Stapedius
Ear · Head & Neck
The stapedius is the smallest skeletal muscle in the human body, housed entirely within the middle ear. It arises from the interior of the pyramidal eminence on the posterior wall of the tympanic cavity and its tiny tendon emerges to insert on the neck of the stapes, the innermost of the three auditory ossicles. When it contracts it tilts the stapes and dampens excessive vibration of the ossicular chain, protecting the delicate inner ear from loud sounds as part of the acoustic (attenuation) reflex. It is supplied by the nerve to stapedius, a branch of the facial nerve (CN VII). Because the facial nerve gives off this branch within the facial canal, a facial nerve lesion proximal to it causes hyperacusis, an uncomfortable sensitivity to loud sound.
Origin, Insertion, Action & Nerve
Origin
Apex of the pyramidal eminence on the posterior wall of the tympanic cavity
Insertion
Neck of the stapes
Action
Dampens excessive vibration of the stapes; protects the inner ear from loud sounds
Nerve
Nerve to stapedius (branch of facial nerve, CN VII)
Attachments explained
The Stapedius is defined first by where it attaches. Its origin is the more fixed anchor, usually the proximal or more stable end that stays put during contraction, while its insertion is the more mobile point that is pulled toward the origin when the muscle shortens.
Origin
Apex of the pyramidal eminence on the posterior wall of the tympanic cavity
Insertion
Neck of the stapes
Action & function
When the Stapedius contracts, it produces the following movements: Dampens excessive vibration of the stapes; protects the inner ear from loud sounds.
As part of the Ear group of the Head & Neck, it works alongside neighbouring muscles to generate smooth, coordinated movement and to stabilise the structures it acts on.
Nerve supply & clinical relevance
The Stapedius receives its nerve supply from the Nerve to stapedius (branch of facial nerve, CN VII).
Because a muscle can only contract when its nerve is intact, injury to the Nerve to stapedius can weaken or paralyse the Stapedius, impairing the movements it normally produces (dampens excessive vibration of the stapes). This is why knowing the innervation is central to localising nerve lesions in clinical practice.
How to study the Stapedius (the OIANS method)
Study the stapedius as one half of the middle ear's protective duo, paired with tensor tympani. Fix its action by its insertion on the neck of the stapes: pulling on the stapes stiffens the ossicular chain and blunts loud vibrations, which is why it protects the cochlea. Remembering that it is the smallest muscle in the body and that it acts on the smallest bone helps cement both the muscle and its target.
The high-yield point is the nerve and its clinical consequence. Stapedius is supplied by a branch of the facial nerve (CN VII) given off inside the facial canal, so a facial nerve palsy proximal to that branch produces hyperacusis. Pair this deliberately with tensor tympani, which is supplied by the mandibular nerve (CN V3), so you can immediately state which cranial nerve fails when each protective reflex is lost.
Frequently asked questions
Where is the Stapedius located?
The Stapedius is a muscle of the Ear group, located in the Head & Neck.
What is the origin of the Stapedius?
Apex of the pyramidal eminence on the posterior wall of the tympanic cavity
What is the insertion of the Stapedius?
Neck of the stapes
What movements does the Stapedius produce?
Dampens excessive vibration of the stapes; protects the inner ear from loud sounds
What nerve supplies the Stapedius?
Nerve to stapedius (branch of facial nerve, CN VII)
Is the Stapedius free to study in OIANS?
The Stapedius is always free to browse. Its full origin, insertion, action and nerve details are open to everyone in the Muscle Directory. Quiz and Flashcard practice for the Head & Neck is part of the one-time Lifetime upgrade, though; only the Upper Limb decks are free to test yourself on.
Related muscles
Study the Stapedius
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