Hypoglossal nucleus

The hypoglossal nucleusnuclei, existsexist as paired nuclei within the medulla oblongata that provide motor innervation to the intrinsic and extrinsic muscles of the tongue (excluding palatoglossus) via the hypoglossal nerve.

Gross Anatomy

The hypoglossal nuclei are paired nuclei located within the tegmentum of medulla oblongata. It liesThey lie deep to the hypoglossal trigone, or hypoglossal triangle, which is the medial eminence of the floor of the fourth ventricle, inferior to the stria medullaris¹.

TheEach nucleus is approximately 2 cm in length, extending beyond the limits of the hypoglossal trigone into the region of the closed medulla. These nuclei lie ventrally and medially to the dorsal vagal nuclei.

Innervation

The nucleus containsnuclei contain large motor neurons and myelinated fibres of the hypoglossal nerve, innervating the intrinsic and extrinsic tongue muscles, excluding palatoglossus^1,2 (innervated by the vagus nerve).

The hypoglossus receives corticonuclear fibres, from the precentral gyrus and adjoining areas from the both the ipsilateral and contralateral cerebral hemispheres, however primarily from the latter¹. These synaptic connections are made either directly, or indirectly via interneurons.

Functionally, the nucleusnuclei can be divided dorsally and ventrally, and again into medial and lateral components to achieve a musculotopic organisation of the motor neurons within. In this way the dorsal/dorsolateral group innervates the muscles responsible for tongue retraction (hyoglossus, styloglossus), and the ventral/ventromedial group represents the neurons responsible for tongue protrusion (genioglossus)^1,2. The innervation to the intrinsic tongue muscles is less clear.