Final answer:
The hypoglossal nerve controls the muscles of the tongue, with the exception of the palatoglossus muscle which is controlled by the vagus nerve. Examining the movement of the tongue can assess the function of the hypoglossal nerve, with any side deviation indicating possible nerve damage.
Step-by-step explanation:
The hypoglossal nerve, which is also known as the twelfth cranial nerve, is responsible for the motor control of the muscles of the tongue. All intrinsic and extrinsic muscles of the tongue are supplied by the hypoglossal nerve, except for the palatoglossus muscle that is innervated by the vagus nerve.
The hypoglossal nerve is tested by asking a patient to stick out their tongue, and observing for any deviations to one side, which can indicate nerve impairment.
The genioglossus muscle, one of the extrinsic muscles, plays a crucial role in the protrusion of the tongue. When both sides of the hypoglossal nerves are functioning correctly, the tongue will protrude straight out. If there's an issue with one side, the tongue will deviate towards the damaged side, pointing out potential nerve or adjacent structure issues.
The facial and glossopharyngeal nerves are involved in taste sensation rather than motor control. They play no part in the muscular control of the tongue, but they do carry taste sensations to the brain and contribute to the gag reflex, which involves the vagus nerve.