The geniohyoid is a narrow muscle running from the inner mandibular chin to the hyoid, acting as a short powerful suprahyoid elevator that pulls the hyoid anterosuperiorly during swallowing. It is innervated by C1 fibres hitchhiking along the hypoglossal nerve, making it a rare example of a muscle in the head and neck region not innervated by a cranial nerve. Its action shortens the floor of the mouth and contributes to hyoid elevation for airway protection.
| Origin | Inferior mental spine on the inner surface of the mandibular symphysis |
|---|---|
| Insertion | Body of the hyoid bone |
| Nerve Supply | Ventral ramus of C1 via the hypoglossal nerve (CN XII) — travels with CN XII but is C1 in origin |
| Blood Supply | Submental artery |
| Actions | Elevates and protracts the hyoid bone during swallowing; Depresses the mandible when the hyoid is fixed by the infrahyoids |
|---|
The short lever arm between the mandible and hyoid gives the geniohyoid a mechanical advantage for rapid hyoid elevation at the onset of swallowing, contributing to the high-speed laryngeal elevation needed to protect the airway during the pharyngeal phase.
Geniohyoid atrophy from C1 nerve root or hypoglossal nerve injury reduces hyoid elevation speed during swallowing, increasing aspiration risk particularly for thin liquids that require the fastest airway protection response. Assessment by videofluoroscopy comparing the speed of hyoid elevation between the two sides identifies geniohyoid dysfunction.
Not directly palpable as it lies deep to the mylohyoid in the floor of the mouth.
Reduced hyoid elevation speed from geniohyoid weakness causing thin liquid aspiration, identified by videofluoroscopy and managed with compensatory swallowing strategies.
