Action potential speed

[howtomedicine]

I'm reading how once an action potential is initiated in neuron, it will propagate to the end of the axon at a speed and magnitude of depolarization that do not vary from one action potential to the other. However, having a myelin sheath will increase the speed of the action potential. Could someone clarify this for me.

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[TheLongGame]

Neurons function in a "all or nothing" capacity. A stronger stimulus doesn't make the neuron fire faster or stronger, instead more neurons trigger their AP.

Myelin sheaths can be thought of as insulation. In an unmyelinated neuron, the transmission of depolarization must trigger at each NaK pump and associated channels even though the depolarization wave can actually trigger a gate/pump further down the line. Myelin essentially prevents ion exchange with the external axon environment except at the Nodes of Ranvier where the sheath is absent. In this way, the AP can essentially "jump" down the axon at a much faster rate.

Think of it this way. If two axons are of equal length/thickness and the reaction times of the NaK pumps and gates are all equal: the axon with fewer NaK and gate actuations will conduct the signal faster. Myelin essentially minimizes the number of usable pumps and gates to the minimum required, thereby increasing its speed.

Hope this helps!

-Adam


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