Hypoglossi

Hypoglossi is the plural form of the term referring to the hypoglossal nerves, cranial nerve XII. These are paired motor nerves that supply most of the tongue’s intrinsic muscles and several extrinsic muscles, enabling precise tongue movements essential for speech and swallowing. The palatoglossus muscle, by contrast, is innervated by the vagus nerve and is not supplied by the hypoglossal nerves.

Anatomy and course: The hypoglossal nerves originate from the hypoglossal nucleus in the medulla oblongata. They exit the brainstem as rootlets between the pyramid and olive, travel through the premedullary cistern, and enter the skull via the hypoglossal canal in the occipital bone. After exiting the skull, the nerves descend in the neck and then move toward the tongue, typically passing close to the hyoglossus muscle and distributing branches to the intrinsic muscles and most of the extrinsic muscles of the tongue.

Function: The hypoglossi provide motor innervation to the tongue’s muscles, coordinating movements required for articulation, shaping of the tongue during swallowing, and maintaining the delicate control of the tongue’s posture.

Clinical significance: Lesions of the hypoglossal nerves produce ipsilateral tongue weakness, atrophy, and fasciculations. On tongue protrusion, the tongue deviates toward the side of the lesion due to unopposed action of the contralateral genioglossus. Causes include brainstem or skull base stroke, tumor, trauma, or iatrogenic injury. Diagnosis relies on neurologic examination and imaging, with management directed at the underlying cause.

Etymology and naming: The term derives from hypo- “under” and glossus “tongue,” with the plural form hypoglossi used in some anatomical texts to refer to the pair of hypoglossal nerves.