Download Lecture Organization A few words about sound

Introduction to the Auditory
Periphery.
Basic Cochlear Mechanics
Stavros Hatzopoulos Ph.D.
Lecture 1: Cochlear Mechanics for Audiologists
Lecture Organization
• Why bother with cochlear function
and cochlear mechanics.
• Basic concepts on how the ear
encodes the incoming sounds.
4 Basic
cochlear Macro-mechanics.
4 Basic
cochlear Micro-mechanics
• Concept: The healthy ear is NON linear
Stavros Hatzopoulos Ph.D.
Lecture 1: Cochlear Mechanics for Audiologists
A few words about
sound
Stavros Hatzopoulos Ph.D.
Lecture 1: Cochlear Mechanics for Audiologists
1
Acoustic Waves or SOUNDS
The Sound Transmission
Stavros Hatzopoulos Ph.D.
Lecture 1: Cochlear Mechanics for Audiologists
Acoustic Waves or SOUNDS
High
Frequency
Low Frequency
Stavros Hatzopoulos Ph.D.
Lecture 1: Cochlear Mechanics for Audiologists
Example of a graph showing the human voice
Stavros Hatzopoulos Ph.D.
Lecture 1: Cochlear Mechanics for Audiologists
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Structures of the
Auditory System
Stavros Hatzopoulos Ph.D.
Lecture 1: Cochlear Mechanics for Audiologists
The AuditorySystem
© Video Copyright Inserm 2002
Stavros Hatzopoulos Ph.D.
Lecture 1: Cochlear Mechanics for Audiologists
The periphery
© Video copyright Oticon 2001
Stavros Hatzopoulos Ph.D.
Lecture 1: Cochlear Mechanics for Audiologists
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The evolution of cochlear
mechanics
Stavros Hatzopoulos Ph.D.
Lecture 1: Cochlear Mechanics for Audiologists
Before the 1800s
• The first studies were primarily anatomical and
they identified the major features of the
auditory periphery (eardrum, middle-ear ossicles,
cochlea)
• The coiled BM was described by Du Verney
(1683)
• Reissner (1851), Corti (1851) and Deiters (1860)
applied new technologies and discovered
structures which were named after them.
Stavros Hatzopoulos Ph.D.
Lecture 1: Cochlear Mechanics for Audiologists
Stavros Hatzopoulos Ph.D.
Lecture 1: Cochlear Mechanics for Audiologists
4
Helmholtz- 1863
In 1863 Helmholtz suggests to the scientific
community that the frequency selectivity of the
cochlea can be explained by a bank of
INDEPENDENT and cascaded resonators (filters),
formed by the neural fibers.
Although his hypothesis is appropriate for an
introduction to cochlear mechanics, in essence
he was wrong, because he neglected the fluid
coupled BM segments.
Stavros Hatzopoulos Ph.D.
Lecture 1: Cochlear Mechanics for Audiologists
Georg von Békésy
• In his pioneering work from 1924 to 1960 ,
Georg von Bék ésy used new micro-dissection
techniques , a light microscope and
stroboscopic illumination to observe the
propagation of sound stimulation in cadaver
cochleas.
• He coined the sound propagation profile as the
TRAVELLING wave.
• He was the first to observe that different
frequencies were mapped at different “lengths”
of the Basilar membrane, coining the term
tonotopicity .
Stavros Hatzopoulos Ph.D.
Lecture 1: Cochlear Mechanics for Audiologists
Georg von Békésy
Stavros Hatzopoulos Ph.D.
Lecture 1: Cochlear Mechanics for Audiologists
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Cochlear Tonotopicity
© Copyright Inserm 2002
Stavros Hatzopoulos Ph.D.
Lecture 1: Cochlear Mechanics for Audiologists
The Travelling Wave
mechanics
a step by step tutorial
Stavros Hatzopoulos Ph.D.
Lecture 1: Cochlear Mechanics for Audiologists
INSIDE the cochlea there is
NO SOUND !!.
