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Re: mechanical cochlear model
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
wave.
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."
http://physrev.physiology.org/cgi/content/full/81/3/1305
..,,,,,. 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?
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. 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 cells.
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.
Martin
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Martin Braun
Neuroscience of Music
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Sweden
email: nombraun@xxxxxxxxx
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