QS Study

The Hypoglossal nerve is a motor nerve. It is the 12th cranial nerve and controls movements of the tongue. The nerve has a with the sole purpose somatic motor function, innervating the majority of the muscles of the tongue.

Nucleus

The hypoglossal nucleus is situated in the lower part of the floor of the fourth ventricle.

Course

The nerve fiber emerges on the inferior surface of the medulla oblongata between the pyramid and olive. It crosses the posterior cranial fossa and leaves the skull through the hypoglossal canal. Then it passes downward and forward in the neck between the internal carotid artery and the internal jugular vein until it reaches the lower border of the posterior belly of digastric muscle. Then it passes deep to the mylohyoid muscle. In the upper part of its course, the hypoglossal nerve joined by C1 fibers from the cervical plexus. These fibers do not combine with the hypoglossal nerve – they merely travel within its sheath.

Hypoglossal Nerve 1

Fig: Course of Hypoglossal Nerve

Intracranial Course: CN XII emerges from the brainstem as a series of rootlets which converge to form the hypoglossal nerve. The nerve exits the cranium via the hypoglossal foramen in the posterior cranial fossa.

Extracranial Course and Final Innervation: Upon exiting the skull, the hypoglossal nerve lies medial to CNs IX, X, and XI which exited the skull via the jugular foramen.

Distribution

It supplies all the intrinsic muscles of the tongue and also the styloglossus, hyoglossus, the genioglossus muscle. Thus it controls the movement and shape of the tongue. They supply all the muscles of the tongue with the exception of palatoglossus that is supplied by the cranial root of accessory through the pharyngeal plexus.

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