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Passive Spread Current (continued)

  1. Sep 17, 2008 #1

    somasimple

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    https://www.physicsforums.com/showpost.php?p=1876004&postcount=49

    You must consider the two other curves even if they contradict the cable theory.

    The shapes change under the myelin I didn't took this case in example and I do not contest the fact that the signal is dampened with distance. They recorded every 0.1 mm (100 µm). A node is 1µm wide. This is source of error (and they explained it in the paper).

    You can give your values for the components of the circuit. We will be in agreement.

    ps: That is the second time the treads I started are closed without any advice and any rules violation from my own.
     
  2. jcsd
  3. Sep 17, 2008 #2

    somasimple

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    The paper tells us clearly that they recorded a point at a time. A great patience for these pioneers. Then, they computed the data and obtained the graphs A, B and C.

    The graph I provided is a simultaneous recording at several nodes and it is in agreement with the collected data and conduction velocity.
     
    Last edited: Sep 17, 2008
  4. Sep 17, 2008 #3

    atyy

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    It's too bad they closed your other thread. I thought your questions were excellent.

    For the sake of clarity, could you restate your question, so that we have a well-defined issue to discuss?
     
  5. Sep 17, 2008 #4

    somasimple

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    About the car or an electric signal:
    http://www.grc.nasa.gov/WWW/K-12/airplane/conmo.html

    The mass of an AP may be, by example, its integration.
    Even if the shape changes under the myelin, this change is minor in constrast of its velocity.
    So you get this:
    Q1 quite egal to Q2
    Vnode*Q1<<< Vinternode*Q2.
    The cable theory predicts a passive event under myelin.
     
    Last edited: Sep 17, 2008
  6. Sep 17, 2008 #5

    somasimple

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    Here is a new graph:

    I plotted the conduction velocity in red.
    I centered the APs, at nodes, on this line.
    Each quite horizontal segment is the internode event.

    The blue region shows all active nodes (n2, n3, n4 and n5) when AP at node 2 (n2) exists.

    Do you agree?
     

    Attached Files:

    Last edited: Sep 17, 2008
  7. Sep 17, 2008 #6

    atyy

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    What do the brown lines in the internode region represent (which part of the internode event)?

    Could you give the details of your reasoning (step by step) - which figure/data in their paper did you use, and how did you use it, to obtain the lines in your figure.

    Also, which part in particular are we suppose to examine - give us more guidance about what your question specifically is other than "Do you agree?". What in their data or the theory about their data is puzzling you?
     
    Last edited: Sep 17, 2008
  8. Sep 17, 2008 #7

    atyy

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    Take a look at Fig 10. Their text on that figure includes the comment "In order to see whether the transition between the two forms of action potential takes place as predicted ..." (p325).

    Evidence for saltatory conduction in peripheral myelinated nerve fibres
    A. F. Huxley and R. Stämpfli
    http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1392492
     
  9. Sep 17, 2008 #8

    somasimple

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    The brown lines are the events that may happen under the myelin. (I made them brown to show a kind of discontinuity).
    The blue ones are the APs recorded at nodes.
    All values were rounded ( see fig 7 => APs are shortened by lines) to make a simpler figure.

    Values on horizontal axe are distances and time are plotted as vertical values.

    The figure 10 shows the problem I told you earlier: The sampling distance may change the AP shape around nodes.

    The red line shows the conduction velocity.
    It seems reasonable to plot APs (at nodes) separated by 2 mm (from their graphs) ?
    It shows that following Ap is well initiated when the previous reaches a good value.

    The blue transparent zone shows active nodes that occur during a single AP (node 2).
     
    Last edited: Sep 17, 2008
  10. Sep 17, 2008 #9

    atyy

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    I am referring to H&S's Fig 7 in my comments on your next 3 quotes.

    That looks ok.

    That looks ok too, taking the nodes to be the "jumpy bits" of their plots.

    Plots A,B,C respectively represent the start, peak and end of the AP.

    At t=0.5, the A curve is at node d=3 and the B curve is at node d=1, so the AP at node d=3 begins in the middle of the AP at node d=1. So yes, the AP at the next node is initiated in the middle of the AP at the previous node.

    Now looking at node d=1, the AP starts at t=0.4 and ends at t=0.7. Draw horizontal lines at t=0.4 and t=0.7 across the whole figure, and count the number of jumpy bits between them to be 4, which is about the same as what you plotted.

    Good.

    I really don't understand what your question is - do they say it changes shape but you don't think it does - or do they say it doesn't change shape but you think it does? Or do you think they interpreted their data incorrectly?
     
  11. Sep 17, 2008 #10

    Dale

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    I have to partially agree with somasimple here. Since somasimple's posts are in direct disagreement with mainstream science it is not surprising that his threads get closed, but it would help if the moderator who locks a thread give the justification.
     
  12. Sep 17, 2008 #11

    somasimple

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    The position of the electrodes implies automatically the modification of the shape near the nodes.
    They do not interpret incorrectly their data with their theory. I just want to show some aspects that were not discussed.
     
