The stapedius is the smallest named muscle in the human body, measuring approximately 1 millimetre in length, housed in the pyramidal eminence of the middle ear. It tilts the stapes to stiffen the ossicular chain and reduce sound transmission to the inner ear, protecting the cochlea from loud sounds. Its absence from facial nerve palsy produces hyperacusis — painful hypersensitivity to normally tolerable sounds because the stapedial reflex is lost.
| Origin | Inside the pyramidal eminence of the posterior wall of the middle ear cavity |
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| Insertion | Posterior neck of the stapes |
| Nerve Supply | Facial nerve (CN VII) via the stapedial branch |
| Blood Supply | Stylomastoid artery |
| Actions | Tilts the stapes to dampen its vibration and reduce sound transmission to the cochlea; Protective reflex against loud sounds — contracts before and during loud sound production |
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The stapedial reflex protects the cochlea during loud sounds including a person's own voice and chewing sounds. Before speaking loudly the stapedius contracts anticipatorily to dampen the speaker's own voice transmission — a feedforward protective mechanism that is lost in facial nerve palsy, explaining why Bell palsy patients find their own voice unbearably loud.
Hyperacusis in Bell palsy from stapedius paralysis is assessed clinically and by audiometry measuring the stapedial reflex threshold — absent reflex confirms facial nerve lesion proximal to the stapedial nerve branch, helping localise the lesion within the facial canal. The stapedial reflex is routinely tested in audiometry as part of immittance testing to screen for facial nerve integrity and middle ear pathology.
Not accessible to palpation due to its location in the middle ear.
Stapedius denervation producing painful sound sensitivity from loss of the stapedial protective reflex, confirmed by absent stapedial reflex on audiometry and resolving as the facial nerve recovers.
