Which cranial nerve provides most of the parasympathetic outflow to the thorax and abdomen?

• A. CN IX, Glossopharyngeal
• B. CN III, Oculomotor
• C. CN X, Vagus
• D. CN VII, Facial

Answer: (C)

Parasympathetic innervation to the thorax and abdomen is provided predominantly by the vagus nerve. Its preganglionic fibers originate in the dorsal motor nucleus of the vagus and travel to the heart, lungs, and most of the gastrointestinal tract through a network of thoracic and abdominal plexuses, then synapse in intrinsic (intramural) ganglia within the target organs. This brings about the usual “rest and digest” effects: slowing heart rate, constricting airways, increasing GI motility and secretions, and coordinating organ function along the upper to mid-gut.

The other cranial nerves carry parasympathetic fibers, but mainly to structures in the head and neck: the oculomotor nerve to the eye, the facial nerve to lacrimal and salivary glands, and the glossopharyngeal nerve to the parotid gland. They do not provide the major parasympathetic supply to thoracic and abdominal viscera, which is why the vagus is the correct choice.