An electrophysiology quesiton
k p Collins
kpaulc at [----------]earthlink.net
Tue Feb 10 16:30:52 EST 2004
I comment with respect to "capacitance",
"Christian Wilms" <usenet at out-of-phase.de> wrote in message
news:1g8xwye.12xgfy85v29dsN%usenet at out-of-phase.de...
> Xiaoshen Li <xli6 at gmu.edu> wrote:
> > I am always confused EPSC and EPSP.
> > In voltage clamp condition, are we
> > measuring EPSCs?
> Yes, under voltage clamp you measure you
> are measuring EPSCs. It tends to be confusing
> at first, but after a while one gets acustomed to it.
> When you voltage clamp a cell that means you
> are injecting a current in order to keep the cell
> at a constant voltage. What you measure is that
> injected current.
> When you current clamp a cell you are injecting
> a constant current into that cell and what you
> measure is the resulting voltage of the cell (the
> cell potential). The name current clamp is a bit
> misleading, as it implies that you are keeping
> the current through the cell membrane constant,
> which you are not.
> The connection between postsynaptic currents
> (PSC) and postsynaptic potentials (PSP) isn't
> as trivial as it might seem at first. Ohm's law
> is only one of the factors, that play a role here.
> More important is that the membrane functions
> as a capacitance _and_ a resistor. Because
> of this capacitance PSP are always longer than
> the PSC which causes them.
> Hoping that I did add too much to your confusion, Chris
"Capacitance" is =just= the current that is allowed
by "resistance", so Ohm's Law is, in fact, all that's
It's 'just' that "resistance" is dynamic.
This isn't a 'trivial' matter.
Nervous systems do their version of setting an
analog computer's "zero-points" by, literally,
dynamically setting "resistance".
For those who have AoK, this is what "biological
mass" [Ap5] is, and why "biological mass" embodies
Tuning "resistance", determines conductance, which
There's no 'magic' in any of this.
See my earlier post, here in b.n, with respect to
the "Binding Problem".
Protein synthesis establishes "biological mass", and
this "biological mass" is dynamically-tuned ['addressed']
in accord with the activation that comes from the
environment. This tuning includes dynamic 3-D
conformational and conductance variations that occur
within neural glia.
The conformations of proteins are activated by the
=net= ionic conductances.
But, modify "resistance", and, of course, "capacitance"
is modified in a rigorously-coupled way.
Cheers, Chris, ken [K. P. Collins]
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