Reversal potential/Equilibrium potential Definitions! (should be easy for you guys)

KP-PC k.p.collins at worldnet.att.net%remove%
Wed Apr 30 13:50:08 EST 2003


Hi Richard. Thank you for your generously Thoughtful discussion.

More below.

"r norman" <rsnorman_ at _comcast.net> wrote in message
news:nnjvavgcbf7su3h2he78rm3ev8jrl90b35 at 4ax.com...
| On Wed, 30 Apr 2003 00:25:12 GMT, "KP-PC"
| <k.p.collins at worldnet.att.net%remove%> wrote:
|
| >Hi, Richard.
| >
| >"r norman" <rsnorman_ at _comcast.net> wrote in message
| >news:5nrsavgildi2i904qud2hmed640iv08sbm at 4ax.com...
| >| On 28 Apr 2003 08:43:05 -0700, chrismin at bigpond.com (chrissy)
| >wrote:
| >|
| >| >Just a simple question (hopefully):
| >| >What's the difference between the reversal
| >| >potential and the equilibrium potential for ion
| >| >flow in neurons?Both have to do with balancing
| >| >electrical potentials, don't they?
| >|
| >| This is always a subtle distinction for students.
| >|
| >| If a channel is permeant to a single ion, then
| >| the reversal potential is, in fact, the equilibrium
| >| potential for that ion.  At membrane potentials
| >| more negative, the ionic currents flow one way
| >| and at membrane potentials more positive,
| >| they flow the other way.  At thespecific value,
| >| the currents reverse (reversal potential) and the
| >| diffusion and electrical forces cancel (no net
| >| change in delta G, theequilibrium potential).
| >|
| >| The real distinction occurs with the numerous
| >| synapses where a channel allows several types
| >| of ion through. For example, the vertebrate
| >| neuromuscular junction nicotinic receptor/channel
| >| allows both Na+ and K+ through.  So the reversal
| >| potential is neither EK, the potassium equilibrium
| >| potential nor KNa, the sodium equilibrium potential,
| >| but some value approximately halfway between
| >| these two.  At thereversal
| >| potential, neither ion is in equilibrium.  Still, the
| >| influx of Na just balances the efflux of K so the
| >| current is zero.
| >
| >But the "zero" isn't actually the same thing twice.
| >
| >Please come back, if I didn't establish this 'point'
| >in my reply to"New Zelander".
| >
| >Your 'point' in your 2nd paragraph is some of it -
| >it's not only "some value approximately halfway
| >between these two", that 'combinatory'-value is,
| >itself, never the same [regardless of what
| >the meter says :-]
| >
| >[I'm taking advantage of folks' focus to [hopefully]
| >lift folks' understanding up to the 'level' of integrated
| >nervous systemfunction.]
| >
| >ken
|
| Ken, I think your questioning the nature of "zero"
| is really about the following point.
|
| The real distinction between equilibrium potential
| and reversalpotential is the true subtlety that students
| fail to appreciate. That is: the reversal potential is an
| empirically determined value that you discover by
| performing an experiment.  Clamp the membrane
| potential, systematically varying the value. Measure
| the synaptic current.  Plot current vs. potential.  You
| get a plot that crosses the x-axis (zero current) at
| some potential.  That is the reversal potential.  To the
| left (more negative potentials) the current is outward.
| To the right (more positive potentials) the current is
| inward.  There is no problem with defining "zero" or
| interpreting what it means.  Zero means no
| (additional) current flows through your clamp
| equipment caused by the opening of synaptic channels.
| What is actually happening at the synapse is a matter
| of interpretation. You are right in that this zero
| is really the cancellation of two ongoing processes,
| both subject to fluctuation from other circumstances
| (that may alter ionic concentrations, for example).
| That is, it is not an "absolute" or fixed point.
|
| The equilibrium potential is another story completely.
| It is a theoretical value based on physical chemistry
| and the Nernst equilibrium.  It is not at all something
| that you measure.  However, according to the ionic
| theory of membrane behavior (i.e., the membrane
| contains channels that allow ions to move solely
| according to the laws of diffusion and electricity)
| then under certain very special conditions, you
| should expect an actual measured potential to be
| equal to that conceptual or theoretical value. The
| special conditions are that the membrane be
| permeable to only one ion (or if it permeable to
| more than one, that they all obey the Donnan condition
| so they can all be in equilibrium at the same time).
|
| The fact that the reversal potential for a particular
| synapse matches the equilibrium potential for a
| particular ion is the experimental evidence that the
| synaptic channel is specific for that ion.  A more
| throrough experimental test would be to vary the
| equilibrium potential by changing the ionic
| concentration and verifying that the reversal
| potential changed in exactly the same way.
|
| Ken, you have a second extremely valid point that
| you consistently emphasize -- that the nervous system
| is a very complex, integrated, holistic entity.  Everything
| influences everything else and a purely molecular,
| physical chemical approach does not lead to a real
| understanding of what is happening.  Again, that is
| very true.
|
| However, you also have your own theories about how
| to deal with the situation, and that is another story, entirely.

