Nerve
Hypoglossal nerve (CN XII)
The main cranial motor pathway to the tongue
High-yield
CN XII supplies intrinsic tongue muscles and genioglossus, hyoglossus and styloglossus; palatoglossus is supplied through CN X. Unilateral lower motor neuron injury usually makes the protruded tongue point toward the weak side. Wasting and fasciculations can develop with denervation.
Overview
Motor axons from the hypoglossal nucleus leave the medulla between the pyramid and olive, then pass through the hypoglossal canal. In the neck, the nerve turns forward toward the floor of the mouth and travels lateral to hyoglossus. It controls tongue muscles used for speech and swallowing. Cervical fibers join it temporarily, so the peripheral nerve also carries fibers whose origins are outside the hypoglossal nucleus.
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Reference facts
- Origin
- Hypoglossal motor nucleus near the medullary midline; rootlets emerge from the preolivary sulcus between the pyramid and olive
- Skull exit
- Hypoglossal canal in the occipital bone, superior to the occipital condyle
- Course
- Leaves the skull near the carotid–jugular region, turns forward across the carotid vessels and passes deep to posterior digastric. In the mouth floor it lies lateral to hyoglossus and inferior to the lingual nerve and submandibular duct
- Motor
- Intrinsic tongue muscles plus genioglossus, hyoglossus and styloglossus. Accompanying C1 fibers supply geniohyoid and thyrohyoid and contribute to the superior ansa cervicalis root; these are not hypoglossal-nucleus axons
- Sensory
- No conventional tongue taste or mucosal sensory territory is assigned to CN XII. Sensory and sympathetic fibers can join its extracranial course through cervical connections, so 'purely motor' describes its central origin rather than every peripheral fiber
Mnemonic
On protrusion, the stronger genioglossus pushes the tongue toward the weaker side: tongue tip toward the damaged lower motor pathway.
Clinical correlation
A medial medullary lesion can combine ipsilateral tongue weakness with contralateral limb weakness and impaired vibration or position sense. The complete pattern is not always present. The nerve's cervical course also makes it vulnerable during surgery around the carotid vessels or submandibular region.
Frequently asked questions
Where does the hypoglossal nerve (CN XII) arise?
Hypoglossal motor nucleus near the medullary midline; rootlets emerge from the preolivary sulcus between the pyramid and olive.
What muscles does the hypoglossal nerve (CN XII) supply?
Intrinsic tongue muscles plus genioglossus, hyoglossus and styloglossus. Accompanying C1 fibers supply geniohyoid and thyrohyoid and contribute to the superior ansa cervicalis root; these are not hypoglossal-nucleus axons.
What is the sensory distribution of the hypoglossal nerve (CN XII)?
No conventional tongue taste or mucosal sensory territory is assigned to CN XII. Sensory and sympathetic fibers can join its extracranial course through cervical connections, so 'purely motor' describes its central origin rather than every peripheral fiber.
Where does the hypoglossal nerve (CN XII) leave the skull?
Hypoglossal canal in the occipital bone, superior to the occipital condyle.