From: Steven Eiger (eiger@montana.edu)
Date: Sat Nov 17 2001 - 09:30:37 PST
Message-Id: <l03102800b81c4d7c2b3e@[153.90.150.107]> Date: Sat, 17 Nov 2001 10:30:37 -0700 From: Steven Eiger <eiger@montana.edu> Subject: Re: pinhole Nervous system and voltage
>Hi Jhumki
>
Paul gives an explanation that might convince your students, but actually
the voltage is caused by differential leaks of ions across the membranes;
initially more potassium leaves the cell than sodium enters. It is because
there are more channels (conductors) that are specific to potassium than
sodium. This sets up the membrane potential, it is a diffusion potential.
The pumps merel;y maintain the concentration gradients of sodium and
potassium. I will attach a fairly long explanation that I hand out to my
students in a college class. I bleive that understanding this process is
incredibly difficult, but also incredibly satisfying. It shows how, out of
chaotic movement, and somea organization comes electrical signalling and
ultimately a brain. Go0od luck, Steve
>There are ion pumps in the membrane of the nerve cells. These pumps move
>sodium, potassium and calcium ions. Negative ions and electrons are not
>directly pumped but move due to electrical forces from the charge imablance.
>
>The ion pumps are batteries.
>
>They create a charge difference bertween the inside of the nerve cell and
>the outside. This charge difference gives rise to a volatge difference. The
>inside and outside of the cell are conductors, the cell membrane is an
>insulator. So the membrane acts as a capacitor. The conductor inside the
>cell has resistance and so acts as a resistor. However a volatge difference
>across one part of a nerve cell triggers the neighboring parts ion pumps to
>turn on. Chemical energy is turned into electrical energy. This is the
>equivalent of an electronic amplifier.
>
>Paul D
>
>Paul "But it is more complicated than that!" Doherty,
>Senior Staff Scientist, The Exploratorium.
>pauld@exploratorium.edu, www.exo.net/~pauld
>
>
>
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Steven Eiger, Ph.D.
Department of Cell Biology and Neuroscience and the WWAMI Medical Education
Program
PO Box 173148
Montana State University - Bozeman
Bozeman, MT 59717-3148
Voice: (406) 994-5672
E-mail: eiger@montana.edu
FAX: (406) 994-7077
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