Which cranial nerve provides primary parasympathetic innervation to the heart, lungs, and gastrointestinal tract?
Answer and explanation
Correct answer: A. Vagus nerve
The vagus nerve (CN X) carries ~75% of all parasympathetic efferents, innervating thoracic viscera (heart, lungs) and abdominal organs up to the splenic flexure of the colon. Pelvic splanchnic nerves (S2-S4) supply the hindgut and pelvic organs.
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