Everything about The Hypoglossal Nerve totally explained
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 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 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's 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). This is another way of saying that the tongue will point to the affected side.
Additional images
Image:Gray559.png|Veins of the tongue. The hypoglossal nerve has been displaced downward in this preparation.
Image:Gray694.png|Section of the medulla oblongata at about the middle of the olive.
Image:Gray699.png|Diagram showing the course of the arcuate fibers.
Image:Gray714.png|Transverse section passing through the sensory decussation.
Image:Gray719.png|Hind- and mid-brains; postero-lateral view.
Image:Gray792.png|Upper part of medulla spinalis and hind- and mid-brains; posterior aspect, exposed in situ.
Image:Gray795.png|Plan of hypoglossal nerve.
Image:Gray1013.png|The mouth cavity.
Further Information
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