The hypoglossal nerve arises in the medulla oblongata and leaves the skull through the hypoglossal canal in the occipital bone It then comes into close relationship with the ninth, tenth, and eleventh cranial nerves, the internal carotid artery, and in the internal jugular vein. It descends between the internal carotid artery and the internal jugular vein until it reaches the lower border of the posterior belly of the digastric muscle, where it turns forward and medially. The nerve loops around the occipital artery and crosses the internal and external carotid arteries and the loop of the lingual artery. Here, it is crossed by the facial vein. It passes forward and upward, deep to the intermediate tendon of the digastric muscle, the stylohyoid, and the posterior margin of the mylohyoid muscle, between the mylohyoid and the hypoglossus. It lies below the deep part of the submandibular gland, the submandibular duct, and the lingual nerve. At the anterior margin of the hypoglossus, it curves upward toward the tip of the tongue, supplying branches to the muscles.
In the upper part of its course, the hypoglossal nerve is joined by a small branch from the cervical plexus (C1 and sometimes C2). This branch later leaves the hypoglossal nerve as its descending branch, the nerve to the thyrohyoid and the nerve to the geniohyoid.
Branches of the hypoglossal nerveThe meningeal branch of the hypoglossal nerve arises from the nerve as it traverses the hypoglossal canal. It supplies the meninges in the posterior cranial fossa.
The descending branch, which is composed of C1 fibers, arises from the hypoglossal nerve as it curves forward below the posterior belly of the digastric. It descends in front of the internal and common carotid arteries, embedded in the carotid sheath. It is joined by the descending cervical nerve (C2 and C3) from the cervical plexus, to form a loop, called the ansa cervicalis. Branches from the loop supply the omohyoid, the sternohyoid, and the sternothyroid muscles.
Damage to to the hypoglossal nerveThe hypoglossal nerve is rarely damaged. If damage does occur (for example, as a result of a stroke), one side of the tongue becomes paralyzed.
Related category• ANATOMY AND PHYSIOLOGY
Source: Richard S. Snell. Clinical Anatomy for Medical Students, Third Edition. Little, Brown: Boston (1986).
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