The ear

Label a diagram of the ear.

 

include:

pinna, eardrum, bones of middle ear, oval window, round window, semicircular canals, auditory nerve and cochlea.

 

7. Explain how sound is perceived by the ear, including the roles of the eardrum, bones of the middle ear, oval and round windows, and the hair cells of the cochlea.

 

1- eardrum

• sound waves cause eardrum to vibrate towards and away from middle ear
• eardrum transmits mechanical vibration of air molecules to middle ear

2- 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
    • by contracting to damp down vibrations
• amplify sound x20 by acting as levers:
  • reduce sound wave amplitude
  • increase sound wave force
  • oval window's small size relative to eardrum increases amplification

3- oval window:

• transmits sound waves to the fluid filling the cochlea
  • cochlea is a fluid-filled tube coiled into a spiral shape
    • fluid is incompressible
  • round window responds to movements in oval window
    • maintaining constant volume of fluid
  • fluid in cochlea vibrates in response to oval window vibrations

4- hair cells in cochlea:

• hair cells stretch from hair cell membrane to cochlear tube membrane
  • hair bundles vibrate in response to sound waves traveling through cochlear fluid
• each hair cell resonates in response to specific wavelengths of sound
  • due to gradual gradations in width and thickness of cochlear membrane
• when hair bundles vibrate, hair cells transmit action potentials
  • synapse with auditory nerve
  • travel to auditory cortex in brain