This nerve innervates the tongue and, when injured, causes the tongue to deviate toward the side of the lesion. Which nerve is it?

This nerve innervates the tongue and, when injured, causes the tongue to deviate toward the side of the lesion. Which nerve is it?

• A. Glossopharyngeal IX
• B. Vagus X
• C. Hypoglossal XII
• D. Accessory XI

Answer: (C)

Tongue deviation on protrusion points to a problem with the nerve that supplies the tongue muscles. The hypoglossal nerve carries motor input to all intrinsic tongue muscles and most of the extrinsic tongue muscles (notably the genioglossus, which mainly protrudes the tongue). When one side is damaged, the genioglossus on that side becomes weak, and the intact muscles on the opposite side pull the tongue toward the damaged side. This is the classic sign of a lower motor neuron lesion of the hypoglossal nerve. The other nerves listed don’t move the tongue in this coordinated way: glossopharyngeal is involved more with swallowing and posterior tongue sensation; vagus supplies the palatoglossus among other functions; accessory moves neck muscles. If the deviation were away from the lesion, that would suggest an upper motor neuron pattern rather than a direct hypoglossal nerve injury.

Tongue deviation on protrusion points to a problem with the nerve that supplies the tongue muscles. The hypoglossal nerve carries motor input to all intrinsic tongue muscles and most of the extrinsic tongue muscles (notably the genioglossus, which mainly protrudes the tongue). When one side is damaged, the genioglossus on that side becomes weak, and the intact muscles on the opposite side pull the tongue toward the damaged side. This is the classic sign of a lower motor neuron lesion of the hypoglossal nerve. The other nerves listed don’t move the tongue in this coordinated way: glossopharyngeal is involved more with swallowing and posterior tongue sensation; vagus supplies the palatoglossus among other functions; accessory moves neck muscles. If the deviation were away from the lesion, that would suggest an upper motor neuron pattern rather than a direct hypoglossal nerve injury.