An electrophysiology quesiton
k p Collins
kpaulc at [----------]earthlink.net
Tue Feb 10 14:41:29 EST 2004
Hi Xiaoshen, despite the way all the
'intelligent' folks are 'beating-me-up',
I gave you all that's necessary, yester-
Although I Expect you already-Know,
I'll explain, further, below.
"Xiaoshen Li" <xli6 at gmu.edu> wrote in message
news:c0arfk$iul at portal.gmu.edu...
> Dear Everybody:
> Thank you so much for your help. I
> greatly appreciate it.
> Please correct me if I am wrong:
> (1)In voltage clamp mode, we usually
> clamp the neuron's membrane potential
> at its resting membrane potential (say
> -65mv) by using some electric engineering
> amplifier device. When presynapse fires,
> the postsynaptic channels open, in an
> excitatory case, the current will flow
> into the neuron (EPSC) which intends to
> depolorize the neuron membrane. So the
> V-clamp circuit will draw the current
> outward to mantain the neuron Vmem
> unchanged. The drawing out current in the
> amplifier is what is measured. It is equal
> to the current flowing at the synapse(EPSC).
> What is called "EPSC" is actually the
> amplifer reading.(2)In current clamp mode,
> I am very unclear now. I guess, we clamp
> the neuron at a constant current through
> an amplifier too. (How much current should
> an electrophysiologist choose usually?) Say
> we choose to inject a small constant
> current(Io) into the neuron. So, neuron
> membrane potential will rise from its
> resting potential in the beginning with
> certain time constant. After a period,
> Vmem reaches a plateau, steady state
There is no such thing as a "steady state",
and it's =IMPORTANT= to get, and
keep, this straight.
Yeah, one can adjust the energydynamics
so that the meter-reading points to a spec-
But the meter's pointing to a specific mag-
nitude =always= derives in an energy-flow,
and =any= energy-flow constitutes a non-
Calling such a "steady state" is like driving
one's car at super-highway speeds, and
saying that one is not being transported at
Yes, one can adjust the pressure one ap-
plies to the accelerator pedal so that one's
car's speedometer points to a specific mag-
nitude, but it does no good to call either the
pressure one applies to the accelerator pedal,
or the speedometer reading, a "steady state" -
because doing so 'blinds' one to the energy-
dynamics that are what's actually occurring.
Why focus upon that which, in doing so,
renders one 'blind' to =everything= that's
Remember, the Problem that we are addres-
sing is "how nervous systems work", not "how
can we get the meter to point to a specific mag-
The former Problem is everything, and the lat-
ter 'problem' is =nothing.
Going back to the automobile analogy, yeah,
one can avoid getting a speeding ticket if one
attends to accelerator-pedal pressure, or
speedometer reading, but that's not the Problem
we are discussing.
We don't care how many 'speeding tickets' we
get. We want to understand the energydynamics,
and how they enable all of our car's functionalities.
And, if we want to do so completely, we must,
simultaneously, understand the energydynamics
through which our nervous systems selectively
[by-]produce accelerator-pedal pressures,
al transitions, etc., all so that we not only stay on
the road, but optimize our 'getting-where-we-want-
Focus on anything other than the energy-flow, and
how and why it's vectored, and one sees =nothing=
that matters - except not getting a 'speeding-ticket'.
There's no such thing as a 'steady state'.
Understanding this one thing is absolutely-essential
in understanding the Problem that we are discussing.
The meter-reading has worth =only= when we
use it to see the non-steady-'state' energydynamics.
> (Vmem=Io*Rmem). Since Io is small, Vmem
> will not be high, so no action potential firing.
> When presynapse fires, postsynaptic channels
> open. In an excitotary synapse case, the driving
> force will push current flow into the neuron
> through the opened channels. This current
> cancels part of Io. To keep the current constant,
> the amplifier device will increase its voltage
> potential to inject more current. The extra
> amount of current is equal to the current flowing
> in at the synapse. This amplifier volatage
> increase is measured and is called EPSP.
> If I am correct most part above, what are the
> advantages/disvantages of EPSC and EPSP?
There is no advantage either way, which is what
I was discussing in my prior reply. One can work
with =any= data that allows one to 'see' the under-
pinning energydynamics - one can use "voltage",
one can use "current", one can use "firing-rate",
one can use tagged-ion-movement, one can use
external observables, like effector activations and
limb-movements, etc. There are =Infinite= ways
of doing the 'same' thing, and this Infinity Exists be-
cause of the stuff that I discussed in my prior post.
Where ever one looks, one sees stuff that's 'one
side of the same coin', and everything else can,
in principle, be calculated from it - be-cause of
the stuff I discussed in my last post - the "Wheat-
stone Bridge", "Ohm's Law", "analog computers".
And it's =Vital= to get this one thing straight, and
keep it straight - be-cause =IT IS THE UNDER-
PINNING 3-D ENERGYDYNAMICS= that
constitute the Information that directs the con-
struction of the modifications to the neural arch-
itecture through which the nervous-system-'analog-
computer' dynamically varies 'resistances' so that
the 'zero-points' of the 'analog-computer' come to
be, with specific correlation to the problem with
respect to which the nervous system is Calculating,
So, if one 'throws-out' the underpinning energy-
dynamics, so that one can attend to the meter's
reading, one 'throws-out' =everything= that one
actually needs to understand.
The underpinning 3-D energydynamics are
> How is an electrophysiologist going to choose
> to measure EPSC or EPSP in his today's
As above, "voltage" or "current", it doesn't matter
because they're both just 'opposite sides of the
same coin', and everything can be calculated us-
ing either [=of course=, only when such is done
in a way that is, itself, relevant with respect to the
overall 3-D energydynamics. [One can't look at
one gate and say what the rest of the nervous
system is doing :-]
> (3)In real life situation(no V-clamp, no I-clamp),
> a neuron sits there with Vrest=-65mv.
It's a Certainty that the neuron is =not= just sit-
ting there. It's a Certainty that the neuron's being
acted-upon so that the =meter-reading= points to
a specific magnitude is actually =driving= the
neuron's protein-synthesis in a way that's uniquely-
correlated to the 3-D energydynamics that are
being imposed upon the neuron.
This has to be kept-straight, or one will 'avoid
getting speeding tickets', but one will never 'get-
anywhere' with respect to understanding the
neuron's information-processing dynamics, nor
nervous system function.
> When an excitotary synapse fires and the
> postsynaptic channels open, due to the driving
> force difference, the current will flow into the
Why is what I discussed in the Googled post
that I referred to in my prior reply.
> This current will charge the neuron membrane
> and depolarize it. Is this current equal to EPSC
> measured? Is this membrane potential change
> equal to EPSP measured?
Here, I'll leave the 'symantics' to the others who
obviously love 'avoiding speeding tickets' - er,
But I've explained the 3-D energydynamics.
To all, in the discussion, above, with respect to
the way the nervous-system-analog-computer
calculates 'resistences' so that the 'zeroes' will
be set 'appropriately', I've Disclosed the final
piece of the 'puzzle'.
I Declare the nervous system Solved to a
level that's commensurate with Special and
Thank =YOU= very much for your help.
ken [K. P. Collins]
> Thank you very much for your help.
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