Chapter 6: The Outer and Middle Ears

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Chapter 6 The Outer andMiddle Ears
This Power Point Presentation is to accompany the
textbook FUNDAMENTALS OF HEARING AN
INTRODUCTION (5th Edition) Published by Elsevier
Press and authored by William A. Yost. Please
consult the Power Point Instructions at this Web
Site before using this Presentation.
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The Peripheral Auditory System
Outer (External) Ear Directs sound to the
middle ear, amplifies or attenuates sound in
frequency specific manner depending on relative
location of the sound source.
Middle Ear Matches the impedance difference
between air and the fluids/tissues of the inner
ear direct stimulation of the inner ear
protection
Inner Ear Transduction of sound/ vibration into
the neural code for sound
Auditory Nerve Transmits neural code for sound
to the brainstem and cortex
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The Anatomy of the Outer Ear
1. Pinna
2. External auditory canal
3. Tympanic membrane (ear drum)
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4. Concha
5. External auditory meatus
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The Anatomy of the Middle Ear
Epitympanum
External Ear Canal
Round widow
Eustachian tube
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The Ossicular Chain
1 Manubrium 2 MALLEUS 3 Head of Malleus 4
INCUS 5 Short Process 6 Long Process 7
STAPES 8 Cura 9 Stapes Footplate
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2
5
4
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1
8
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8
9
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Head Related Transfer Function (HRTF)
At Loudspeaker
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Concha and Ear Canal Transfer Function
Standing Waves
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Middle Ear Transfer Function
Difference between Tympanic Membrane (red
measurement point) and Fluids of Inner Ear
(brown measurement point)
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Normal Function of Middle Inner Ear
MIDDLE EAR
OUTER EAR
INNER EAR
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Problem 1 Impedance Mismatch
MIDDLE EAR
OUTER EAR
INNER EAR
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Problem 2 Round and Oval Widowsboth stimulated
in same direction
MIDDLE EAR
OUTER EAR
INNER EAR
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Problem 3 Middle Ear Cavitycannot be closed
MIDDLE EAR
OUTER EAR
INNER EAR
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Ossicular Chain solves Problems 1 2
MIDDLE EAR
OUTER EAR
INNER EAR
MALLEUS, INCUS, STAPES
EUSTACHIAN TUBE
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Eustachian Tube solves Problem 3
MIDDLE EAR
OUTER EAR
INNER EAR
EUSTACHIAN TUBE
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Impedance Match Provided by Ossicular Chain
Middle Ear
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Pressure Ratio (Manubrium to Stapes Footplate)
20Log(17)25 dB
17 to 1
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1.3 to 1
20Log(1.3)2 dB
Lever Action (Ossicular Chain)
2 to 1
Buckling (Tympanic Membrane)
20Log(2)6 dB
TOTAL GAIN 33 dB
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Function of the Tympanic Membrane and Ossicular
Chain
Tympanic Membrane White
Grid Malleus Red Incus Green Stapes Blue
(Left), Yellow (Right)