Anatomy Atlas

Hypoglossal nerve (CN XII)

Nervus hypoglossus
Also: CN XII · Cranial nerve XII
NerveHigh-yielddraftNeuro

Motor nerve to the tongue. A lower motor neuron lesion makes the protruded tongue deviate toward the weak side, with atrophy and fasciculations.

Core anatomy

Origin

Hypoglossal nucleus in the floor of the fourth ventricle in the medulla oblongata; rootlets emerge in the preolivary sulcus between the pyramid and the olive.

Course

Leaves the skull through the hypoglossal canal → descends between the internal carotid artery and internal jugular vein → loops forward around the occipital artery → crosses superficial to the internal and external carotid arteries above the bifurcation (see common and internal carotid arteries) → runs forward on hyoglossus above the hyoid, below the submandibular duct, into the tongue. C1 fibers travel with it (superior root of the ansa cervicalis, and to thyrohyoid and geniohyoid; see cervical plexus).

Motor

All intrinsic and extrinsic muscles of the tongue except palatoglossus (CN X) — genioglossus, hyoglossus, styloglossus.

Relations

At risk in carotid endarterectomy, submandibular gland excision and neck dissection.

Other structures innervated

Mentioned in

Generated automatically from links in other entries.

Where the cranial nerves leave the brainstem (ventral view)The front of the brainstem. The optic nerves meet at the chiasm above. The oculomotor nerve emerges from the interpeduncular fossa between the cerebral peduncles of the midbrain. The trochlear nerve is the only one to leave from the back, just below the inferior colliculus, and winds forward around the peduncle. The trigeminal nerve leaves the lateral pons. The abducens leaves at the pontomedullary junction near the midline; the facial and vestibulocochlear nerves leave at the cerebellopontine angle. The glossopharyngeal and vagus nerves leave the postolivary sulcus of the medulla, the hypoglossal leaves the preolivary sulcus between the pyramid and the olive, and the accessory nerve rises from the upper cervical cord.Optic (II)Oculomotor (III)Trochlear (IV) — from the dorsal sideTrigeminal (V)Abducens (VI)Facial (VII)Vestibulocochlear (VIII)Glossopharyngeal (IX)Vagus (X)Accessory (XI) — from C1–C5Hypoglossal (XII)Midbrain (cerebral peduncle)PonsPyramidOliveSpinal cordMedullaVentral view · dashed IV leaves from the back

Swipe sideways to see the whole diagram →

Where the cranial nerves leave the brainstem. Ventral view. III leaves the interpeduncular fossa of the midbrain; IV is the only nerve to leave from the back (dashed); V leaves the lateral pons; VI the pontomedullary junction near the midline; VII and VIII the cerebellopontine angle; IX and X the postolivary sulcus; XII the preolivary sulcus between pyramid and olive; and XI rises from the upper cervical cord. Nuclei follow the same levels: III–IV midbrain, V–VIII pons, IX–XII medulla.
Original schematic, created for this atlas.
Lateral dissection of the neck showing the hypoglossal nerve, the ansa cervicalis on the carotid sheath, the cervical plexus, the common carotid artery and internal jugular vein
The hypoglossal nerve crossing the carotid arteries on its way to the tongue.
Henry Vandyke Carter, Gray's Anatomy of the Human Body, 20th ed. (1918), Fig. 794. Source · Public domain (Public domain in the US: published before January 1, 1931 (per Wikimedia Commons))

Clinical correlations

Hypoglossal nerve lesion PANCE

Mechanism / lesion

LMN: skull-base tumors, carotid dissection, carotid endarterectomy, medial medullary stroke, ALS (bulbar, with fasciculations). UMN: contralateral cortical/corticobulbar stroke.

Classic presentation

LMN: tongue deviates toward the side of the lesion on protrusion (the intact genioglossus pushes it over), with ipsilateral atrophy and fasciculations, dysarthria. UMN: the tongue deviates away from the cortical lesion (toward the weak side of the body) without atrophy; often mild because of partly bilateral input.

Medial medullary syndrome PANCE

Mechanism / lesion

Occlusion of the anterior spinal artery or vertebral branches supplying the medial medulla.

Classic presentation

Ipsilateral tongue deviation/atrophy (XII), contralateral hemiparesis (pyramid) and contralateral loss of vibration and proprioception (medial lemniscus).

High-yield PANCE pearls

  • Tongue deviates toward a CN XII LMN lesion ("lick your wounds").
  • Tongue atrophy + fasciculations → LMN (e.g. ALS).
  • Ipsilateral tongue weakness + contralateral hemiparesis + contralateral loss of proprioception → medial medullary syndrome.
  • Tongue deviation after carotid endarterectomy → CN XII injury.

Imaging anatomy

MRI

MRI brain and skull base (hypoglossal canal), with MRA or CTA of the neck when carotid dissection is possible.

Physical exam

Strength / function testing

Inspect the tongue at rest in the mouth (atrophy, fasciculations — look at rest, since protrusion causes normal tremor), then on protrusion (deviation), side-to-side movement and pushing against the cheek; speech ("la-la-la").

Self-quiz

Q1.

A patient has sudden right-sided weakness and loss of vibration sense in the right limbs. Her tongue deviates to the left on protrusion. Where is the lesion?

Show answer

B

Left medial medullary syndrome: left CN XII (tongue deviates to the left), left pyramid (right hemiparesis — the pyramids decussate below) and left medial lemniscus (right-sided loss of vibration/proprioception — already crossed).

Q2.

Which tongue muscle is NOT supplied by the hypoglossal nerve?

Show answer

D

Palatoglossus is supplied by the vagus (pharyngeal plexus); all other tongue muscles are supplied by CN XII.

Q3.

In an upper motor neuron (cortical) lesion of hypoglossal control, how does the tongue behave?

Show answer

B

An LMN lesion makes the tongue deviate toward the lesion with atrophy and fasciculations. A UMN (cortical) lesion makes it deviate away from the cortical lesion (toward the weak side of the body), without atrophy, and is often mild.

Q4.

Through which opening does the hypoglossal nerve leave the skull?

Show answer

D

CN XII exits through the hypoglossal canal, just anterolateral to the foramen magnum. CN IX–XI use the jugular foramen.

Q5.

In the neck, the hypoglossal nerve crosses which vessels, making it vulnerable in carotid surgery?

Show answer

E

The hypoglossal nerve loops forward superficial to the internal and external carotid arteries above the bifurcation, so it is at risk during carotid endarterectomy.

Flashcards

See also