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Re: mechanical cochlear model
Richard F. Lyon wrote Tuesday, March 16, 2010 4:10 PM:
...... This is surely an original view, which
would be totally new to the community of Bekesy's followers, who
have always maintained that a displacement of fluid volume via the
cochlear windows was a precondition of a basilar membrane traveling
Martin, if anyone has maintained such a thing as a precondition, in
such a strong form, it would be good have a reference to it.
No problem. In their often referenced review "Mechanics of the Mammalian
Cochlea" Robles and Ruggero (2001) write as follows:
"Pressure waves reaching the eardrum are transmitted via vibrations of the
middle ear ossicles to the oval window at the base of the cochlea, where
they create pressure differences between scala tympani and the other
scalae, thus displacing the BM in a transverse direction."
I can agree with Robles and Ruggero here, but they are not supporting your
concept "that a displacement of fluid volume via the cochlear windows was
a precondition of a basilar membrane traveling wave." They are not ruling
out rocking motion creating a pressure difference across the membrane via
a traveling wave.
It is not "my concept", but that of Bekesy, here adopted by Robles and
Ruggero. When these authors write "pressure differences between scala
tympani and the other scalae" they say that in scala tympani there must be a
pressure that is different from that in the other scalae. This means that
stapes motion must change the pressure in scala tympani. A piston-like
motion of the stapes, with a sufficient amplitude, does this. A rocking-like
motion does not do it. A rocking-like motion, however, causes a sound wave
("compression wave") in scala tympani, without changing the pressure in this
Again, Bekesy, Robles and Ruggero, and some others, consider a pressure
change in scala tympani as a precondition of a hair cell response. The data
of Huber et al. (2008), as quoted earlier in this thread, and several other
sets of data have disproved this view. Hair cells do respond without a
pressure change in scala tympani.
Just some examples of the other data sets:
..,,,,,. The notion of "sufficient energy" is peculiar in this
context, as if below some threshold something would not move.
Not "peculiar", but self-evident. Everything that is moved by external
forces has a threshold. Below this threshold it is not moved. The thinnest
branches of a tree may have a threshold of 0.5 m/s wind speed, whereas the
thickest branches of the same tree may have a threshold of 20 m/s wind
speed. You are not trying to tell us that everything that moves in the
cochlea has got the same sound-level threshold, are you?
This "threshold" concept is to me "peculiar", as a person trained in
linear systems. Do you have some sources for it where I can try to
The "threshold concept" is a central one in most empirical auditory
research. In particular, in recent years the differential motion of
mechanical elements within the cochlea has been in the focus of empirical
research of the inner ear. For example, the lab of Alfred Nuttall reported
that at the same characteristic frequency (CF) place the basilar membrane
and the reticular lamina moved independendly from each other.
F. Chen, J. Zheng, N. Choudhury, S. Jaques, A.L. Nuttall (2009) Organ of
Corti micromechanics with local electrical stimulation. In: NP Cooper, DT
Kemp (eds) Concepts and Challenges in the Biophysics of Hearing. World
Scientific Publishing, Singapore, pp. 135-140.
There is a gain in energy from the entrance of the cochlea to the hair
cells. That's what the cochlear amplifier is about.
The gain takes place within the outer hair cells (OHCs), which are the
motors of the cochlear amplifier. The amplification of a by-passing basilar
membrane traveling wave by OHCs is physically impossible, because the motor
activity of these cells has a latency. Even a delayed secondary traveling
wave produced by OHC activity has never been observed. The data from the
labs of Russell and Ren show no basilar membrane motion between the stapes
and the characteristic frequency (CF) hair cell excitation area.
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