Stimulation of which nerve will lead to bradycardia and hypotension?

• A. The sympathetic nerve
• B. The vagus nerve
• C. The phrenic nerve
• D. The hypoglossal nerve

Answer: (B)

Parasympathetic control of the heart is being tested here. The vagus nerve provides the main parasympathetic input to the heart. When it’s stimulated, acetylcholine is released onto the SA and AV nodes, binding to M2 muscarinic receptors. This slows the pace of the SA node, lengthens AV conduction, and modestly decreases contractility. The result is a slower heart rate and lower cardiac output, which can lead to hypotension.

In contrast, stimulating the sympathetic nerve would raise heart rate and blood pressure, while the phrenic nerve and hypoglossal nerve mainly control breathing-related diaphragm movement and tongue muscles, with no direct primary effect on heart rate or blood pressure.