Nucleus of hypoglossal nerve

At a glance

English

Nucleus of hypoglossal nerve

Latin (TA2)

Nucleus nervi hypoglossi

System

Nerve

Region

Head

Side

Paired, left and right

About the nucleus of hypoglossal nerve

The hypoglossal nucleus is the motor nucleus of the twelfth cranial nerve. It forms a long, slim column in the medulla that runs from the upper part of the open medulla down into the closed medulla below the fourth ventricle, almost the full length of the olive. Like the other somatic motor nuclei it lies close to the midline, and it develops from the basal plate of the embryonic medulla.

In the upper medulla it lies directly under the floor of the fourth ventricle, where it produces a slight elevation, the hypoglossal triangle (trigone), just beside the midline. Lateral to it is the vagal triangle, which covers the vagus nerve's dorsal motor nucleus, so the hypoglossal nucleus sits between that vagal nucleus and the midline. Lower down, where the medulla closes, it lies just in front of the central canal. Its axons run forwards through the medulla, passing lateral to the medial lemniscus, and leave as a row of rootlets in the anterolateral sulcus, between the pyramid and the olive.

The cells are arranged in groups that match the muscles they serve: the intrinsic muscles that change the shape of the tongue and the extrinsic genioglossus, hyoglossus and styloglossus that move it. The nucleus receives corticobulbar fibres from both motor cortices, with the opposite side dominant, especially for genioglossus. It is also tied to the reticular formation and to sensory nuclei such as the solitary and trigeminal nuclei, which coordinate the tongue automatically in swallowing, chewing, sucking and speech.

Damage to the nucleus behaves like damage to the nerve. The tongue on that side wastes, twitches at rest and points towards the weak side when put out. Because the two nuclei lie side by side, a midline lesion can affect both, causing a thick, clumsy tongue with slurred speech and difficulty swallowing. Motor neuron disease often attacks the nucleus early, and a stroke of the medial medulla can damage it along with the pyramid, giving tongue weakness on one side and limb weakness on the other.

Course and supply

Supplies

Holds the lower motor neurons for all intrinsic tongue muscles and for genioglossus, hyoglossus and styloglossus, controlling tongue shape and movement.

Blood supply

Paramedian branches of the vertebral arteries and the anterior spinal artery, which supply the medial medulla.