Tongue movement

Key point

■ The nucleus of the hypoglossal nerve is located in the caudal medulla oblongata. Its fibres innervate the intrinsic and extrinsic muscles of the tongue.

The hypoglossal nucleus (CN XII) is located in the ventral medulla oblongata near the midline extending rostrally from the pyramidal decussation (A2, A3, A22-24, A28).

Efferent fibres exit the caudal medulla oblongata as a series of rootlets. The rootlets fuse and after emerging from the skull, the nerve becomes prominent due to the addition of connective tissue. It innervates the thyrohyoideus, geniohyoideus, styloglossus, hyoglossus, genioglossus muscles and the intrinsic muscles (m. propria linguae) of the tongue.

Being a LMN, loss of hypoglossal innervation results in atrophy of tongue muscles. In the early stages, a unilateral lesion will present as loss of tone on that side of the tongue, but chronically, due to loss of striated muscle fibres and subsequent fibrosis, the affected side will be shrunken and contracted causing deviation of the tongue (Fig. 10.21).

Fig. 10.21 Atrophy and contracture of the right side of the tongue secondary to loss of hypoglossal innervation

(courtesy of Mr. Robert Salwicki, IVABS, Massey University).