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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." 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.

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 scala.

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 understand it?

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.


Martin Braun
Neuroscience of Music
S-671 95 Klässbol
email: nombraun@xxxxxxxxx
web site: http://www.neuroscience-of-music.se/index.htm