The hypoglossal nerve arises as a number of small rootlets from the front of the medulla, the bottom part of the brainstem,[1][2] in the anterolateral sulcus which separates the olive and the pyramid.

[3] The nerve passes through the subarachnoid space and pierces the dura mater near the hypoglossal canal, an opening in the occipital bone of the skull.

[4] At a point at the level of the angle of the mandible, the hypoglossal nerve emerges from behind the posterior belly of the digastric muscle.

[4] It then loops around a branch of the occipital artery and travels forward into the region beneath the mandible.

[2] Neurons of the hypoglossal nucleus are derived from the basal plate of the embryonic medulla oblongata.

[7][8] The musculature they supply develops as the hypoglossal cord from the myotomes of the first four pairs of occipital somites.

[13] The hypoglossal nerve also supplies movements including clearing the mouth of saliva and other involuntary activities.

The hypoglossal nucleus interacts with the reticular formation, involved in the control of several reflexive or automatic motions, and several corticonuclear originating fibers supply innervation aiding in unconscious movements relating to speech and articulation.

[14] The most common causes of injury in one case series were compression by tumours and gunshot wounds.

These include surgical damage, medullary stroke, multiple sclerosis, Guillain-Barre syndrome, infection, sarcoidosis, and presence of an ectatic vessel in the hypoglossal canal.

Such a stroke may result in tight oral musculature, and difficulty speaking, eating and chewing.

[6] Damage to the hypoglossal nucleus will lead to wasting of muscles of the tongue and deviation towards the affected side when it is stuck out.

[23][24] Certain patients with obstructive sleep apnea who are deemed eligible candidates (e.g., failed continuous positive airway pressure therapy, underwent appropriate testing with drug induced sleep endoscopy, and meet other criteria as outlined by the FDA)[25] may be offered the hypoglossal nerve stimulator as an alternative.

In this procedure, an electrical stimulator lead is placed around branches of the hypoglossal nerve that control tongue protrusion (e.g., genioglossus) via an incision in the neck.

[28] As with humans, damage to the nerve or nerve pathway will result in difficulties moving the tongue or lapping water, decreased tongue strength, and generally cause deviation away from the affected side initially, and then to the affected side as contractures develop.