Final answer:
The vagus nerve, or cranial nerve X, is the parasympathetic nerve that supplies the SA and AV nodes, and it releases acetylcholine to reduce heart rate.Option 1 is the correct answer.
Step-by-step explanation:
The parasympathetic nerve supply to the SA (sinoatrial) and AV (atrioventricular) nodes is provided by the vagus nerve (cranial nerve X). The vagus nerve sends branches to both the SA and AV nodes, as well as to portions of the atria and ventricles, releasing the neurotransmitter acetylcholine (ACh). This neurotransmitter acts by opening chemical- or ligand-gated potassium ion channels, which slows the rate of spontaneous depolarization, lengthens repolarization, and increases the time before the next spontaneous depolarization occurs, thus reducing the heart rate (HR).
The parasympathetic nervous system exerts control over cardiac function by innervating the sinoatrial (SA) and atrioventricular (AV) nodes, primarily through the vagus nerve (cranial nerve X). The vagus nerve extends branches to both nodes, along with sections of the atria and ventricles. Acetylcholine (ACh) serves as the neurotransmitter released by the vagus nerve.
ACh operates by activating ligand-gated potassium ion channels, inducing a cascade of effects that include slowing the rate of spontaneous depolarization, prolonging repolarization, and extending the interval before the next spontaneous depolarization. This orchestrated response orchestrated by ACh results in a reduction in heart rate (HR).