Sunday, February 6, 2011

Hypoglossal Nerve (CN XII)

Also known as CN XII, the hypoglossal nerve is the twelfth of twelve paired cranial nerves. The CN XII innervates the muscles of the tongue. It is a somatomotor nerve whose fibers originate in the hypoglossal nucleus neurons situated in the dorsal medulla oblongata of the brainstem. The hypoglossal nucleus nerve cells send axons that exit as rootlets that emerge in the ventrolateral sulcus of the medulla between the olive and pyramid. Then, the rootlets come together to make up the hypoglossal nerve, exiting the cranium through the hypoglossal canal.

As the CN XII comes out of the hypoglossal canal, it gives off a small meningeal branch, picking up a branch from the anterior ramus of C1. Then, 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, the hypoglossal nerve passes to the submandibular region to enter the tongue.