Final answer:
The hypoglossal nerve, or twelfth cranial nerve, primarily controls the tongue muscles and is vital for functions such as speaking and swallowing. It is tested through the 'stick out your tongue' exam, where the straight or deviated protrusion indicates nerve health or damage respectively.
Step-by-step explanation:
The hypoglossal nerve, also known as the twelfth cranial nerve, is vital for the control of the muscles of the tongue. This nerve enables important functions such as speech and swallowing. It is responsible for the majority of tongue movements, excluding the palatoglossus muscle, which is innervated by the vagus nerve. To assess the function of the hypoglossal nerve, doctors perform a simple test where they ask the patient to 'stick out your tongue'. If the nerve is functioning correctly, the tongue should protrude straight out. However, if there is a deficit on one side, the tongue will deviate towards the side of the damage, suggesting potential nerve impairment or lesions in the brainstem adjacent to other critical centers for bodily functions.
Motion and strength of the tongue are controlled by the genioglossus muscle, with nerves originating from a nucleus near the cardiovascular and respiratory regulatory centers in the brainstem. Damage to this nerve or its nucleus can not only affect tongue function but can also indicate issues with nearby structures that manage different physiological processes.