Passive (Macro) Mechanics / Cochlear Physiology Flashcards
T/F The auditory system is one of the most sensitive systems
True
How does the mechanical nature of the cochlear allow for discrimination of different sounds by the brain?
mechanical system is very sensitive; TM deflections are as small as 1/10 diameter of H atom causing hearing; BM movements may be 100 times smaller than this
- movement that small (BM –> action potential)
organ of corti review
basilar membrane changes in _________ through the cochlear spiral
width
narrow @ __________ end
basal end
wider @ ___________ end
apical; allows for more vibration
attachment point of the tectorial membrane is more __________ than the attachment of the basilar mebrane
medial
why does the attachment point of the tectorial membrane being more medial than attachment of the BM aid stereocilia deflection?
more effective shearing force across stereocilia
a wider BM will be less _______ than a narrow BM
stiff
the difference in _____________ creates a more effective shearing force across stereocilia
points of rotation
fluid motions of the scalae (vestibuli and tympani)
macromechanics
macromechanics assumes
that the cochlear duct or scala media is a flat cochlear partition and is a dynamic structure exhibiting characteristics of mass, stiffness, and damping
mass
weight, wider more cells
stiffness
flexibility, wider more flexible
damping
loss of vibrational energy due to viscosity of fluids and friction; doesnt play a large role in macromechanics
diagram of the cochlear partition
there is more ___________ at one location [either basal or apical end]
vibration
T/F We cannot use a physical model to show that stiffness and mass can affect resonant frequency
False; we can use a physical model to show that stiffness and mass can affect the resonant frequency
of frequency-specific stimuli and measure the resultant amplitude of the vibrations show…
a) frequnecy that peaks in peak amplitude = system’s resonant frequency (RF)
b) increasing stiffness = reduces amplitude of vibrations below resonant frquency and shifts the resonant frequency higher
physical model showing stiffness and mass can affect RF
Helmholtz described the cochlea as a ______________, each tuned to diff frequency and occupying diff location on the BM
bank of highly tuned resonators
what did Helmholtz fail to explain
the coupling mechanism between middle and inner ears - cochlear fluids
Von Bekesy was the first to demonstrate the _______________ behavior of the BM
traveling wave
Von Bekesy used human cadavers and assumed the BM functioned similar to ______________ membrane
Reissner’s
diagram of the traveling wave
Von Bekesy also saw the first observation of _________________
tonotopic organization
Von Bekesy observed that the cochlear is like a _____________ system in which a “traveling wave” is transmitted along the length of the cochlear
linear dispersity
Von Bekesy also observed that a given freq stimulus reaches a peak in vibration amplitude at a ______ and characteristic spot along length of the cochlea
constant
for any given freq stimulus, the vibration grows _______ as it moves along the length of the cochlea then more abruptly ___________ after achieving its max vibration
gradually; diminishes
as the frequency of the stimulus is _________, the position of the vibration max moves towards the base of the cochlea
increased
Von Bekesy’s Assumptions (3)
1) Reissner’s membrane acts similarly to BM
- fair assumption
2) Dead cochlea functioned similarly to undisturbed live cochlea
- not a fair assumption
3) To see vibration waves, Von Bekesy had to use stimulus intensities that were on the order of 130 dB SPL (above pain threshold)
- not a fair assumption
Von Bekesy’s shortcoming
did not account for the sharp tuning of the individual auditory fibers
Sellick used other techniques such as
Live animals
Sellick clarified important points such as (3)
1) BM was responsive to low level stimulus
2) BM was very sharply tuned at this intensity; changing the stimulus freq only slightly caused a LARGE change in vibration amplitude
3) BM response became more broadly tuned as stimulus intensity increased
Sellick’s model/diagram
the vibration energy of the stapes is tightly coupled to ________
basilar membrane (BM)
Helicotrema acts mechanically as if it were ___________ except at very low frequencies (<100 Hz)
closed
What does the helicotrema help do?
filter out very low freq sounds such as body sounds of breathing and heart beat
the __________ ear is most efficient, but vibration of the skull (tuning fork) works well also
middle
the primary determinant of frequency-to-place transformation is the
gradient of stiffness along the BM
the BM represents a _____________ system
non linear
what does a non-linear system represent
increases in sound intensity does not result in corresponding increases in vibration amplitude of the BM
____________ and ____________ are the results of active physiological process and for this reason, are vulnerable to the disease of that physiology
tuning and non-linearity
Von Bekesy’s studies could not explain the _________________
high frequency resolving power that the live cochlear must exhibit
