If left to its own devices, the heart would beat at a rate of around 100 beats per minute. This phenomenon is due to the fact that the SA node in the heart has the ability to self-stimulate - it will depolarize and repolarize without outside influence. Fortunately, the heart is constantly tweaked by both sympathetic and parasympathetic systems in response to environmental cues. Which of the following are the CHIEF nerves responsible for transmitting parasympathetic messages to the heart?
Explanation
Answer: C - Two bundles of parasympathetic nerves - known as Vegas nerves - make contact with both the SA and AV nodes of the heart. At their distal or terminal end, they both release acetylcholine; this dampens the activity of both nodes, thus reducing heart rate. In contrast, the cardiac accelerator nerves release epinephrine and norepinephrine, hormones which relay the wishes of the sympathetic nervous system. Typically, the net response of such stimulation of the cardiac accelerator nerves is a faster heart beat and a more powerful contraction.
