Saltatory Conduction: single AP or not?

[granpa]

We have had already discussed about these instructive curves but DaleSpam contests any delay in the internode.
For my own, I accept facts.

you mean delay at the nodes?

 

[somasimple]

A delay at nodes may be the result of combined delays:

1. Latency (but I suspect that an axon skips it.)
2. Delay in the internode (from records).
3. Delay implied by decay.

 

[granpa]

http://www.pubmedcentral.nih.gov/pagerender.fcgi?artid=1392492&pageindex=8

it appears to me based on this that the ap from one node passes right through the next node without delay but has become by that time so spread out that it just appears to be the onset/upstroke of the next ap which actually occurs (at that next node) after a 0.1 ms delay.

 

[somasimple]

http://www.pubmedcentral.nih.gov/pagerender.fcgi?artid=1392492&pageindex=8

it appears to me based on this that the ap from one node passes right through the next node without delay but has become by that time so spread out that it just appears to be the onset of the next ap which actually occurs (at that next node) after a 0.1 ms delay.

The B curve shows stairs that aren't horizontal => Delay.

 

[granpa]

further the speed through the internode appears to be so fast that it can't even be determined from the graphs. the measured 20 m/s being due almost entirely to the delay at each node.

 

[granpa]

The B curve shows stairs that aren't horizontal => Delay.

what do you figure the speed is?

 

[somasimple]

further the speed through the internode appears to be so fast that it can't even be determined from the graphs. the measured 20 m/s being due almost entirely to the delay at each node.

A speed may be seen as fast when you compare it with a slow one.
The delay is around 20 µs (internode to internode). You have not records from nodes so you can't extrapolate that way.

 

[somasimple]

what do you figure the speed is?

800 to 1300 ms-1
perhaps less.

 

[granpa]

800 to 1300 ms-1
perhaps less.

sounds about right. speed of sound in water being 1500 m/s

 

[granpa]

The B curve shows stairs that aren't horizontal => Delay.

whoa. I totally misunderstood you. I thought you were saying the horizontal parts of the B curve weren't really horizontal.

you also misundrestood me. when I said it (the B curve) seems to pass through without delay I mean it seems to become the A curve

 

[somasimple]

whoa. I totally misunderstood you. I thought you were saying the horizontal parts of the B curve weren't really horizontal.

you also misundrestood me. when I said it (the B curve) seems to pass through without delay I mean it seems to become the A curve

The A curve is based upon rising phases that vary with decays.
Average speed must be < 1500 ms-1 because of the dampening (decay).

Edit: I said it =>

I thought you were saying the horizontal parts of the B curve weren't really horizontal.

 

[granpa]

maybe you've seen this before but this is really interesting:

http://www.pubmedcentral.nih.gov/pagerender.fcgi?artid=1392492&pageindex=7

and especially this:

http://www.pubmedcentral.nih.gov/pagerender.fcgi?artid=1392492&pageindex=8

the peak seems to move almost instantly the 2 mm from node to node (the amplitude decreasing to not quite half) with a considerable delay (slightly less than 0.1 ms) at each node which gives it a net speed of 20 m/s. (during the internode, wouldn't it have to be moving at or very close to the speed of sound?) (which is 1500 m/s in water)

after the delay, the beginning of the peak at one node coincides with the beginning of the downstroke of the previous internode. which actually seems to move backward.


the arrival of the peak at the node at the end of one internode seems to correspond to the beginning of the upstroke of the next internode.

notice what I said about the C curve too.

 

[somasimple]

which actually seems to move backward.

This?

 

[granpa]

The A curve is based upon rising phases that vary with decays.
Average speed must be < 1500 ms-1 because of the dampening (decay).

Edit: I said it =>

I don't see your first point.

so it can't be a sound wave becaise it decays? hmmmm.

 

[granpa]

This?

this what?

 

[somasimple]

this what?

which actually seems to move backward.

so it can't be a sound wave becaise it decays? hmmmm.

Sound is a wave and it strength decays with distance.
A wave is a wave, so...

 

[somasimple]

If the node is purely passive as expected you must have a backward effect:

Here is a simple working hypothesis:
The movie is not completed.
www.somasimple.com/flash_anims/node_01.swf

 

[granpa]

oh. yes, that is what I was referring to.

I'll try to watch your animation but my competer tends to freeze whenever I do.

 

[granpa]

but the backward effect is the opposite of what you would expect. it returns the axon to its resting state.

 

[somasimple]

oh. yes, that is what I was referring to.

I'll try to watch your animation but my competer tends to freeze whenever I do.

Update your flash player;
http://www.adobe.com//downloads/

 

[somasimple]

but the backward effect is the opposite of what you would expect. it returns the axon to its resting state.

Hmmm, no, it implies an effect we do not see on curves.

 

[granpa]

thanks. I did get to see it. I watched for about 20 seconds. it just repeats doesn't it?

 

[somasimple]

Update your flash player;
http://www.adobe.com//downloads/

or download it on your computer.

 

[granpa]

that is exactly what I would have expected but like I said the backward effect is exactly the opposite.

 

[somasimple]

thanks. I did get to see it. I watched for about 20 seconds. it just repeats doesn't it?

Yes it repeats. Just a working hypothesis to see the transition phases.

 

[somasimple]

that is exactly what I would have expected but like I said the backward effect is exactly the opposite.

If you do not see the expected prediction of a theory, change the facts or theory.

