The nerve to stapedius is a tiny motor branch of the facial nerve that arises in the vertical (mastoid) part of the facial canal, opposite the pyramidal eminence of the middle ear. It supplies stapedius, the smallest skeletal muscle in the body. Stapedius pulls on the stapes to damp its movement and protect the inner ear from loud sound.
| Origin | Facial nerve in the mastoid (descending) segment of the facial canal |
|---|---|
| Course | Passes forward through a small canal to reach stapedius, which lies inside the pyramidal eminence on the posterior wall of the middle ear |
| Motor | |
| Sensory |
|
When the facial nerve is damaged above the origin of this branch, the stapedius is paralysed and ordinary sounds can seem painfully loud on that side (hyperacusis). The stapedial (acoustic) reflex, measured with tympanometry equipment, tests this branch and helps localise facial nerve lesions and assess conductive hearing loss. Reflex absence on the side of a facial palsy suggests a lesion at or above the mastoid segment.
Facial nerve inflammation proximal to the nerve to stapedius paralyses stapedius, so normal sounds seem loud and uncomfortable in the affected ear. It usually settles as the facial palsy recovers.
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