Hypoglossal Nerve (Cranial Nerve XII)

Dr. Mohamed Alzain Mohamed

إن الرجل ليلقي بالكلمة )� فتهوي به ًال يلقي لها باًال� في جهنم (سبعين خريفا

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hypoglossal nerve is a motor nerve that supplies all the intrinsic muscles of the tongue as well as the styloglossus, the hyoglossus, and the genioglossus muscles.

Muscles of Tongue

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Components

GSA

Hypoglossal Nucleus

beneath the floor of the lower part of the fourth ventricle .

receives corticonuclear fibers from both cerebral hemispheres.

cells responsible for supplying the genioglossus muscle only receive corticonuclear fibers from the opposite cerebral hemisphere.

Course of the Hypoglossal Nerve

emerge on the anterior surface of the medulla oblongata between the pyramid and the olive .

leaves the skull through the hypoglossal canal.

between the internal carotid artery and the internal jugular vein .

passes deep to the posterior margin of the mylohyoid muscle lying on the lateral surface of the hyoglossus muscle.

Hypoglossal nerve lesions

Damage to the hypoglossal nerve in the neck would result in an ipsilateral lower motor neuron lesion.

This would cause the protruded tongue to deviate to the side of the lesion. Why ?

Lingual nerve is at risk during removal of the lower third molar or during operations of the submandibular gland / duct

Damage to the hypoglossal nerve – tongue deviates to the paralyzed side; longstanding paralysis wasting of the muscles

Normal

Paralysis

Normal genioglossus pulls the same side forwards leaving the paralyzed side stationary

why?

If a patient has a lesion of the corticonuclear fibers upper motor neuron.

on protrusion, the tongue will deviate to the side opposite the lesion. Why ?

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