stapediusact

Stapedius act, also referred to as the action of the stapedius muscle, describes the function of the stapedius in the middle ear and its role in the acoustic reflex. The stapedius is a tiny skeletal muscle that originates from the pyramidal eminence on the posterior wall of the tympanic cavity and inserts into the neck of the stapes (the stapedial or stirrup bone). It is the smallest striated muscle in humans.

The muscle is innervated by the nerve to stapedius, a branch of the facial nerve (cranial nerve VII). Upon activation, the stapedius contracts and pulls the head of the stapes posteriorly, tensing the tympanic cavity and reducing the amplitude of stapes vibration. This dampening effect decreases the efficiency of sound transmission to the inner ear, forming part of the acoustic reflex that protects the inner ear from potential damage caused by loud noises.

The stapedius reflex contributes to sound localization and helps regulate auditory sensitivity, particularly under high-intensity or sustained noise exposure. Clinically, dysfunction of stapedius muscle control—often due to facial nerve pathology—can lead to hyperacusis, a heightened sensitivity to everyday sounds. In audiology, testing for the stapedius reflex (acoustic reflex testing) provides information about middle-ear status and neural pathways involved in auditory processing.