Patient had a tongue biopsy. Chief complaint: tongue deviates to the right. Who/what is responsible for the deviation?

Correct answer: A. Right hypoglossal nerve (CN XII)

• A. Correct. The genioglossus muscle (innervated by CN XII) protrudes the tongue contralaterally to the side it's on; when one hypoglossal nerve is damaged, the tongue deviates TOWARD the side of the lesion/damage upon protrusion. With deviation to the right, the right hypoglossal nerve is implicated.
• B. Damage to the left hypoglossal nerve would cause deviation toward the LEFT, not the right.
• C. The vagus nerve (CN X) is not responsible for tongue muscle motor function; it's primarily involved in pharyngeal/laryngeal and visceral functions.
• D. Same reasoning as above — the vagus nerve is not responsible for tongue deviation.

Note: The tongue deviates TOWARD the side of the damaged hypoglossal nerve upon protrusion.