stapediusreflexen

The stapedius reflex, also known as the acoustic reflex, is an involuntary contraction of the stapedius muscle in the middle ear. This muscle, attached to the stapes bone, is the smallest skeletal muscle in the human body. When exposed to loud sounds, the stapedius muscle contracts, which in turn stiffens the ossicular chain of the middle ear. This stiffening attenuates sound transmission to the inner ear, effectively reducing the amplitude of loud sounds reaching the cochlea and protecting it from potential damage.

The reflex is typically elicited by sounds above a certain intensity threshold, usually around 80-90 decibels (dB) Sound Pressure Level (SPL). The reflex can be triggered by sounds presented to either ear (ipsilateral reflex) or to the opposite ear (contralateral reflex), mediated by the brainstem. It is a bilateral reflex, meaning that a loud sound presented to one ear will cause the stapedius muscle to contract in both ears.

The stapedius reflex is a crucial protective mechanism against noise-induced hearing loss. It also plays a role in auditory adaptation, helping to dampen the perception of sustained loud noises. Assessment of the stapedius reflex is a common diagnostic tool in audiology, used to evaluate the integrity of the auditory pathway from the ear canal to the brainstem. Abnormalities in the reflex can indicate problems with the middle ear, facial nerve, or central auditory processing. For example, a complete absence of the reflex might suggest a conductive hearing loss, a stapedius muscle paralysis, or a lesion in the brainstem.