Re: HC selectivity ... was Re: Physiological models of cochlea activity - alternatives to the travelling wave (Matt Flax )

Subject: Re: HC selectivity ... was Re: Physiological models of cochlea activity - alternatives to the travelling wave
From:    Matt Flax  <flatmax@xxxxxxxx>
Date:    Mon, 1 Oct 2007 13:25:39 +1000
List-Archive:<http://lists.mcgill.ca/scripts/wa.exe?LIST=AUDITORY>

Hi Reggie, Bob and the group,

In the linear case I agree with you Reggie.

But hair cell physiology is not linear. The closest they get is with the 
Goldman-Hodgkin-Katz [1] equation. The furthest they get is with kinetic 
algorithms [references not listed].

For this reason I would write .. actually BEGIN to write the membrane 
frequency dependence with respect to other signals like this

                              1
wc(t) =  =========================================
           ___          _ 
          |__ \        (_)
             ) |  _ __  _ 
            / /  | '_ \| |
           / /_  | |_) | |   r(t)c(t)
          |____| | .__/|_|
                 | |      
                 |_|      


A nonlinear impedance. The time factor being the important change ... 

I don't believe that it is valid to give hair cell selectivity a first 
order electrical model.... Sorry ... as simple as that...

For this reason, previous assumptions on the frequency selectivity of 
the cochlea hair cell is - in terms of frequency distributed power - 
incorrect.

A lot of mind or mathematical models may have incorrect assumptions to 
date.

The time dependent model should be able to explain frequency dispersion 
and a certain amount of hair cell adaptation.

sincerely
Matt

[1] @xxxxxxxx{Hille:2001,
  title = {Ion Channels of Excitable Membranes (3rd Edition)},
  publisher = {Sinauer Associates},
  year = {2001},
  author = {Hille, B.},
  month = {July},
  url = 
{http://www.amazon.fr/exec/obidos/ASIN/0878933212/citeulike04-21}
}



On Sat, Sep 29, 2007 at 11:23:03AM -0500, Reggie Weece wrote:
> Bob and Matt -
> 
> The difference between your two values for the cut off frequency
> appears to be the 2pi factor.  From
> http://en.wikipedia.org/wiki/RC_circuit,
> wc = 1/(RC)  rad/s
> fc = 1/(2piRC)  Hz
> 
> Thus wc = 25000 rad/s (not 25 kHz, as Matt suggested!)
> Bob's calculation of fc = ~4kHz is correct.
> 
> - Reggie
> 
> > Date:    Fri, 28 Sep 2007 08:24:35 -0400
> > From:    Bob Masta <audio@xxxxxxxx>
> > Subject: Re: HC selectivity ... was Re: Physiological models of cochlea activity - alternatives to the travelling wave
> >
> > On 28 Sep 2007 at 12:55, Matt Flax wrote:
> >
> > <snip>
> >
> > > With respect to a hair cell at rest ... take the following general
> > > values for membrane resistance and capacitance :
> > > R= 40 Meg Ohms  ...  taken from [4] for example
> > > C= 1 pF         ...  taken from [5] for example
> > > The first order cut-off frequency would be about 25 kHz.
> > > fc=25 kHz.
> >
> > How do you obtain this 25 kHz value?  Using
> >    f = 1 / (2 * pi * R * C)
> > I come up with about 4 kHz.
> >
> > Best regards,
> >
> >
> >
> > Bob Masta

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