Nerve to Geniohyoid

nervus musculi geniohyoidei

The nerve to the geniohyoid is carried by the hypoglossal nerve (CN XII) but actually derives its motor fibres from the C1 anterior ramus, which hooks around the hypoglossal nerve and uses it as a conduit to reach the geniohyoid muscle. It branches from the hypoglossal nerve in the floor of the mouth to enter the deep surface of geniohyoid. This C1 ventral ramus contribution also provides the descending root of the ansa cervicalis.

Region: Neck

Clinical Relevance

Clinical Notes

The nerve to geniohyoid and its C1 origin is relevant in understanding ansa cervicalis anatomy and in explaining why some muscles supplied by C1 via CN XII are not classically 'hypoglossal' muscles. In floor of mouth surgery and radical neck dissection that divides CN XII, all geniohyoid motor function is lost on the affected side. C1 spinal cord injuries may specifically spare the hypoglossal-carried C1 branches to geniohyoid since these enter the ansa cervicalis at the carotid sheath level rather than passing through the foramen magnum.

Pathology

Common Injuries & Conditions

Geniohyoid Paralysis After CN XII Injury

Hypoglossal nerve injury from neck dissection, endarterectomy, or skull base trauma paralyses the geniohyoid via its C1 fibres carried by CN XII, impairing the active hyoid elevation required for swallowing and contributing to post-operative dysphagia alongside the tongue motor deficit.