Saltatory Conduction: single AP or not?

[atyy]

Kole MH, Ilschner SU, Kampa BM, Williams SR, Ruben PC, Stuart GJ. Action potential generation requires a high sodium channel density in the axon initial segment. Nat Neurosci. 2008 Feb;11(2):178-86.

"...It is commonly assumed that this process requires a high density of voltage-gated sodium (Na(+)) channels. Paradoxically, the results of patch-clamp studies suggest that the Na(+) channel density at the AIS is similar to that at the soma and proximal dendrites..."

 

[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.

 

[somasimple]

Yes, the "decay only" idea only gives an effective delay for the onset. Some sort of filtering is needed to get an effective delay in the peak (which is also closer to how H+S defined onset), which is another reason that I should include the time constant to get the internode speed right.

Is your decay+delay curve from model #2 in post #21?

No. These curves are only working hypothesis.
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.
The #2 is closer to our Cm computations for the internode.
http://en.wikipedia.org/wiki/Cut-off_frequency

 

[somasimple]

Kole MH, Ilschner SU, Kampa BM, Williams SR, Ruben PC, Stuart GJ. Action potential generation requires a high sodium channel density in the axon initial segment. Nat Neurosci. 2008 Feb;11(2):178-86.

"...It is commonly assumed that this process requires a high density of voltage-gated sodium (Na(+)) channels. Paradoxically, the results of patch-clamp studies suggest that the Na(+) channel density at the AIS is similar to that at the soma and proximal dendrites..."

Why nobody takes account of a silent phenomenon? : LATENCY. Silent doesn't mean passive. Sub-threshold, too.

 

[somasimple]

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.

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

 

[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.