Nowadays OAE have a special role in electrophysiological examinations and also remarkable application in infants&apos hearing screening test. In the current article we have focused attention on the physiological fundamentals of OAE and tried to explain the trends in physiological studies that finally led to discovering the acoustic radiations by "David Kemp". By studying this article we can conclude that inner ear cannot be pondered just as a transformer that change the movements of the inner ear&aposs fluid to the neural signal, rather it should be considered as an active organ that can produce energy and also control the other active mechanisms involved in hearing.

Recent studies have demonstrated that outer hair cells play two functional roles in the ear: one is the sensory function and the other is motor one. The function of OHCs in being trigered with very poor signals can not be overlooked. This mechanism would lead in improving the sensitivity of the ear. As stimulus intensity increases, little by little, OHC will reach its saturation level and finally the amplification effect decreases.Otoacoustic emissions could be reverberations produced by the responses of outer hair cells .Any decrease in the number of OHCs can cause a mechanical split in the fine tuning mechanism of the organ of corti and result in hearing loss.

We expect some people benefit more from their hearing aids, but after a while they complain of inappropriate loudness growth.  Currently fitting hearing aids based on their loudness growth curves one of the best and most acceptable ways of fitting hearing aids we should study this curve based on the disturbed function of inner and outer hair cells. We should also know that based on which curves can make the growth curve of the damaged cells to normal ones.

Background and Aim: N-acetylcysteine, a glutathione precursor and reactive oxygen species scavenger, is reported to be effective in reducing noise-induced hearing loss. Many workers in industry are exposed simultaneously to noise and chemical pollutants such as carbon monoxide. We investigated effectiveness of N-acetylcysteine in protecting the cochlea from simultaneous noise and carbon monoxide damages.
Methods: Twelve rabbits were exposed simeltaneously to 100 dB sound pressure level of broad band noise and carbon monoxide 8 hours a day for 5 days. One hour before exposure, experimental group received 325 mg/kg of N-acetylcysteine while normal saline was administered for the control group. The protective effect of N-acetylcysteine was evaluated 3 weeks after exposure by histological assessment of the hair cells.
Results: Simultaneous exposure to noise and carbon monoxide resulted in a considerable damage to the outer hair cells however, the inner hair cells and the pillar cells remained intact. Use of N-acetylcysteine in the experimental group significantly reduced the extent of outer hair cell loss.
Conclusion: N-acetylcysteine attenuates simultaneous noise and carbon monoxide induced hair cell damage in rabbits.
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