Stapedius

The stapedius is the smallest striated 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 is innervated by the tympanic branch of cranial nerve VII, the facial nerve.

Function
It prevents excess movement by the stapes, helping to control the amplitude of sound waves from the general external environment to the inner ear. (Compare the role of the tensor tympani muscle, which primarily dampens those sounds associated with chewing.)

Pathology
Paralysis of the stapedius 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.