Spike configuration at internode sections of myelinated axon

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Sun Xiaoqing
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Spike configuration at internode sections of myelinated axon

Post by Sun Xiaoqing » Tue Oct 29, 2019 7:41 am

Good day,

I'm using Moore's Model for myelinated axon: https://senselab.med.yale.edu/ModelDB/S ... 851#tabs-1

And there's one thing that I didn't understand: Why there are spike configurations at the internode sections? In myelinated sections, there are no transmembrane currents then why the intracellular potential changes instead of remaining at -65mV?

Thanks in advance!

ted
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Re: Spike configuration at internode sections of myelinated axon

Post by ted » Tue Oct 29, 2019 9:30 pm

The term "spike configuration" will not be understood by neuroscientists. Perhaps you mean "spike waveform"?

Sun Xiaoqing
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Joined: Wed Aug 28, 2019 1:18 am

Re: Spike configuration at internode sections of myelinated axon

Post by Sun Xiaoqing » Wed Oct 30, 2019 7:23 am

Dear Ted,

I used Shape Plot/Time plot to get the "Spike Waveform".

If NEURON uses Cable Equation to calculate voltage potential, when I increased the length of the myelinated section to 20mm, the shape of the "Spike Waveform" got distorted(the time needed for the Spike to get to its maximum value got longer). Why was that?

I'd like to understand the mechanism of NEURON better, thank you for the explanation!

ted
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Re: Spike configuration at internode sections of myelinated axon

Post by ted » Wed Oct 30, 2019 11:04 am

Enthusiasm is good, asking good questions is good, but this thread is quickly becoming an informal short course on cellular neurophysiology plus circuit theory plus physics--all diverging from the primary aim of the NEURON Forum, which is to address questions about NEURON. Anyone else who wants to, is invited to carry the discussion further. My contribution ends with the following:
when I increased the length of the myelinated section to 20mm, the shape of the "Spike Waveform" got distorted(the time needed for the Spike to get to its maximum value got longer). Why was that?
Time to learn about neuronal electrophysiology, or physics, or electronics, or the cable equation itself.
Why there are spike configurations at the internode sections? In myelinated sections, there are no transmembrane currents then why the intracellular potential changes instead of remaining at -65mV?
Think about Maxwell's equations, or circuit theory. Read something about cable theory--any of Rall's articles. Read something in a decent textbook, like Johnston, D. and Wu, S.M.-S. Foundations of Cellular Neurophysiology. Cambridge,MA: MIT Press. Read the relevant entries in the Encyclopedia of Computational Neuroscience https://link.springer.com/referencework ... 614-7320-6. Take a course on cellular neurophysiology.

Sun Xiaoqing
Posts: 32
Joined: Wed Aug 28, 2019 1:18 am

Re: Spike configuration at internode sections of myelinated axon

Post by Sun Xiaoqing » Fri Nov 01, 2019 8:16 am

Dear Ted,

Thank you so much for the reference book, love the clear explanations. I truly appreciate your help all along!

ted
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Re: Spike configuration at internode sections of myelinated axon

Post by ted » Fri Nov 01, 2019 2:11 pm

In myelinated sections, there are no transmembrane currents then why the intracellular potential changes instead of remaining at -65mV?
Here's a hint at an answer:
The cytoplasm in the myelinated internode acts like a resistor that the flow of current from one end of the internode to the other. According to Ohm's law, if the electrical potentials at the two ends of a resistor are V1 and V2, then the current that flows through the reisistor from one end to the other is
I = (V1 - V2)/R
where R is the resistance of the resistor. If I equals 0, what can you say about V1 and V2?

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