Explain the mechanism of hearing in human being.

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MECHANISM OF HEARING IN HUMAN BEING OR

MECHANISM THROUGH WHICH A SOUND PRODUCES A NERVE IMPULSE IN THE INNER EAR

  • At the initial stage of hearing, it is observed that the sound is generally caused by the vibration of air molecules.
  • Here, the number of vibrations (waves/cycle) per second (Hz) correlates with the pitch of sound.
  • This shows that higher the frequency, higher the pitch of sound.
  • The range of the frequency of human audible spectrum is about 20 to 20,000 Hz.
  • The intensity of sound is expressed in decibel (dB), which correlates with amplitude of the sound waves.
  • The basic mechanism of hearing is as follows:
  1. Sound waves change the pressure that stimulates the movement of the tympanic membrane.
  2. This cause vibration of tympanic membrane.
  3. These vibrations of membrane are then transmitted to oval window via the ossicular chain.
  4. Due to this transmission, perilymph of scala vestibule vibrates that disturb reissner’s membrane.
  5. Now the waves enter endolymph in scala media that vibrates basilar membrane.
  6. Membrane around the window oscillates. This shows that when the movement of stapes goes inward, the membrane around the window moves outward.
  7. High pitched sound makes displacement of basilar membrane more close to the window.
  8. Simultaneously, high pitched sounds stimulate the nerve impulse in the corti, situated at the basal part of basilar membrane.
  9. The transmitted nerve impulse effect specific part of the auditory area.
  • 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.
  • The intensity of normal conversation sound is approximately 50dB and the intensity of the sound caused by heavy vehicles is 80 to 90dB.
  • 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:

  1. Image: http://www.ifd.mavt.ethz.ch/education/student_projects/edom_Hopf/Enz_Brit_Hearing_mechanism.gif?hires
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