Which cranial nerve is numbered X in humans?

Cranial nerve X in humans is the vagus nerve.

The vagus is the tenth of the traditional twelve pairs of cranial nerves. It emerges from the medulla oblongata, leaves the skull through the jugular foramen, and travels through the neck into the chest and abdomen. Its name comes from the Latin vagus, meaning “wandering,” describing its extensive route.

Unlike purely sensory nerves such as the optic nerve or mainly motor nerves such as the hypoglossal nerve, the vagus carries both sensory and motor fibers. It provides parasympathetic signals to the heart, lungs, and much of the digestive tract, helping regulate functions such as heart rate, swallowing, voice, and intestinal movement.

A common mix-up is confusing the vagus nerve with cranial nerve IX, the glossopharyngeal nerve. Both participate in the gag reflex, but they have different numbers and major distributions. The vagus is also associated with the “rest-and-digest” response, though it performs broader sensory, motor, and autonomic roles than that nickname suggests.