Neuron, Myelin and a Ionic Gun

[bernard]

Hi All,

Monday, June 26 was the day! I thought that something was wrong about the theories underlying the action potential propagation but I failed to express it with simple images and words.

Today, I had a confirmation with a paper found on PubMed. It is close to "my truth" but it doesn't give any theory, just brilliant clues. I will upload it during the week but it seems preferable to descontruct before these memes about the marvelous nature of the neuron.

It has behaviours that are more subtle than we thought and an "unified" theory opens doors that seem yet obscure and mysterious.

If something sounds not logical, just ask.
I'll begin with facts. But are they ever facts or sometimes illusions?

[bernard]

1/ Types of axons.

The axon is normally the longest "branch" of a neuron and it is its favoured communication mean over long distances.
There is two types of axons: unmyelinated and myelinated.

The unmyelinated are certainly the older ones in evolution time. They are the ancestors of the second kind. They belong to "old" neurons.
The unmyelinated are thinner than the latters.

Axons carry action potentials. Action potential is a "message". Action potential is a travelling message. Nature realized that it was the best economical way to achieve the purpose of messaging.

This travelling wave is normally unidirectional and the message is sent without disturbance. It has a good noise immunity.
We will see that however that actions potentials are subject of transformation (amplitude) when axons are myelinated.

[bernard]

2/ Natures of Action Potential.

Action potential may be recorded with electric means. This evidence let us suppose that action potential (AP) was strictly electrical by nature. In 1952, Hodgkin and Huxley won the Nobel Prize, revealing a ionic nature of action potential.

Unfortunately, ions fluxes are also measurable by electric means. I say, unfortunately, since we risk to lose some hidden properties that belong to ions.
Moreover, this simple mean opens an easy way to records events but masks other strong invisible forces: Ions act like powerfull magnets and are able to move.

One may say that AP is ionic by natural talent. We may say that is not enough.

I will intoduce a novel property about AP propagation: The ghost/shadowed AP. It will be elucidated, later.

[bernard]

3/ Neglected Aspects

I said in the previous post that we already miss an insightful part of the scene if we reduce observations to the electrical view of AP propagation.

There are some very important aspects that are neglected in the same manner. The physical structure where neuron evolves: the body.
Nothing was really searched about the possible influence of gravitation, pressure and movements => dynamics. They are obviously common parts of our daily lives.
Why, none thought about constraints and possible responses that Nature has used to solve these constant acting forces?

[bernard]

4/ Internal vs External

When the researchers began their studies, they found it was useful to "command" neurons at their arbitrary will. It responded to these artificial sollicitations, hopefully. Actually, nobody denies that external stimulation is useless but are we able to construct a model regarded from an internal point of view. "I'm a neuron and I'm stimulated, what can I do?"

[bernard]

5/ Evolution and Discord

Our world is ruled by evolution's laws. In fact, it seems and we find many clues that confirm these rules. Nature engaged Man to think in a directed manner:

• See my simple marvel!
• It works with simple means.
• Add simple things to enhance it and make another marvel.

Applied to neuron, we will have:

• Myelinated neuron are sons of unmyelinated.
• Their ancestors give them inherited properties.
• These properties are simply enhanced.

Man followed this step of thinking and fell in the Nature's trap.

[bernard]

6/ The Guilty Facts

An unmyelinated neuron "gets" a travelling AP. Its speed is slow.

A "covered" one, which is an enhanced one, shows/confirms that speed is enhanced under myelin by a factor of 100/200. That's great.
The node of Ranvier is the old unmyelinated part (a little bit enhanced, however) and the recorded speed at this site remains slow.

[bernard]

7/ Transient? Ignored!

The major problem encountered by scientists is transient phenomenons. Their duration is ever short and they cost often a lot of energy and induces complex computations.

The myelinated axon has had the same unfortunate story:

• The node has a low speed.
• Under myelin, the speed has increased by a 150 factor!!!
• But what happened at the paranode?
• How is it possible to have a change, from an active mechanism with a low speed to a passive one with a speed multiplied by 150?

[bernard]

8/ The Relativity of an Elastic Train

The duration of an AP is well known and was recorded million and millions times. It is approximately of 2 milliseconds (2 10^-3 s).

