What is the main function of the hypoglossal nerve (CN XII)?

The hypoglossal nerve is a purely motor nerve that supplies all intrinsic and extrinsic muscles of the tongue, controlling movements like protrusion and retraction.

Where does the hypoglossal nerve originate in the brain?

It originates from the hypoglossal nucleus in the medulla oblongata, with rootlets emerging between the pyramid and olive on the ventral medulla.

What happens if the hypoglossal nerve is damaged on one side?

Unilateral damage causes lower motor neuron paralysis of the ipsilateral tongue muscles. On protrusion, the tongue deviates toward the paralyzed side due to unopposed action of the healthy muscles.

How is the hypoglossal nerve tested clinically?

Clinical testing involves assessing genioglossus function by asking the patient to protrude the tongue. Deviation or inability to protrude indicates hypoglossal nerve dysfunction.

What muscles does the hypoglossal nerve supply, and are there any exceptions?

It supplies all tongue muscles except the palatoglossus, which is innervated by the cranial accessory nerve via the pharyngeal plexus.

What is the course of the hypoglossal nerve after it exits the skull?

After exiting through the hypoglossal canal, it descends between the internal carotid artery and internal jugular vein, curves forward crossing carotid and lingual arteries, and runs superficial to the hypoglossus muscle to reach the tongue.

What are the branches of the hypoglossal nerve, and what do they do?

Branches include hypoglossal proper branches that supply tongue muscles, and branches with C1 fibers like meningeal, descendens hypoglossi, and nerves to thyrohyoid and geniohyoid muscles.

Hypoglossal Nerve (CN XII) – Tongue Motor Control

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