Physiology of Hearing

Physiology of Hearing


PHYSIOLOGY OF HEARING

Conduction of sound

  • Impedance matching mechanism or Transformer action of middle ear: conversion of sound of greater amplitude with lesser force to that of lesser amplitude but greater force
  • It is accomplished by
  • vLever action of ossicles
  • Handle of malleus is 1.3 times longer than the long process of incur
  • Mechanical advantage  = 1.3
  • Lever ratio = 1.3 : 1

Hydraulic action of TM

  • Effective vibratory area of TM = 55 sq.mm.
  • Area of Foot Plate of stapes = 3.2 sq.mm.
  • Hydraulic ratio  = 17: 1
  • The product of Lever ratio and Hydraulic ratio (17 x 1.3) gives the Transformer ratio of 22: 1

Natural resonance and efficiency of auditory apparatus

  • External auditory canal  — 3000 Hz
  • Tympanic membrane — 800 to 1600 Hz
  • Middle ear  — 800 Hz
  • Ossicular chain — 500 to 2000 Hz

Intensity of various sound at a distance of 1 m

  • Whisper — 30 dB
  • Normal conversation  — 60 dB
  • Shout  — 90 dB
  • Discomfort of the ear  — 120 dB
  • Pain in the ear  — 130 dB

?    Frequency range in normal hearing — 20 Hz to 20000 Hz
?    In routine audiometric testing — 125 to 8000 Hz are evaluated

Exam Question
 

PHYSIOLOGY OF HEARING

Conduction of sound

  • Impedance matching mechanism or Transformer action of middle ear: conversion of sound of greater amplitude with lesser force to that of lesser amplitude but greater force
  • It is accomplished by
  • Lever action of ossicles
  • Handle of malleus is 1.3 times longer than the long process of incur
  • Mechanical advantage     = 1.3
  • Lever ratio    = 1.3 : 1

Hydraulic action of TM

  • Effective vibratory area of TM     = 55 sq.mm.
  • Area of Foot Plate of stapes    = 3.2 sq.mm.
  • Hydraulic ratio    = 17: 1
  • The product of Lever ratio and Hydraulic ratio (17 x 1.3) gives the Transformer ratio of 22: 1

Natural resonance and efficiency of auditory apparatus

  • External auditory canal — 3000 Hz
  • Tympanic membrane  — 800 to 1600 Hz
  • Middle ear  — 800 Hz
  • Ossicular chain  — 500 to 2000 Hz

Intensity of various sound at a distance of 1 m

  • Whisper  — 30 dB
  • Normal conversation  — 60 dB
  • Shout  — 90 dB
  • Discomfort of the ear   — 120 dB
  • Pain in the ear  — 130 dB

?    Frequency range in normal hearing — 20 Hz to 20000 Hz

?    In routine audiometric testing — 125 to 8000 Hz are evaluated

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