HL 2 Biology

E.2c Ears

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How sound is perceived:

  • eardrum
    • vibrated by sound waves
    • transmits mechanical vibration of air molecules –> middle ear
  • bones of middle ear
    • ossicles = series of very small bones
      • 1st = attached to eardrum
      • 3rd = attached to oval window
      • muscles = attached to ossicles (protect from loud sound)
    • acts as lever to amplify sound x20:
      • reduce sound wave amplitude
      • increase sound wave force
      • oval window’s small size relative to eardrum increases amplification
  • oval window:
    • transmits sound waves to the fluid,  filling the cochlea
      • cochlea: fluid-filled tube coiled into a spiral shape
        • fluid = incompressible
      • round window responds to movements in oval window
        • maintaining constant volume of fluid
      • fluid in cochlea vibrates as oval window vibrates
  • hair cells in cochlea:
    • stretch from hair cell membrane –> cochlear tube membrane
      • hair bundles vibrate in response to sound waves going through cochlear fluid
    • resonates in response to specific wavelengths of sound
      • due to gradual gradations in width & thickness of cochlear membrane
    • when hair bundles vibrate, transmits action potentials
    • synapse with auditory nerve
    • travel to auditory cortex (brain)
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