Stapedius muscle

The stapedius is the smallest skeletal muscle in the human body. At just over one millimeter in length, its purpose is to stabilize the smallest bone in the body, the stapes.

The stapedius emerges from a pinpoint foramen in the apex of the pyramidal eminence (a hollow, cone-shaped prominence in the posterior wall of the tympanic cavity), and inserts into the neck of the stapes.

Function

It reflexively dampens the vibrations of the stapes by pulling on the neck of that bone. It prevents excess movement by the stapes, helping to control the amplitude of sound waves from the general external environment to the inner ear. The stapedius muscle dampens the ability of the stapes vibration and protects the inner ear from high noise levels, primarily the volume of your own voice. Compare also the role of the tensor tympani muscle, which primarily dampens those sounds associated with chewing.

Innervation

The stapedius is innervated by the nerve to stapedius, a branch of cranial nerve VII, the facial nerve. This is the first branch of the facial nerve after it exits the facial canal; the second branch is the chorda tympani which carries special sense (taste) and parasympathetic fibres of cranial nerve VII. It provides taste sensation to the anterior 2/3 of the tongue by joining with the lingual nerve - a branch of the Mandibular nerve (V3) - in the infratemporal fossa^[1].

Pathology

Paralysis of the stapedius, such as in Bell's palsy, allows wider oscillation of the stapes, resulting in heightened reaction of the auditory ossicles to sound vibration. This condition, known as hyperacusis, causes normal sounds to be perceived as very loud.

See also

• Acoustic reflex

References

External links

• 409665614 at GPnotebook
• LUC stap
• Stapedius+muscle at eMedicine Dictionary