ligand-gated potassium ion channels, which slows the rate of spontaneous depolarization by extending repolarization. This increased permeability to potassium ions increases the time before the next spontaneous depolarization action potentials occur, thereby slowing the heart rate. In contrast to parasympathetic stimulation, sympathetic stimulation increases heart rate by increasing sodium and calcium ion permeability, due to the neurotransmitter norepinephrine (NE).
Parasympathetic stimulation to the SA Node cells will decrease the calcium permeability and thereby decrease heart rate. Parasympathetic stimulation originates from the cardioinhibitory region with impulses traveling via the vagus nerve. It releases the neurotransmitter acetylcholine (ACh), which slows down the heart rate by opening potassium ion channels.