The is the twelfth
Cranial Nerve . The nerve arises from the
Hypoglossal Nucleus and emerges from the
Medulla Oblongata between the ''olive'' and the ''pyramids''. It then passes through the
Hypoglossal Canal . On emerging from the hypoglossal canal, the nerve picks up a branch from the anterior ramus of
C1 . 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 tongue.
It supplies motor fibres to all of the muscles of the
Tongue , except the
Palatoglossus Muscle which is innervated by the
Vagus Nerve (X) and the
Accessory Nerve (XI).
Aside from the tongue, the hypoglossal nerve also controls, via the
Ansa Cervicalis ,
Thyrohyoid Muscle ,
Omohyoid Muscle ,
Sternothyroid Muscle and
Sternohyoid Muscle . The nerve fibres supplying these muscles all come from the C1 contribution.
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 at 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 motorneuron disease, such as
Fasciculation and
Atrophy .