Please Forgive me, Richard. In my reply, as usual, I'm once again
'long-winded' as I seek to 'paint the picture' in various
complimentary ways [I've reread it's 'off-the-top-of-my-head-ness'
[for a change], and also see that it could use some reorganization,
but I'll leave it as it is.].

I did deliberately 'harden' my discussion [did do it in a TD
E/I(up)-inducing way] - to imbue it with some 'stickiness'.

I do not 'discount' empirical results.

I've only taken a stand against the way that 'dangling'
[non-integrated] empiricism 'blinds' folks to what's actually going
on in-there.

Yes, an ion channel is like a functional-'unit'. It can be studied
'as a unit' in 'isolation'.

But doing so introduces artificiality, and such has to be
kept-straight.

In vivo, the channel is not isolated, and its functionality [whether
it will 'gate', in which direction it will gate, whether it'll 'hold'
its 'state', and even whether it will have continued existence, be
joined by other newly-synthesized channels that're synthesized via
the ongoing 3-D energydynamics, and the resultant 'balance' amongst
channels' functioning, it's location within the 3-D neural
architecture, etc., all impact and reflect the =overall= energy-flow
that the channel experiences, and all vary as a function of the 3-D
energydynamics that actually occur within nervous systems.

My 'problem' is not with respect to anything empirical, but with
respect to the way that what's empirical is, in my [considerable]
reading experience, always presented, discussed, etc. in the absence
of the 'larger' ramifications that I've been discussing in this
thread.

The 'difficulty' derives in relative 'unfamiliarity' that gets its
start in college and grad school and, in a hand-me-down way, gives
'short-shrift' to what actually occurs in nervous systems. From
there, groupwise TD E/I-minimization 'just' perpetuates the
short-shrifting.

It's why, in one of my posts in this thread, I quoted the famous line
from _The Network_ "I'm mad as hell, and I'm not going to take this
anymore!" [I regret not having included a 'smiley' - 'cause my
purpose was Loving with respect to our Science. But I was literally
saying that the "short-shrifting is at an End". I'm going to do
what's necessary to Stop-It - to lift Neuroscience up above it.

I understand that it seems that I'm making "much ado about nothing",
but look at the current question in terms of the global TD
E/I-minimization dynamics that're discussed in AoK.

If there were =anything= 'absolute' within the globally-integrated
functional energydynamics of nervous systems, to the degree of such,
Convergence would be flat-out Impossible - the 'absolute' thing would
'dictate' to the rest of the system - it's 'absoluteness' would be
'the goal' that's a priori 'determined' regardless of whatever else
happens within nervous systems.

If that were the case, then, why 'bother' even having a nervous
system?

All that could be 'converged' upon within a nervous stytem that
incorporated such 'absolute' stuff would be a priori 'determined' by
the 'absolute' stuff.

I suspect that the position I've discussed is not yet communicating
sufficiently.

Let's see, what's a more-useful analogue?

The general thing is that, prior construction 'exists-within' - is
'contained by' - any new construction that's constructed 'on-top-of
it.

You're looking at a channel as 'a brick'.

I'm looking at a channel as a 'brick' in an edifice - undergoing the
3-D 'stresses' that derive in it's contribution to the entire
structure, and the structure's overall engineering dynamics.
[Be-cause of WDB2T, there exists no such thing as 'Statics' within
physical reality.]

I understand that it's 'difficult'. I'm getting into Tapered
Harmony's stuff [a theory in Physics, that's not [yet] accepted by
Physicists, so it's 'difficult'.

But I stand on what I've posted.

A meter can read "zero" but it's "zero" is actually never the same
thing twice, and it's important to understand this.

I'm just saying that it's good to understand the limitations of
'meters', and see beyond their readings into what's actually going on
in-there.

My 'heart' is 'Heavy', Richard. There's no 'easy' way to state my
position.

Please Forgive what I understand must seems to be 'obstinate
ignorance'.

It's not.

It's just that my position induces TD E/I(up) because it's not yet in
the books, not yet taught in grad school, and, therefore, relatively
'unfamiliar'.

What I'm doing is working to lift folks up in understanding.

'Heavy-lifting."

