Axon: Soliton? Analogies and Divergencies

[bernard]

Another difference

[bernard]

And another one;

[bernard]

Originally Posted by BB

The ion transfer is an active as well as a passive process which creates the ionic current. How is that transformed into the wave like propagation you demonstrate?

Here is simple visual explanation:



You may consider membranes patches as little tanks that contain definite # ions. Each machine is linked to the following by a valve (ions channels) controlled by the level in the bottom tank.
When ions enter the lower chamber, it changes the internal conditions of the next voltage sensor pad and then this one, will let enter the content of the top tank.

This point of view respects the notion of capacitance.
An it introduces a notion of delay.

[bernard]

Of course the previous post doesn't explain the initiation of the action potential since we need that some positive ions enter in a bottom tank, starting the chain reaction.

Really? But there is a simple way to walk around this problem!!!

[bernard]

Some of you may have found the model explains, also, refractory periods, in an elegant manner that is explained here.

But I need to explain the threshold level.

[bernard]

You need a membrane patch where it is figured some blue areas: These zones are the limits (at 1/10) of influence of the center of the ion channel (the center of attraction for our electrostatic forces).
You have to remember that Nature needs a system that works in quite all circumstances. Thus, it needs a good "noise immunization" then its sensitivity is limited by design.

[bernard]

I forgot to say that you could consider some initial conditions;
The stimulation is weak or may be large.
An electric stimulation implies a ion motion: ions are attracted or repulsed by the electric field.

It is this ion motion that opens the ions channels.

[Diane]

Is this neurophilosophy blog post of any congruence with/use to/support for what you are elucidating, Bernard?

[bernard]

Yes, for some pieces and no for the most of this blog.

[bernard]

Back to the stimulation simulation.
It seems obvious to suppose there is a direct link between the stimulation current and the stimulated area.

Then, it becomes also obvious that you need a minimal amount of stimulation to provoke an action potential initiation. It works only if you can move a definite number of ions channels at the same time.

[bernard]

The traditional theory about action potential is described here =>
http://nerve.bsd.uchicago.edu/med98d.htm#Propagation

There is a figure that shows the process:
Diane will remind herself the passive spread current (electrotonic current).

The analysis of the voltage distribution along the axon as a function of time for a stimulating current step in the center is shown schematically in Fig 33. In this case, the axon is immersed in a large bath of solution, therefore we may consider the external resistance close to zero, which makes the outside essentially isopotential. For this reason, the diagram is showing only the internal resistances connecting the membrane patches. Fig. 33 shows the current intensity as darkness in the wires, and it also shows the voltage distribution as a function of distance after we have waited a long time and all the capacitors have been charged to their final value (for this reason the currents are only in the resistive branches). When the pulse is suddenly applied, the current will go mainly to charge the membrane capacitance but most of this current will be taken by the capacitance closest to the electrode and much less by the capacitance further away because the internal resistance produces a voltage drop (V=ir) and less voltage will be seen by the distant capacitors. This initial capacitive charging may be considered like a short circuit at short times. As the capacitance near the electrode gets charged, the current in that region decreases and more can go to regions farther away and charge the rest of the axon capacitance. This means that regions far away from the current electrode will start increasing their voltage with a time lag.

[BB]

OK, I think I'm catching up. You are showing the difference between electric conductance (the term most commonly used when describing neural function) and propagation (more accurate).

I understand the tank model you made. I remember myelin creates space between the tanks but creates a mode in which the tanks still communicate with eachother or propagate eachother as if they were still directly next to one another, allowing for speedy propagation over long distances.

Could you tie these two things together for me bernard? I remember you making the point that myelin was not like a conductor but instead like a sheath around a hose helping a wave to propagate quicker. I took this literally to mean you thought there was an actual physical wave within the neuron. Now I think you were using that example to demonstrate this difference between conductance and propagation. Am I with you?

Also, I remember Kandel writing of gap junctions as actually having some electric properties different than the propagation properties of a synapse. I'll try to find it tonight.

Thanks!

[bernard]

Cory,

You begin to understand the thing but some notions remains fuzzy in your mind. That comes from my language problem.
Gap junctions are another affair and myelin wasn't "reached" at this time of discussion.

[bernard]

Originally Posted by BB

OK, I think I'm catching up. You are showing the difference between electric conductance (the term most commonly used when describing neural function) and propagation (more accurate).

I'm speaking about propagation telling differences that exist between a real electric circuit an the one described arbitrary in axons.
The second uses components that have properties that are far from those described and known.

Originally Posted by BB

I understand the tank model you made.

The upper tank is the external side of the axon like here
The lower tank is the opposite side of the membrane under the ion channel.
The tube is an ion channel (with a ionic/electric tap).

Originally Posted by BB

Also, I remember Kandel writing of gap junctions as actually having some electric properties different than the propagation properties of a synapse.

chemical synapes are the best way to enable communication between neurons of different kinds and it is a way to change their bahaviour.
Gap junctions create networks of synchronous neurons => Super neurons.

[bernard]

Here is a little drawing showing some basic electric rules.

[bernard]

And here is the full diagram of action potential propagation.
I just rounded some clues.

http://nerve.bsd.uchicago.edu/med98d.htm#Propagation

[bernard]

There is some impossible current circulations.
This is strictly forbidden by Physics.

But if this theory violates a single law of Physics then the whole process is then stopped. No propagation at all in these conditions.

I'm working on a large project that obeys to Physics.
Each movie is a bit... long to produce.

Here is the first of 4 (not terminated => 1 or more weeks).

[bernard]

Here is a new picture that shows some examples of electric current circulations that follow normal rules.

I made a mistake in these examples! Are you able to find it?

[bernard]

Of course, my intentional mistake is at the first element and second row: Current can't flow from - to +.

Many of you may think that I'm a bit (sic) nut.

Here is the respectable example found on Wikipedia

http://en.wikipedia.org/wiki/Action_potential
http://en.wikipedia.org/wiki/Action_...al#Propagation
There is a picture at the right.

http://en.wikipedia.org/wiki/Image:A...model_view.jpg

and that is my comment;
http://en.wikipedia.org/wiki/Talk:Ac...gation_Picture

[bernard]

Here is a new movie that shows how it works in non myelinated membranes:

http://www.somasimple.com/flash_anims/ap_seq_02.swf

[bernard]

You may be interested by this section:
http://en.wikipedia.org/wiki/Talk:Ac...g_their_motion

[Diane]

Don't forget that the glia buffer synapses by blotting up excess K⁺.

[bernard]

I asked a difficult question on specialized forums:

On physics forums
Action potential and Na+

On science for everyone
Action potential and Na+

On Science & phisolophy
Action potential and Na+