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Re: mechanical cochlear model
At 12:41 PM +0100 3/16/10, Martin Braun wrote:
Richard F. Lyon wrote on Monday, March 15, 2010 11:27 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
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.
..,,,,,. 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
Energy is not the issue. Pressure is needed; ........
There is no pressure without energy, and the energy question has
always been a central one during the history of cochlear mechanics.
You took my "energy is not the issue" away from its context...
There is a loss of sound energy at the entrance to the cochlea, and
there is one on the way from this entrance to the detecting hair
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 energy loss at the entrance is greater in case of a fluid displacement.
The energy loss on the way to the hair cells is greater for a
membrane traveling wave than for a sound wave ("compression wave").
These things are pretty evident, and they are dictated by the laws
of energy absorption due to friction.
In conclusion, an "engineer" building a sensitive ear that is
depending on membrane traveling waves would make a big blunder.
I remain baffled.