Subject: Re: mechanical cochlear model From: "Richard F. Lyon" <DickLyon@xxxxxxxx> Date: Tue, 16 Mar 2010 08:10:20 -0700 List-Archive:<http://lists.mcgill.ca/scripts/wa.exe?LIST=AUDITORY>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 >>>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 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 understand it? >>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 >cells. 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. Dick