Middle-ear muscles automatically stiffen to block loud sounds

Evidence

The second function of the middle ear is to provide some protection for the hearing system from the effects of loud sounds, whether from external sources or the individual concerned. This occurs as a result of the action of two muscles in the middle ear: the tensor tympani and the stapedius muscle. These muscles contract automatically in response to sounds with levels greater than approximately 75 dB(SPL), and they have the effect of increasing the impedance of the middle ear by stiffening the ossicular chain. This reduces the efficiency with which vibrations are transmitted from the tympanic membrane to the inner ear and thus protects the inner ear to some extent from loud sounds. Approximately 12 to 14 dB of attenuation is provided by this protection mechanism, but this is for frequencies below 1 kHz only. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 541

Categorization

• DEFINE: Explains the mechanical mechanism of the acoustic reflex and the specific roles of tensor tympani and stapedius.
• XREF: Connects to the noise-exposure and fight-or-flight material from One Square Inch of Silence — the body’s built-in defense against loud sound. — connects to: An acoustic reflex desensitizes the ear to protect cochlear hair cells; SOAE bouncing is not caused by middle-ear impedance changes; Otosclerosis stiffens ossicle movement and attenuates transmitted sound (+2 more)
• corroborated: 2 independent passages support this claim — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 541