In a healthy resting individual, heart rate is slowed by: A. the AV node pacemaker B. catecholaminergic stimulation of the sympathetic fibers of the dorsal root ganglion C. node of ranvier nodal block D. All of the above E. None of the above

• None of the above

Explanation:

During resting, the sympathetic nervous system releases hormones such as norepinephrine, epinephrine and catecholamines, which accelerates the heart rate. SA node controls heart rate but does not slow it, it ensures the heart rate is normal by firing regularly. AV node controls the ventricles and not the heart rate. So none of the above.