The hypoglossal nerve (in English “hypoglossal nerve”) constitutes the twelfth nerve of the group of twelve cranial nerves (XII cranial nerve) and is the motor nerve of thetongue.
The hypoglossal nerve innervates the intrinsic and extrinsic muscles of the tongue allowing its movements and its functioning is essential for speaking, chewing and swallowing in a normal way.
As a pure somatomotor, the hypoglossal nerve has only one nucleus per antimer; originates in a nucleus located in the dorsal part of the bulb, emerges in the antero-lateral sulcus that separates the olive from the pyramid as a longitudinal series of radicles that meet in two-three trunks and then in a single nerve that emerges from the skull passing through the hypoglossal canal. After its emergence from the canal of the same name, it moves laterally to the vagus nerve, and passes through the interstice between the internal carotid artery and the internal jugular vein. At this point it goes almost vertically between the two vessels, in front of the vagus nerve, and reaches the corner of the jaw. After passing under the posterior belly of the digastric muscle, it enters the submandibular region and then the tongue.
Nerve damage at the level of the lower motor neuron can lead to atrophy of the muscles of the tongue or fasciculations of the tongue (“bag of worms”). Damage to the upper motor neuron will not lead to atrophy or fasciculations, but only weakness of the innervated muscles. When the nerve is damaged, weakness of the movement of the tongue on one side will occur. If the damage is particularly extensive, the tongue will move to the weaker side. Hypoglossal nerve damage can ultimately result in difficulty speaking, chewing, and swallowing.
Possible causes of injury, inflammation, compression or damage to the hypoglossal nerve are:
- amyotrophic lateral sclerosis;
- bone abnormality at the base of the skull;
- brain stroke;
- brain stem infection;
- neck injury, such as in the surgical removal of a neck artery obstruction (endarterectomy).