The acoustical vibrations arriving
at the stapes are being
transformed into a pressure wave
(TW) which moves from
10 -100 times
MORE SLOWLY than sound !!
Stavros Hatzopoulos Ph.D.
Lecture 1: Cochlear Mechanics for Audiologists
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External + Internal Views
Stavros Hatzopoulos Ph.D.
Lecture 1: Cochlear Mechanics for Audiologists
Inside the Cochlea
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Lecture 1: Cochlear Mechanics for Audiologists
The organ of Corti
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Lecture 1: Cochlear Mechanics for Audiologists
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The site of sound encoding
4,000 IHCs
12,000 OHCs
Stavros Hatzopoulos Ph.D.
Lecture 1: Cochlear Mechanics for Audiologists
The Travelling Wave mechanism
gives the ear the possibility to
project onto
its sensory epithelium a detailed
spatial image of the incoming
acoustical stimulation.
Stavros Hatzopoulos Ph.D.
The TravelingWave
Lecture 1: Cochlear Mechanics for Audiologists
Note:
At the peak
the BM displacement is
a FRACTION of
a nm !!!!
© Video Copyright Oticon 2001
Stavros Hatzopoulos Ph.D.
Lecture 1: Cochlear Mechanics for Audiologists
8
Advantages of using a TW
• The distribution of the stimulus energy in a
tonotopical manner (by frequency) relieves
the auditory nerve fibers of conveying
themselves the sound vibration. To recall
that the fibers transduce badly frequency
changes above 500 Hz !!
Stavros Hatzopoulos Ph.D.
Lecture 1: Cochlear Mechanics for Audiologists
Advantages of using a TW
• The TW is the means to achieve the sharp
localization and focusing of the incoming sound
vibrations. Such an action offers:
4 Enhanced
detection sensitivity .
immunity, therefore greater frequency
selectivity.
4 Reduction of the bulk of information which are
processed by the inner hair cells and the neural
fibers.
4 Greater noise
Stavros Hatzopoulos Ph.D.
Lecture 1: Cochlear Mechanics for Audiologists
Background INFO
4The vibration of the cochlea is induced by
pressure forces within the scalae , which
give rise to the notion of a Travelling Wave
(TW) .
4The first attempts to explain this behavior ,
by von Békésy, considered the travelling wave
as a passive phenomenon.
Stavros Hatzopoulos Ph.D.
Lecture 1: Cochlear Mechanics for Audiologists
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Origin of the
Place-Frequency map
4The cochlea is characterized by a grading of
partition STIFFNESS from base to the apex. This
fact generates the known cochlear
TONOTOPICITY.
Stavros Hatzopoulos Ph.D.
Lecture 1: Cochlear Mechanics for Audiologists
The Travelling Wave
Nobili, AshMore
and Mamano
Neuroscience
1998
Stavros Hatzopoulos Ph.D.
Lecture 1: Cochlear Mechanics for Audiologists
TW Background INFO
•
•
The TW grows in amplitude,
comes to a maximum, and
then declines sharply.
This is the result of the
difference in STIFFNESS,
MASS and WIDTH along the
basilar membrane.
Stavros Hatzopoulos Ph.D.
Lecture 1: Cochlear Mechanics for Audiologists
10
Cochlear Mechanics
step by step
Stavros Hatzopoulos Ph.D.
Lecture 1: Cochlear Mechanics for Audiologists
The Travelling Wave Generation
• The reason that the TW amplitude increases moving
from the base to the Apex, is the reduction in the wave
propagation speed.
• WHY IS THIS HAPPENING ? Because the basilar
membrane becomes more compliant (less stiff) and wider
with the distance from the stapes.
• As the TW slows down (its speed declines) the energy it
carries is being concentrated in a smaller distance.
Therefore the amplitude of the vibration increases .
Stavros Hatzopoulos Ph.D.
Lecture 1: Cochlear Mechanics for Audiologists
As a consequenceof the increase in the
amplitude of the vibration the velocities of the
“up” and “down” motion increase.
•
• The increase in motion implies an increase
in the viscous drag (friction) and the energy
losses.
