Which cranial nerve provides parasympathetic supply to the heart?

• A. Glossopharyngeal nerve
• B. Facial nerve
• C. Accessory nerve
• D. Vagus nerve

Answer: (D)

Parasympathetic control of the heart is carried by the vagus nerve. Its preganglionic fibers originate in the medulla and reach the cardiac plexus, where they synapse on intrinsic cardiac ganglia. The postganglionic neurons release acetylcholine, which acts on M2 muscarinic receptors in the SA and AV nodes to slow heart rate and decrease conduction. The other cranial nerves don’t provide parasympathetic innervation to the heart: glossopharyngeal mainly targets the parotid gland, facial nerve targets lacrimal and salivary glands, and the accessory nerve is motor to neck muscles. Therefore, the vagus nerve is responsible for parasympathetic supply to the heart.