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Re: Cochlea Amplifier models : a new list
Dear A.J. and others,
In my mind there is such a close correlation between measurements of BM
motion and of auditory nerve fiber responses that it's hard to believe
that BM motion is not involved in cochlear function.
Yes, BM motion is involved in cochlear function. But which one? Here, the
"relation between BM motion and auditory nerve fiber responses" indeed gives
strong clues, which are highly compelling.
1) At low sound levels:
Here the outer hair cells (OHC) respond to sound pressure gradients in the
endolymph, generate motility, and excite the inner hair cells (IHC) via the
given hydromechanical coupling of the subtectorial space. Nowotny and Gummer
(2006) have reported interesting data on this subject:
A side effect of this BM motility are basilar membrane (BM) excursions.
Hence the close correlation between BM tuning and neural tuning "at
near-threshold stimulus levels" (quoting Mario Ruggero from the abstract of
his Science paper):
Rémy Pujol and his colleagues in France state on their outstanding inner ear
"The traveling wave tends now to be considered an epiphenomenon."
where you have to go to "cochlea", then "physics", then last paragraph.
2) At high sound levels:
Here BM tuning is shifted by about half an octave towards the base of the
cochlea, whereas neural tuning remains unchanged. The effect of this shift
is that BM vibrations absorb acoustical energy, before it reaches the OHCs
that are tuned to the same sound frequencies. Thus it is evident that this
mechanisms must contribute to the protection of OHCs from overstimulation.
In summary, at low sound levels BM vibrations are an epiphenomenon of OHC
motility, and at high sound levels they are specifically tuned to absorb
energy for overload protection.
In engineering, tuned membranes for absorption of acoustic energy, called
silators, are applied for noise control of machines:
Neuroscience of Music
S-671 95 Klässbol
web site: http://w1.570.telia.com/~u57011259/index.htm
----- Original Message -----
From: "A.J. Aranyosi" <aja@xxxxxxx>
Sent: Tuesday, October 09, 2007 6:51 PM
Subject: Re: Cochlea Amplifier models : a new list