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Middle Ear Functions

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Middle Ear Functions Impedance Matching -- amplification of sounds to overcome difference in impedance between the air of EAC and the fluid of the inner ear. – PowerPoint PPT presentation

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Title: Middle Ear Functions


1
Middle Ear Functions
  • Impedance Matching -- amplification of sounds to
    overcome difference in impedance between the air
    of EAC and the fluid of the inner ear.
  • Filtering -- resonant frequency is approximately
    1000 Hz, functions as bandpass filter.
  • Acoustic Reflex -- Contraction of Stapedius
    muscle in response to loud sounds

2
INNER EAR
  • Two Halves
  • Vestibular--transduces motion and pull of gravity
  • Cochlear--transduces sound energy
  • (Both use Hair Cells)

3
Subdivision into spaces containing endolymph
(blue), and spaces containing perilymph (red)
4
Cochlea is Divided into 3 Scala
  • Scala Vestibuli
  • Reissners Membrane
  • Scala Media
  • Basilar Membrane
  • Scala Tympani
  • Helicotrema - the opening between 2 outer Scala

5
Fluids filling the Inner Ear
  • Perilymph- in S. Vestibuli and S. Tympani
  • High Sodium / Low Potassium concentrations
  • Low Voltage (0 to 5 mV)
  • Endolymph- in S. Media
  • High Potassium / Low Sodium concentrations
  • High Positive Voltage (85 mV)

6
Cross-Section of the Cochlea
Third Turn
Second Turn
First Turn
7
(No Transcript)
8
A Cross Section Shows the 3 Scala
9
(No Transcript)
10
Within S. Media is the Organ of Corti
11
  • I Inner Hair Cells P Pillar Cells
  • O Outer Hair Cells D Deiters Cells

12
The Stereocilia on IHCs and OHCs
  • OHCs (at top)
  • V or W shaped ranks
  • IHC (at bottom)
  • straight line ranks

13
Cochlear Functions
  • Transduction- Converting acoustical-mechanical
    energy into electro-chemical energy.
  • Frequency Analysis-Breaking sound up into its
    component frequencies

14
Transduction-
  • Inner Hair Cells are the true sensory
    transducers, converting motion of stereocilia
    into neurotransmitter release.
  • Mechanical? Electro-chemical
  • Outer Hair Cells have both forward and reverse
    transduction--
  • Mechanical ? Electro-chemical
  • Mechanical? Electro-chemical

15
Frequency Analysis - the Traveling Wave
  • Bekesy studied cochleae from cadavers, developed
    the Traveling Wave theory
  • 1. Response always begins at the base
  • 2. Amplitude grows as it travels apically
  • 3. Reaches a peak at a point determined by
    frequency of the sound
  • 4. Vibration then dies out rapidly
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