MECHANISM OF HEARING IN HUMAN BEING OR
MECHANISM THROUGH WHICH A SOUND PRODUCES A NERVE IMPULSE IN THE INNER EAR
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At the initial stage of hearing, it is observed that the sound is generally caused by the vibration of air molecules.
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Here, the number of vibrations (waves/cycle) per second (Hz) correlates with the pitch of sound.
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This shows that higher the frequency, higher the pitch of sound.
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The range of the frequency of human audible spectrum is about 20 to 20,000 Hz.
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The intensity of sound is expressed in decibel (dB), which correlates with amplitude of the sound waves.
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The basic mechanism of hearing is as follows:
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Sound waves change the pressure that stimulates the movement of the tympanic membrane.
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This cause vibration of tympanic membrane.
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These vibrations of membrane are then transmitted to oval window via the ossicular chain.
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Due to this transmission, perilymph of scala vestibule vibrates that disturb reissner’s membrane.
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Now the waves enter endolymph in scala media that vibrates basilar membrane.
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Membrane around the window oscillates. This shows that when the movement of stapes goes inward, the membrane around the window moves outward.
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High pitched sound makes displacement of basilar membrane more close to the window.
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Simultaneously, high pitched sounds stimulate the nerve impulse in the corti, situated at the basal part of basilar membrane.
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The transmitted nerve impulse effect specific part of the auditory area.
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Now, if the elasticity of basilar membrane is lost, hearing of the high pitch sounds. This mostly happens at the old age that is known as presbycusis.
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The intensity of normal conversation sound is approximately 50dB and the intensity of the sound caused by heavy vehicles is 80 to 90dB.
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The range of 120 to 140 dB of the sound intensity, causes discomfort and pain, i.e. louder the sound, damages the hearing organ.
REFERENCE:
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Image: http://www.ifd.mavt.ethz.ch/education/student_projects/edom_Hopf/Enz_Brit_Hearing_mechanism.gif?hires