When we record an AP, we digitize it with a sampling rate that may 100/5000 less than its duration. This sampling rate gives us a great precision and allows to make computations with recorded data.

The collected data may be view as little wagons of an AP train.
This train is real and the recorded values attest of this reality.

But man, you've said that the train entering the tunnel of myelin is accelerated! It would conclude that wagons leave the train while entering it.
The train must be then dilated and of course, since we have not the same speed at the same time for the whole train, that a part of AP exists with a speed and another must exist with another speed. It is the only possible conclusion since we said that propagation is a continuous phenomenon. (my bold).

Thus, we must have during a small duration, two APs.

[bernard]

9/ Is something wrong with the samples?

I made a little pictures that show the recorded curves at node and at some distances (d₁, d₂, d₃) under myelin.

These APs are not disputable, they were recorded.
It is this marvelous picture that pointed out the flaw in the theory. :lightbulb

ps: the graph is not really good because distances have to be enlarged. I privileged the durations of APs.

[bernard]

10/ Ghost Action Potential

• Same sampling rate
• Different speeds 1/150

=> curve under myelin must be 150 shorter in duration since its speed is 150 faster. The picture below shows the difference!

If we record curves like in the previous picture, it has only one meaning: These action potential are not travelling. They are ghost images of the real AP of the node. They are shadows of something that happens elsewhere.

[bernard]

11/ Shockwave of a Ionic Gun

Since I discard a real existence of propagation but we are still able to record "APs" under myelin without a real deformation of their duration, I must give an explanation:

Nature didn't used the same mean (electrostatic). It used an enhanced mean: An ionic gun!

The bullet powder is the AP at node and the gun is the myelin tube, the bullet itself is the tube content. Simple, economic, quite no motion and because the tube is elastic, we are still able to record the propagation of the shockwave that occurs in a ionic solution with respect of recorded durations.

I'm sure that Jason is an expert about shockwaves. :lightbulb

[bernard]

12/ A Good Start!

Proc Natl Acad Sci U S A. 2005 Jul 12;102(28):9790-5. Epub 2005 Jul 1. Related Articles, Links
On soliton propagation in biomembranes and nerves.

Heimburg T, Jackson AD.

The Niels Bohr Institute, University of Copenhagen, 17 Blegdamsvej, 2100 Copenhagen O, Denmark. theimbu@nbi.dk

The lipids of biological membranes and intact biomembranes display chain melting transitions close to temperatures of physiological interest. During this transition the heat capacity, volume and area compressibilities, and relaxation times all reach maxima. Compressibilities are thus nonlinear functions of temperature and pressure in the vicinity of the melting transition, and we show that this feature leads to the possibility of soliton propagation in such membranes. In particular, if the membrane state is above the melting transition solitons will involve changes in lipid state. We discuss solitons in the context of several striking properties of nerve membranes under the influence of the action potential, including mechanical dislocations and temperature changes.

PMID: 15994235 [PubMed - indexed for MEDLINE]

[BB]

Bernard,
US independence day is July 4th, and a patient was talking with me about fireworks today.

A friend of his lost an eye because he duct taped a bunch of fire crackers together. This constriction, intensified the explosion. The patient said that the same thing happens when you wrap up dynamite with duct tape.

Constriction amplifies the transmission of the force.

Is this the same mechanism you are describing? Myelin is the duct tape? The action potential is a recording of a wave traveling through the liquid properties of the nerve that keeps getting amplified by each myelin sheath which does not allow the wave deformation?

If this is the case, would the wave build speed the further it travelled? Be moving a bit faster at each node as it keeps getting amplified?

Cory

[bernard]

Constriction amplifies the transmission of the force.

Of course, but importance is given in that case to the transmission over long distance. The initial force is very attenuated/damped.

Is this the same mechanism you are describing? Myelin is the duct tape? The action potential is a recording of a wave traveling through the liquid properties of the nerve that keeps getting amplified by each myelin sheath which does not allow the wave deformation?

Myelin is a duct tape that disallows transversal deformation of the membrane. Myelin is not amplifying the wave. An echo is transmitted that allows a new ignition at the next node.

It is the best evil solution because nothing really move far. Economy! Beauty and Efficiency.

I'm amazed BTW that Nature in case of neuron used many solutions at the same time. I'll explain this point of view in the propagation thread.