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Re: mechanical cochlear model

Peter van Hengel wrote:

I don't think there is a question whether or not there is a traveling wave
in the cochlea. Fluid mechanics dictates that there has to be one.

There has to be one, if a volume shift of cochlear fluids occurs. Such a volume shift apparently occurs at high sound levels (>60 dB SPL). However, to induce sound waves in the cochlear fluids and also a hair cell response there is no need at all for a volume shift. This was recently demonstrated by Huber et al. (2008) in a series of elegant experiments:


In other words, sound waves can enter the cochlea and excite hair cells without a fluid displacement and without causing a traveling wave.

The problem I see with a compression wave being the stimulus and the
haircells acting as pressure sensors .....

Hair cells need not be pressure sensors for a response to sound waves (compression waves). The "hairs" of the hair cells can act as wave detectors. Already today we see that they apparently do this in lizard ears. Manley (2006) measured spontaneous otoacoustic emissions (SOAEs) from ten lizard species that have no tectorial membranes. In these animals free-standing hair bundles vibrate through their own motor mechanism and thereby produce sound waves in the inner ear fluids that are measurable from the outside. There is no reason why this process should not work in reverse as well, such that hair bundles respond to sound waves that have entered the inner ear fluids from the outside.

Manley GA (2006) Spontaneous otoacoustic emissions from free-standing stereovillar bundles of ten species of lizard with small papillae. Hear Res 212, 33-47. http://www.ncbi.nlm.nih.gov/pubmed/16307854


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