In both myelinated and not-myelinated axon segments ("axons" for short) there are theoretically maximal distances of voltage-gated ion channels beyond which propagation of the action potential would break down because the potential arriving at the next ion channel would be too weak to open it. (In myelinated axons it's about the distance between the nodes of Ranvier.)

In not-myelinated axons this distance is smaller, in myelinated axons it is greater.

Compared to these theoretically maximal distances there are the real distances between the ion channels (smaller for non-myelinated axons, greater for myelinated axons), resp. their mean distance along the axon.

My question is: How strongly do the real (mean) distances of ion channels deviate from the theoretically maximal ones? An axon with greater mean distance than the maximal one would not work very well, an axon with a significantly (and unnecessary) smaller mean distance would waste resources and would possibly produce distracting interferences.

Side question: What's "the" standard deviation of the mean distance of ion channels (nodes of Ranvier)? ("The" because there may be differences between types of neurons/axons.) Are there numbers available?

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    $\begingroup$ Cool question. I don't know if anybody looked into this. Keep in mind that the variability in the action potential and state of the axon will degrade the reliability if set exactly at the theoretical optimum assuming no such variability. $\endgroup$ – Memming Sep 7 '17 at 14:05
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    $\begingroup$ It is a cool question... but I don't think it's answerable. We'd have to study a given neuron (potentially in a given species) with a given number of sodium channels per node, a given radius, etc... at which time you could do experiments and/or calculations. If you fail to take these factors into consideration, each local "spike" will vary in how much it can effect the next node and the "maximum distance" will be subject to a large variation. For example, in a larger neuron, the sodium has more space to diffuse cross-sectionally, leaving less sodium to diffuse laterally. $\endgroup$ – rotaredom Jan 7 at 1:06
  • $\begingroup$ @rotaredom It may be answerable if that research has already been done. $\endgroup$ – user45969 Jan 12 at 13:41

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