The hypoglossal nerve
is the twelfth cranial nerve
(XII), leading to the tongue. The nerve arises from the hypoglossal nucleus
and emerges from the medulla oblongata
in the preolivary sulcus
separating the olive
and the pyramid
. It then passes through the hypoglossal canal
. On emerging from the hypoglossal canal, it gives off a small meningeal branch and picks up a branch from the anterior ramus
. It spirals behind the vagus nerve
and passes between the internal carotid artery
and internal jugular vein
lying on the carotid sheath
. After passing deep to the posterior
belly of the digastric muscle
, it passes to the submandibular region to enter the tongue
It supplies motor fibres to all of the muscles of the tongue, except the palatoglossus muscle which is innervated by the accessory nerve, which runs in part with the vagus nerve (Cranial nerve X).
Testing the hypoglossal nerve
To test the function of the nerve, a person is asked to poke out their tongue. If there is a loss of function on one side (unilateral paralysis) the tongue will point towards the affected side.
The strength of the tongue can be tested by getting the person to poke the inside of their cheek, and feeling how strongly they can push a finger pushed against their cheek - a more elegant way of testing than directly touching the tongue.
The tongue can also be looked at for signs of lower motor neuron disease, such as fasciculation and atrophy.
Ipsilateral paralysis/paresis of the tongue results in contralateral curvature of the tongue (apex toward the unimpaired side of the mouth) i.e., the tongue will point away from the affected side.