  13. Sep 17, 2008 #12

    Dale

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    Certainly, but similarly you must consider the experimental data even if they support the cable theory, which they do.

    So if you agree with that part of cable theory then what part of cable theory do you disagree with? So far you agree with a key prediction of the cable theory (passive signal dampened with distance) and your objection (AP spatial length is greater than the space constant) is not a prediction of the theory.

    Electrical signals are not massive, they are not rigid, they do not have momentum, and they do not have inertia. Their velocity can change without force and their shape can change without stress. Your continued analogies in this direction are not helpful to your argument.
     
  14. Sep 17, 2008 #13

    atyy

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    -Good!
    -Their discussion is already very complex, and one certainly shouldn't agree with all aspects of their discussion without intensive study, and examination of more recent data. Hodgkin and Stämpfli themselves note that some of their inferences are indirect, and that not all experimental evidence available at that time was unanimous.
    -The major point is saltatory conduction, and that appears to be easily substantiated by their data, at least on quick perusal.
    -They discuss whether the nodes and internodes are active or passive, and conclude that it is a good approximation to describe the nodes as active and the internodes as passive, but they do not rule out improvements or corrections to this idea.

    That means you are discussing very fine points! Excellent! But I will probably not be able to comment without reading their paper and more current literature carefully, so please take no offense if I don't comment. Hopefully someone else will be able to discuss such issues.
     
    Last edited: Sep 17, 2008
  15. Sep 17, 2008 #14

    somasimple

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    Agreeing with recorded facts is just a question of reason but it doesn't imply that I'm agreeing with the whole theory.
    BTW, quite all domains of Physics exhibit phenomenons that fade with distance or time. You can't discard this eventuality before you examined the other possible solutions.

    May I rephrase the content of the graph like this?

    With
    n=2, k=0.3, v=23,
    A myelinated axon has a known conduction velocity of v
    When the amplitude of an AP, that occurs at a node n and with a duration of k milliseconds, reaches the value of propagation, it triggers a transient event that has a very short duration (few µs). This very short event initiates a AP at node n+1 ans so on...
     
  16. Sep 17, 2008 #15

    somasimple

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    A typo was made in the last sentence; ans so on => and so on...
     
  17. Sep 17, 2008 #16

    Dale

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    Yes, I know that you do not agree with the whole theory. What I don't know is which parts of the theory you disagree with.
    Are you just trying to restate the data or are you trying to place it in the context of a theory? If you are just restating the data then you shouldn't make any claims about what is happening at a node since only inter-node data is presented. If you are placing the data in a theoretical context then I don't know what you mean by "transient event". In the standard theory the passive "cable" conduction is always happening, and the active AP takes several tenths of a ms at each point.
     
  18. Sep 17, 2008 #17

    somasimple

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    Great, you have introduced the notion of Continuity. I take it.

    About extrapolations;
    At node: What is the speed of an event that has a duration of 0.3 ms and travels 1 µm?
    For internode : What is the speed of an event that has a duration of 10 µs (or less if you want) and travels 2 mm?
     
  19. Sep 17, 2008 #18

    Dale

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    Before we continue can you clearly state which part of the standard theory you disagree with?

    This is now the third time I have had to ask this question just since you began this new thread. It is pointless to continue until you clearly define your objection.
     
  20. Sep 17, 2008 #19

    atyy

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    The "event" that you define to travel in the internode would correspond roughly to a fixed "phase" of the AP. Because the AP is changing shape and decaying in the internode, and also because a passive cable has no travelling wave solutions, the "phase" of an AP in the internode in cable theory can only be indirectly defined.

    I think we shouldn't compute the "real" travel speed in the node - at least not from (AP duration)/(node length) because that would use different phases of the AP.

    In one of your one of your posts on the orginal thread, you treated the node as a point, which seems a reasonable approximation (https://www.physicsforums.com/showthread.php?t=254044).

    So a rough picture could be as follows:
    1. AP speed across nodes and internodes is about 20 mm/ms.
    2. Nodes are spaced 2 mm apart.
    3. In the internodes, travel is passive and very fast, so we may take the travel time in the internodes to be roughly 0 ms.
    4. However, the AP changes shape and decays in the internodes.
    5. The AP has to be actively re-boosted at nodes.
    6. Most of the "travel time" is actually time spent re-boosting the AP at a node ~ 2/20 ms = 0.1 ms.
    7. In your post #5, the brown line representing the "internode event" begins at ~0.1 ms after the start of an AP, in accord with the above.
     
  21. Sep 18, 2008 #20

    somasimple

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    http://www.greenandwhite.net/~chbut/conservation_of_momentum.htm
    Example: compute the necessary energy to promote an electric signal from 0 mV to 0.001mV within 0 ms! A short event duration hides often a high energy...

    NO! Electric signals may have work and power. Your statement implies an infinite velocity => d/t
    Energy/momentum and the graph I provide (where you agreed) implies a solution of continuity (discontinuity) in the electric signal. I can demonstrate it.
    Please give me some values for a simulation as I asked already earlier. (unmeylinated and myelinated axons).
    Thanks, you confirm my point of view.
     
    Last edited: Sep 18, 2008
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