hypoglossal nerve

Nerve: Hypoglossal nerve
Hypoglossal nerve, cervical plexus, and their branches.
Inferior view of the human brain, with the cranial nerves labelled.
Latin	nervus hypoglossus
Gray's	subject #207 914
Innervates	genioglossus, hyoglossus, styloglossus
To	ansa cervicalis
MeSH	Hypoglossal+Nerve

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 vagus nerve (cranial nerve X) or, according to some classifications, by fibers from the glossopharyngeal nerve (cranial nerve IX) that "hitchhike" within the vagus.

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.

Paralysis/paresis of one side of the tongue results in ipsilateral curvature of the tongue (apex toward the impaired side of the mouth) i.e., the tongue will move towards the affected side.

External links

• NeuroNames hier-701
• MedEd at Loyola GrossAnatomy/h_n/cn/cn1/cn12.htm
• cranialnerves at The Anatomy Lesson by Wesley Norman (Georgetown University) (XII)