•
As we move towards the point of
resonance the energy losses due to friction
increase. The point where the energy losses
equal the energy gain corresponds to the peak
of the TW .
Stavros Hatzopoulos Ph.D.
Lecture 1: Cochlear Mechanics for Audiologists
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Basic Cochlear
Macro--Mechanics
Macro
Stavros Hatzopoulos Ph.D.
Lecture 1: Cochlear Mechanics for Audiologists
Cochlear Micromechanics
• At the end of the 80s and the beginning of the
90s research was shifted to the understanding of
the active components in the cochlear sound
processing.
• Brownell (1982, 1985), Flock (1988, 1990), Evans
(1986) and later Ruggero and Rich (1992) have
shown that the OHCs are the ACTIVE
components responsible for the responsiveness
of the BM vibration.
Stavros Hatzopoulos Ph.D.
Lecture 1: Cochlear Mechanics for Audiologists
Cochlear Micromechanics
• The motile features of the OHCs are enhancing
the motion of the Basilar Membrane at their
characteristic frequency , which results in a
“better perception ” of that frequency.
• It was realized in the early 90s that OAEs can
help us understand the functioning of the
cochlear processing (or cochlear amplifier-a
term coined by Davis in 1983)
Stavros Hatzopoulos Ph.D.
Lecture 1: Cochlear Mechanics for Audiologists
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Stavros Hatzopoulos Ph.D.
Lecture 1: Cochlear Mechanics for Audiologists
Cochlear Mechanics: Summary of events
1. Vibration of the Basilar Membrane and bending
of the OHC and IHC stereocilia.
2. Transduction into cellular receptor potentials.
3. Generation of length changes in the OHCs.
4. Mechanical feedback of these changes on the
BM and TM.
5. Enhancement of the TW peak.
Stavros Hatzopoulos Ph.D.
Lecture 1: Cochlear Mechanics for Audiologists
Cochlear micro
micro--mechanics: A synopsis
1. Polarization = OHCs shrink and
BM moves upwards
2. Hyperpolarization = OHCs
expand and BM moves downwards
Cochlear Mechanics
© Video Copyright Promenade ‘round the cochlea
Stavros Hatzopoulos Ph.D.
Lecture 1: Cochlear Mechanics for Audiologists
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The CLEAR advantage Active vs
passive mechanics
© Copyright Promenade ‘round the cochlea
Stavros Hatzopoulos Ph.D.
Lecture 1: Cochlear Mechanics for Audiologists
OHC motility
recordings in-vitro
Stavros Hatzopoulos Ph.D.
Lecture 1: Cochlear Mechanics for Audiologists
Motility of
the
OHCs
Case A:
©Video Copyright
Joe Santos-Sacchi
ComplexStimulus (music)
Stavros Hatzopoulos Ph.D.
Lecture 1: Cochlear Mechanics for Audiologists
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Motility of
the
OHCs
Case B:
SimpleStimulus ( 1 kHz tone)
© Copyright
J. Ashmore 1999
Stavros Hatzopoulos Ph.D.
Lecture 1: Cochlear Mechanics for Audiologists
Motility of the OHCs
Free Field
© Copyright Holley and Ashmore 1988
Stavros Hatzopoulos Ph.D.
Lecture 1: Cochlear Mechanics for Audiologists
From Mechanics to
Hearing Science
Stavros Hatzopoulos Ph.D.
Lecture 1: Cochlear Mechanics for Audiologists
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Locating SNHL deficits
Stavros Hatzopoulos Ph.D.
Lecture 1: Cochlear Mechanics for Audiologists
Simulation of Noise Effects
1
2
3
© Copyright Inserm 2002
Stavros Hatzopoulos Ph.D.
Lecture 1: Cochlear Mechanics for Audiologists
Ototoxicity Effects
Cisplatin
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Lecture 1: Cochlear Mechanics for Audiologists
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Stavros Hatzopoulos Ph.D.
Lecture 1: Cochlear Mechanics for Audiologists
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