The acoustic reflex is an involuntary muscle contraction that occurs in the middle ear of mammals in response to loud sound stimuli.
When presented with a loud sound stimulus, the stapedius and tensor tympani muscles of the ossicles contract. The stapedius pulls the stapes (stirrup) of the middle ear away from the oval window of the cochlea and the tensor tympani muscle pulls the malleus (hammer) away from ear drum. The reflex decreases the transmission of vibrational energy to the cochlea, where it is converted into electrical impulses to be processed by the brain. The acoustic reflex normally only occurs at relatively loud sound levels; activation for quieter sounds can indicate ear disfunction and absence of acoustic reflex can indicate neural hearing loss.
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