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Could a cell membrane provide an electromagnetic shield ?

r norman rsn_ at _comcast.net
Tue Feb 10 22:15:26 EST 2004

On 11 Feb 2004 02:04:08 -0000, stelmed at freemail.gr (Stelios
Papaioanou) wrote:

>Hello everybody!
>I would like to ask you the following question:
>If we apply an external electric field of 10 v/m very close
>(~micrometers) to the surface of a neural cell membrane, what would be
>the value of the electric field that is measured inside the cell.
>Consider the cell membrane's resistance ~5 ohm/m2. Cell membrane has
>also capasitance characteristics (Don't know the exact value).

I don't really understand just what you are proposing.  If the field
strength is 10 v/m, it doesn't matter how close it is.  Considering a
cell might be 10 to 100 um in size, there would be a voltage of less
than 1 mv across it.  This is a very small value.

Note that the cell membrane of somewhat under 10 nm thickness supports
a membrane potential of somewhat less than 100 mv.  That amounts to an
electric field in the membrane of 10 million volts/meter!

The salt solutions inside and outside the cell have fairly low
resistivities and act as pretty good eliminators of electric fields
within the solutions.  Incidentally, the membrane capacitance is
pretty close to 1 microfarad/square centimeter or 0.01 farad/m2.

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