• the cochlear duct prism (vicase’s prism) does not resolve the frequencies very finely

  • it does not gather a lot of intensity

  • the audio heard by a live human is far louder and the frequency resolution is much higher than the physical cochlear duct prism obtained from a cadaver

outer hair cell mobility

  • cochlear duct has cilia (hair cells) that converts fluid waves to electrical signals

two types

  • inner hair cells
    • proper sensory neurons
    • sensory information received is sent the brain
    • via the vestibulo-cochlear nerve fibers
  • outer hair cells
    • not proper sensory neurons
    • they respond to sound, but do not project to the brain
  • brain only receives signals from inner hair cells

amplification

  • there are three times more outer hair cells than inner hair cells
    • they are responsible for cochlear amplification
    • the outer hair cells physically move
    • to enable hearing transduction into the inner hair cell sensory neurons
  • when the cell is exposed to fluid wave in the cochlear fluid enclosure
    • the cells move back and forth
    • causing them to expand and contract with the wave
  • the cells are motile
    • prestin resides at the membrane of the cell connection to the walls of the cochlear prism
  • resonant frequency of any structure at which the frequency amplifies
    • wine glass shattering at high pitches in operas
    • car doors vibrate at particular base frequencies way more than others
    • windows vibrate when a plane flies over at a particular frequency
    • bridges sometimes vibrate due to wind and collapse at their resonant frequency
  • prestin makes the membrane wall move up and down only at the place where it matches the resonant of the cochlea
    • resonant frequencies are narrow ranges
    • this solves two problems:
      • increases the signal strength for the inner cilia
      • improves the gross prism’s frequency resolution
  • sound is amplified in the external ear
    • some of the intensity that is lost in the middle ear
    • is gained in the cochlear amplifier

oto-acoustic emissions

  • when the outer hair cells move when activated
    • this moves the cochlear canal prism membrane
    • which produces as wave that goes backwards
  • these waves are called otoacoustic emissions
    • can be picked up by a physician’s mic in the ear canal
    • useful for checking if everything until the cone is healthy
      • especially in babies and other non-verbal individuals