Final answer:
The hypoglossal nerve controls tongue movements and is tested by asking a patient to stick out their tongue; if functioning properly, the tongue will protrude straight out.
Step-by-step explanation:
The nerve that controls the movements of the tongue is the hypoglossal nerve, also known as the twelfth cranial nerve. It is responsible for the contraction of the muscles of the tongue, which is critical for functions like speech and swallowing. The genioglossus muscle, which is innervated by the hypoglossal nerve, enables the protrusion of the tongue. If there is a deficit in one side of the hypoglossal nerves, the tongue will deviate towards the affected side when the patient attempts to stick it out, indicating possible nerve damage.
To confirm the hypoglossal nerve's function, a simple test is performed during a clinical exam where the patient is asked to 'stick out your tongue'. Normal function is exhibited when the tongue protrudes straight out. The motor functions of the vagus nerve can also be tested by observing movements of the tongue, soft palate, or superior pharynx during swallowing or during the gag reflex elicitation.