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Saltatory Conduction: single AP or not?

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somasimple
#163
Oct4-08, 03:57 PM
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No, DaleSpam
You're only taking me for an idiot.
http://www.myreckonings.com/wordpres...eEquations.jpg
Please are you able to record such a signal in a cable or an axon? Just no!
Every time you are faulty you bring an obscure statement or function that has no relation with the discussion.
As I said it earlier you are not obliged to try to reply systematically in opposition: That is not a scientific behavior...
Goodbye you had already proved your... talent.
granpa
#164
Oct4-08, 07:37 PM
P: 2,258
I'm afraid dale is right. this has become tiresome. you shoot down anything I say while making vague cryptic references to some theory of yours that you never bother to explain. I dont even know what it is that you are arguing and this is page 9. really enough is enough.
atyy
#165
Oct4-08, 08:15 PM
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Points in this post are my interpretation of: Ritchie, Physiology of Axons in "The Axon: Structure, Function and Pathophysiology" ed. Waxman, Kocsis and Stys, OUP 1995.

1. Myelinated axons conduct faster (v~d) than unmyelinated axons (v~sqrt(d)), where v is the speed across nodes and internodes. The key for this is the length constant, as I suspected from dimensional considerations in earlier posts. (Lussier and Rushton 1951).

2. There are references for the computation of velocity in axons, but I do not know whether this is across nodes and internodes, or whether they can also compute a separate internode velocity. (Blight 1985, Brill et al 1978, Dodge 1963, Fitzhugh 1962, Goldman and Albus 1968, Hardy 1973, Hutchinson et al 1970, Koles and Rasinsky 1972, Moore et al 1978, Ritchie and Stagg 1982, Schauf and Davis 1974, Waxman and Brill 1978, Wood and Waxman 1982)

3. There is criticism of the "classical" passive internode model and the neglect of a conduction pathway beneath the myelin, especially for mammalian myelinated axons. (Barrett and Barrett 1982, Blight 1985, Blight and Someya 1985, Bowe et al 1987). Quote for somasimple: "The internodal membrane not only has a capacitance two to three orders of magnitude greater than that of the node, but also contains a repertoire of ionic conductances...".

4. There is criticism of Rushton's analysis for small myelineated axons: "Rushton's belief that conduction velocity of PNS myelinated nerve fibers falls off markedly ... may be correct, but perhaps for a different reason from the one he proposed..."

5. "The studies of Moore et al (1978) show that internodal parameters control the conduction velocity far more than does the node itself. They help account for the insensitivity to the nodal constriction that is characteristic of myelinated fibers."

6. "[referring to activation rate constants] Why this should be so is unclear. Indeed it should be pointed out that the conduction velocity of a mammalian nerve fiber at 37oC can be simulated reasonably well only if these activation constants are brought into line with the squid giant axon value of 3 (Ritchie and Stagg 1982)."
atyy
#166
Oct4-08, 08:17 PM
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Hi somasimple, I'm done with the discussion too - but I think your points are excellent. This is really getting into specialist territory, and I'm not personally inclined to pursue the details further. Much luck on your studies!
somasimple
#167
Oct6-08, 12:07 AM
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Quote Quote by granpa View Post
I'm afraid dale is right. this has become tiresome. you shoot down anything I say while making vague cryptic references to some theory of yours that you never bother to explain. I dont even know what it is that you are arguing and this is page 9. really enough is enough.
The content of this thread was started to elucidate if 2 or more nodes are active during a single message propagation. This is a complex subject and solitons are much more complex.
You question about inductance, water... are far out the subject.

Atyy,
Thanks for the support.
I'll take a closer look at references.
ps: the Koch's book is disappointing: it contains quite nothing on the subject.
BTW, it gives more numbers and some graphs show strange results...
somasimple
#169
Oct7-08, 12:13 AM
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Interesting concepts but what is the relation with the current subject?
granpa
#170
Oct7-08, 12:22 AM
P: 2,258
no particular relation. just showing that ions and electric fields can and do interact with phonons. hence the possibility of an electrical signal propagating at the speed of sound.
somasimple
#171
Oct7-08, 12:50 AM
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But we're working, here, in a wet and hydrated environment, not a crystalline one.
somasimple
#172
Oct7-08, 09:02 AM
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http://stbb.nichd.nih.gov/role_pot_wave52.pdf

The action current of a conducted nerve impulse changes its shape when the
recording partition is shifted along the nerve fiber. Within an internodal segment,
the rising phase of the action current is shortest and the maximum is attained earliest
when the recording partition is located at the proximal end of the internode. The
rising phase is retarded, within an internodal stretch, continuously with increasing
distance of the recording partition from the proximal node
. This fact is also ascribed
to the distributed capacity of the myelin-covered portion of the nerve fiber.
The difference between the time-course of the action current (flowing through
the axis-cylinder) and that of the action potential (recorded from the surface of the
nerve trunk) is shown to be due to the capacity distributed along the surface of the
nerve fiber.
The latent period of the action potential of a conducted nerve impulse varies
continuously as the distance along the fiber. The steepnes so f the rising phases hows
a sharp maximum at each node of Ranvier regularly. This result was correlated
with the measurements of action currents recorded by the partition method.
Conduction of the nerve impulse in myelinated fibers is saltatory with respect to
space but not, in general, with respect to time
.


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