 

[granpa]

If you do not see the expected prediction of a theory, change the facts or theory.

hmm. facts or theory. hmmm

 

[granpa]

http://www.pubmedcentral.nih.gov/pagerender.fcgi?artid=1392492&pageindex=8

imagine this: four nodes. nodes 1,2,3 and 4. nodes 3 and 4 would be locked (all nodes would normally be locked). meaning they won't pass signals. the first signal that reaches node 3 is from node 1. it has the effect of unlocking the node. this would take time so there would be a delay before node 2 fires. node 2 then fires and the ap passes through node 3 (without delay) to node 4 which it unlocks. there is a delay while node 4 is being unlocked. then node 3 fires.

just before each node fires it locks itself again. so when it does fire the ap can only go in one direction.

so the sequence for each locked node would be:
1 receive a weak signal from 2 nodes away that unlocks it
2 pass, without delay, a stronger signal from 1 node away to unlock the next node.
3 lock itself and then fire its own ap.

the point of course would be to prevent misfiring. this would explain why there is such a long and seemingly needless delay at each node.
and after each node locks itself the previous internode can begin to return to its resting state. hence the backward moving anti-action-potential I mentioned. (anti not because it is moving backword but because it returns the axon to its resting state)

 

[atyy]

We disagree how is the passive section and what is happening.

What is the disagreement? Model #2 in your post 21, and DaleSpam's cable equation seem to be basically the same, and Huxley and Stämpfli seem to mention both for the internode:

HS p329 cf Model #2: "length of a fibre which does not include a node is closely similar to ... a resistance and capacity in parallel...".

HS's p333 cf cable equation: the bottom equation has a second order derivative in space, and first order derivative in time.

The models are two low pass filters and only the cutoff frequency will be changed without any phase change for such a signal. NO DELAY.[/url]

Don't RC circuits have frequency dependent phase shifts? Also, the time course of a signal depends on the presence of all its Fourier frequencies, so wouldn't a frequency dependent reduction in amplitude (even without a phase shift for each Fourier component) produce a shape change in the time course anyway?

The passives sites must exhibit what the active are doing in both directions because they are passive.

after the delay, the beginning of the peak at one node coincides with the beginning of the downstroke of the previous internode. which actually seems to move backward.

If the node is purely passive as expected you must have a backward effect

HS discusses how the backward effect is seen in their data (p323): "surprising feature that the descending phase occurs earlier at the distal than at the proximal end of the internode ... Graph C in one internode and Graph B in the next more distal internode represent different aspects of the same disturbance spreading symmetrically from the node separating them.

 

[somasimple]

What is the disagreement?

Delay in the internode propagation.

a resistance and capacity in parallel...

This does not tell us how they are connected.
Why the capacity is omitted since it is 40 time greater than at node?

Don't RC circuits have frequency dependent phase shifts? Also, the time course of a signal depends on the presence of all its Fourier frequencies, so wouldn't a frequency dependent reduction in amplitude (even without a phase shift for each Fourier component) produce a shape change in the time course anyway?

Phase shift is not equal to delay.
BTW, the better way to test such models is sinusoidal signals.

surprising feature that the descending phase occurs earlier at the distal than at the proximal end of the internode

Graph it! It seems normal with a decay. (see the pictures I provided)

Granpa,
Make a drawing: I'm lost.

 

[somasimple]

http://www.pubmedcentral.nih.gov/pagerender.fcgi?artid=1392492&pageindex=9#page
This comes from page 323:

This spread takes place with a finite velocity (not necessarily constant) so that graph B becomes later, and graph C earlier towards the distal end of each internode.

Ditto!
An attenuation that occurs with distance must take time.

 

[somasimple]

Granpa,
Make a drawing: I'm lost.

imagine this: four nodes. nodes 1,2,3 and 4. nodes 3 and 4 would be locked (all nodes would normally be locked).

Hmmm, no: It is better to lock something to ensure the transmission. Locking something before the transmission will be the best source of problem and no transmission.

 

[Dale]

A theory must describe all facts and make logical links between them. ... Why are you reducing the field of discussion?
Sub-threshold activity, as the whole cable theory, describes a facet of a thing that has many others.

This is completely wrong. Each scientific theory has some limited domain of applicability. For example, Maxwell's equations do not model the orbits of planets nor does it model the photoelectric effect, such things are outside of its domain. Maxwell's theory of EM does not need to "describe all facts", it only needs to describe and link facts within its domain. The search for a "Grand Unified Theory" or "Theory of Everything" is ongoing, and even if such a theory were available it would likely be too cumbersome to apply to neurons.

The domain of cable theory is sub-threshold activity, it always has been. Did you not understand that? The HH model describes supra-threshold activity and does not include any propagation mechanism. The cable model includes a propagation mechanism, but does not describe supra-threshold behavior. I thought that was understood, perhaps this is the real problem.

Please choose the electric model that mimics this activity and give us some values?
I understand why you continuously refuse...
Langauge barrier? I do not think so.

I have told you the model I support several times: the standard HH model and cable equation. Since these are the standard models used my mainstream scientists there are plenty of references describing in exhaustive detail their use and their experimental validation. You know that perfectly well since you have read many of these papers. What could I possibly put in a post than would be more informative that what you already have read? I have neither the time nor the inclination for such a pointless pursuit.

 

[somasimple]

I have neither the time nor the inclination for such a pointless pursuit.

That is not a problem. I have the same inclination.

 

[somasimple]

The HH model describes supra-threshold activity and does not include any propagation mechanism.

http://en.wikipedia.org/wiki/Hodgkin-Huxley_model

The Hodgkin–Huxley model is a scientific model that describes how action potentials in neurons are initiated and propagated. It is a set of nonlinear ordinary differential equations that approximates the electrical characteristics of excitable cells such as neurons and cardiac myocytes.

(sic)!