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Hypoglossal Nerve

Q: Which nerve roots form the ansa cervicalis?

The ansa cervicalis is formed by superior and inferior roots derived from upper cervical spinal nerves and the hypoglossal nerve. Superior root (radix superior) — formed by transit motor fibers from the C1 spinal segment traveling within the hypoglossal nerve (n. hypoglossus).Inferior root (radix inferior) — formed by motor branches from segments C2 and C3 (and occasionally C3–C4). By joining together, these roots form the ansa cervicalis, whose branches innervate the infrahyoid muscles of the neck.

Q: Where is the motor nucleus of CN XII located?

The motor nucleus (nucleus n. hypoglossi) is located in the dorsal medulla oblongata and projects onto the floor of the rhomboid fossa within the hypoglossal trigone.

Nervus hypoglossus

For medical students2 min readUpdated 2026-10-10

Hypoglossal nerve is the twelfth cranial nerve (CN XII). It is a purely motor nerve whose primary function is the motor innervation of the intrinsic and extrinsic muscles of the tongue.

Nerve TypePurely motor nerve

Main FunctionMotor innervation of tongue muscles

Nucleus LocationMedulla oblongata (projecting to the rhomboid fossa)

Skull ExitHypoglossal canal (*canalis n. hypoglossi*)

Nucleus and Brainstem Exit

The hypoglossal nerve has a single motor nucleus — the hypoglossal nucleus (nucleus n. hypoglossi). It lies in the dorsal region of the medulla oblongata. On the floor of the rhomboid fossa, this nucleus projects to form the hypoglossal trigone (trigonum n. hypoglossi).

The nerve trunk forms as multiple rootlets emerge from the brainstem rather than a single large bundle. Specifically, 10 to 15 rootlets emerge from the ventrolateral sulcus located strictly between the pyramid and the olive of the medulla oblongata.

Topography and Skull Exit

After exiting the brainstem, the multiple rootlets unite to form the main trunk of the hypoglossal nerve. This trunk leaves the cranial cavity through a dedicated bony opening — the hypoglossal canal (canalis n. hypoglossi).

Immediately after exiting the skull, the nerve begins its complex cervical course, characterized by close syntopy with major blood vessels:

First, the trunk travels downward, lying in the space between the vagus nerve and the internal jugular vein.
It then loops laterally around the internal carotid artery.
Continuing its path, the nerve passes between the internal carotid artery and the internal jugular vein.
Lower down, it crosses the external carotid artery.
Finally, the nerve passes deep to the posterior belly of the digastric muscle before reaching its destination in the tongue muscles.

Branches of the Hypoglossal Nerve

During its course, the nerve gives off several significant groups of branches:

Lingual branches (rr. linguales) — these are the terminal branches of the twelfth cranial nerve. They penetrate the tongue and supply both its intrinsic and extrinsic muscles.
Meningeal branches — small branches that arise from the main trunk at the beginning of its course while the nerve is still within the hypoglossal canal.
Communicating branches — form a network of connections with other neural structures. The hypoglossal nerve communicates with:
the superior cervical sympathetic ganglion;
the inferior ganglion of the vagus nerve;
the lingual nerve (a branch of the trigeminal nerve — n. trigeminus);
the ansa cervicalis, which carries motor fibers from spinal segments C1–C3.

Mnemonic

To remember the exit site from the brain, use the rule: The hypoglossal nerve emerges from the sulcus Between the Pyramid and the Olive (BPO).

Frequently asked questions

What are the symptoms of a unilateral hypoglossal nerve lesion?

Symptoms of a unilateral hypoglossal nerve lesion include motor deficits of the ipsilateral half of the tongue and speech disorders. In peripheral or nuclear lesions, the following signs are observed:

Tongue deviation — deviates toward the side of the lesion upon protrusion.
Muscle atrophy — of the ipsilateral half of the tongue.
Fasciculations — involuntary muscle twitches.
Dysarthria — impaired speech articulation.
Weakness in pushing — toward the paralyzed side (paresis of the genioglossus muscle).

Swallowing remains largely intact. Unilateral supranuclear lesions do not cause profound tongue mobility deficits due to bilateral cortical innervation.

Which nerve roots form the ansa cervicalis?

The ansa cervicalis is formed by superior and inferior roots derived from upper cervical spinal nerves and the hypoglossal nerve.

Superior root (radix superior) — formed by transit motor fibers from the C1 spinal segment traveling within the hypoglossal nerve (n. hypoglossus).
Inferior root (radix inferior) — formed by motor branches from segments C2 and C3 (and occasionally C3–C4).

By joining together, these roots form the ansa cervicalis, whose branches innervate the infrahyoid muscles of the neck.

What is the functional type of the hypoglossal nerve?

The hypoglossal nerve is exclusively a motor nerve. It contains no dedicated sensory or parasympathetic nuclei.

Where is the motor nucleus of CN XII located?

The motor nucleus (nucleus n. hypoglossi) is located in the dorsal medulla oblongata and projects onto the floor of the rhomboid fossa within the hypoglossal trigone.

How does the trunk of the hypoglossal nerve leave the cranial cavity?

After merging from 10–15 rootlets, the main nerve trunk exits the cranial cavity through the hypoglossal canal (canalis n. hypoglossi).

Go deeper

Projection of the hypoglossal nucleus onto the rhomboid fossa (trigonum n. hypoglossi).
Detailed topography of the nerve relative to the internal and external carotid arteries.
Formation of anastomoses and communicating branches (ansa cervicalis, C1–C3 fibers).
Innervation patterns of intrinsic and extrinsic tongue muscles by terminal branches (rr. linguales).