Giving the stuff from which "biological mass" [AoK, Ap5] can be
constructed via subsequent TD E/I-minimization - constructing the
stuff out of which understanding will grow during the courses of TD
E/I-minimization within folks' nervous systems.

See the 'brick' in the edifice, not the 'brick' in the Mason-Tender's
hand. Not the raw materials from which the 'brick' is manufactured.
Not the energydynamics through which it is fired.

See the 'brick' 'containing' the 'memory' of all of this other stuff,
as it exists within the edifice - experiencing the 'stresses' and
'strains' inherent in the overall energydynamics 'memory' of the
edifice.

The 'brick' can be counted.

The meter can be read.

But, it cannot be separated from the overall energydynamics.

Within them, the 'brick' is =not= the same 'brick' that it was when
it was in the Mason-Tender's hand.

So, since nervous systems are always undergoing activation-dependent
change, the meter's "zero" is never the same thing twice.

All of the 'stresses' and 'strains' of the global 3-D energydynamics
that are imposed upon it during the course of activation-dependent
trophic dynamics are literally in-it as nervous systems experience
further activation.

This 'variance'-in-its-"zero" is the channel's contribution to
Learning.

It's the difference between, say, a TV set, or a computer -
mechanisms that do some fancy stuff, but which cannot Learn - which,
given this or that, will always do that or this because their
components are engineered to function in relatively-absolute ways,
and nervous systems.

Within TVs' and computers' components, their manufacturing
tolerances, their "zeroes" are 'always' "zero".

Nervous systems differ from this.

It's 'funny'. As I'm writing this, I'm smiling because, of course, if
a channel is isolated, none of this can be seen. The procedural
isolation 'eliminates' everything that's in my discussion -
eliminates the possibility of seeing it.

The position I've taken can be Tested via experiment, however.

Doing this would require the cross-correlation of scan data with
electrode data - a merging-synthesis of all data pertaining to in
vivo 3-D energydynamics.

It's a Hard experiment, but it can be done.

It will disclose the variation of the meter's "zero".

I see the variation in my 'meter's "zero", plain as day, in the way
that, when I 'push energy', I See farther than I could before I
'pushed the energy' that I 'pushed' :-]

The 'standard' position(?) is that, within such, a channel's
"reversal potential" is always the same(?) - that it's just an
absolute 'cog' in the 'gears' of a neuron's innate dynamics(?).

OK, OK - it's always "zero volts" :-]

But, then, if learning is to occur, what a "volt" is must vary :-]

My position differs from the 'standard' one, although, yes, their's
always the ionic-conductance directionality 'reversal', - always the
'axis-crossing' - the 'coordinate system' upon which the "zero" is
read is, itself, continuously undergoing 'translation' [Maths:
"coordinate-system translation"] that's rigorously-coupled to the
overall 3-D energydynamics.

So, the meter's "zero" is never the same thing twice.

It varies as a function of the 3-D trophic dynamics [the construction
of "biological mass", having physically-real information-processing
inertia] that constitute 'Learning'.

It's why, through the doing of information-processing work, one can,
'now', do more than one could at some 'time' in the past - and why,
the more information-processing work that one does, the more
information-processing work that one can do, and the easier doing
such information-processing work becomes.

Everything in-there is as a single 'stressed' structure within which
everything varies in rigorous accord with the 'stress that it
experiences within the overall 3-D energydynamics.

It only seems like "much ado about nothing" because it's relatively
'unfamiliar'.

In Truth, it's Fundamental to nervous system functionality. [It's as
'difficult' as General Relativity, BTW, [literally going beyond GR
with respect to Universal energydynamics], so folks should not
question 'self'. It's just 'difficult'.]

Good gosh! My 'heart' is so 'heavy', Richard - to know that I have to
persist in 'disagreeing' [when I'd much rather just 'go with the
flow', in order to gain 'membership'] - but I Hope there will be Joy
in the end - after the 'difficulties' are worked-through.

The meter's "zero" is never the same thing twice.

If I'm just being 'obstinate', then someone, please, show me the
'boundary-line' between that which is 3-D dynamic, and that which is
'static'.

I'll need to see, and comprehend, such before I can see anything
other than what's in the position I've taken in this thread.

I don't expect, though, that anyone will be able to show me such a
'boundary-line'.

It makes a difference. What I've actually been doing in this thread
is, as usual, working to 'chip away' at the prevailing absence of
understanding with respect to =global= nervous system function.

"Whittling" [AoK, Ap5] on the raw materials at hand.

[I 'dread' posting this - 'dread' being, yet again, 'the bad guy' for
having only done what needed to be done.]

"Oh well."

Cheers, Richard, ken [K. P. Collins]

--
"Schmitd! Schmitd! Ve vill build a Shapel!"






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