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Noise Pollution
Published in Mary K. Theodore, Louis Theodore, Introduction to Environmental Management, 2021
Mary K. Theodore, Louis Theodore
The ear has its own defense mechanism against noise—the acoustic reflex. However, this reflex has vital weak points in its defenses. First of all, the muscles within the middle ear can become fatigued and slow if overused. A person who works in an environment with high noise levels gradually loses the strength in these muscles and thus more noise will reach the inner ear. Secondly, these muscles can be affected by chemicals within the working environment. Finally, the acoustic reflex is an ear-to-brain-to-ear circuit that takes at least nine-thousandths (0.009) of a second to perform. Individuals with poor acoustic reflex are usually subjected to temporary hearing loss when they come in contact with a loud noise. Most of the hearing loss caused by noise occurs during the first hour of exposure. Recovery of hearing can be complete several hours after the noise stops. The period of recovery depends upon individual variation and the level of noise that caused the deafness.
Hearing, Proprioception, and the Chemical Senses
Published in Robert W. Proctor, Van Zandt Trisha, Human Factors in Simple and Complex Systems, 2018
Robert W. Proctor, Van Zandt Trisha
Finally, the middle ear contains small muscles connected to the eardrum and to the stapes, which together produce the acoustic reflex in the presence of loud sounds (Fletcher & Riopelle, 1960; Schlauch, 2004). This reflex reduces the sound vibrations sent from the outer ear to the inner ear by making the eardrum and ossicles difficult to move; thus, the inner ear is protected from potentially damaging sounds. For people with intact middle ear structures and normal hearing, the acoustic reflex kicks in for sounds of about 85 decibels (Olsen, Rasmussen, Nielsen, & Borgkvist, 1999), but this will differ from person to person. The acoustic reflex requires about 20 ms to stabilize the ossicles, and it attenuates primarily low-frequency sounds. Thus, the reflex does not provide protection from sound with rapid onset (e.g., a gunshot) or from intense high-frequency sounds.
Noninvasive Tests Involving the Input of Audible Sound Energy
Published in Robert B. Northrop, Non-Invasive Instrumentation and Measurement in Medical Diagnosis, 2017
The auditory canal and eardrum can be modeled by a cylinder closed at its far end by a compliant (elastic) membrane, the eardrum. The degree of eardrum compliance is affected by two significant factors: (1) The difference in mean air pressure between the auditory canal (atmospheric pressure) and the air pressure in the middle ear. (2) The mechanical loading on the eardrum imposed by the ossicles and the oval window (cf. the discussion in Section 13.1). The point of maximum compliance of the eardrum occurs in the absence of loud sound when the air pressure in the auditory canal equals the air pressure in the middle ear. If at the point of maximum eardrum compliance, the contralateral ear is stimulated by a loud, broadband sound, the reflex contraction which occurs in the muscles of the middle ear causes a stiffening of the tympanic membrane and a consequent increase in the auditory impedance measured in the ipsilateral ear. Or, in other words, the auditory reflex causes a decrease in the compliance of the eardrum and a ∼30dB attenuation of sound coupled to the oval window. Measurement of the nonsubjective acoustic reflex by sensing small changes in the acoustic input impedance (or admittance) of the ear canal and eardrum has diagnostic significance in both hearing and neurological problems.
Evaluation of potential health effects associated with occupational and environmental exposure to styrene – an update
Published in Journal of Toxicology and Environmental Health, Part B, 2019
M.I. Banton, J.S. Bus, J.J. Collins, E. Delzell, H.-P. Gelbke, J.E. Kester, M.M. Moore, R. Waites, S.S. Sarang
Campo, Maguin, and Lataye (2007) investigated the underlying mechanism for the synergistic effects on hearing of a simultaneous exposure to noise and aromatic solvents, including styrene. After intravenous administration, it was found that the solvents can inhibit the protective middle and inner ear acoustic reflexes of the middle ear muscles. This acoustic reflex is elicited by intense sounds and serves to prevent cochlear damage by diminishing the penetration of high acoustic energies into the inner ear.