Noise and Hearing
Location: Outside U.S.
Date: Spring 2012
Why does noise damage our hearing?
The principal mechanism for hearing loss due to noise, whether chronic or acute, is through damage to the stereocilia possessing sense cells of the cochlea in the inner ear compartment. The cochlea is a fluid filled organ that is lined with sensing cells possessing stereocilia(little hairs) that vibrate in response to sound. The cochlea is horn shaped so that the vibrations of the cilia reflect the frequency of the sound perceived.
Vibrating stereocilia are attached to the sensing cell which converts the vibrations to a neural signal and that impulse is sent on to the brain through cochlear nerve fibers.
The brain and sense cells are kept to the point of high sensitivity by a neural feedback loop. This set point of high sensitivity through feedback gives us amazing discriminatory and selectivity in our hearing. However, when small disturbances in the feedback loop occur, the result is feedback oscillation. We hear this oscillation as tinnitus(ringing in the ears). The oscillation is analogous to the squealing feedback one hears when a microphone is held too close to a loudspeaker.
Loud noise, if acute, causes temporary reactive oxygen damage to the sensing cells. This causes tinnitus, a perception of spatial fullness and deadened response in hearing. Extreme acute loud noise may lead to permanent damage.
Continued loud noise causes chronic reactive oxygen damage so that eventually the sensing cells are either killed or permanently distressed. This condition may lead
to continuous tinnitus, permanent deafness or both.
Living in the quiet zone,
Peter E. Hughes, Ph.D.
Loud noises injure the tiny hair cells in the cochlea which is part of the inner ear. When those tiny hairs cells get damaged, the frequency of sound those hairs sense cannot be heard or it takes a louder sound (higher amplitude) of that frequency to stimulate them. Unfortunately, once those structures are damaged, the hearing loss is permanent.
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Update: June 2012