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I know this is resourceful and sage forum so I hope to clarify my doubts once for all
I've recently started to do some research on electrophysiology and the concept of myelination and saltatory conduction still baffles me.
Needless to say, I know perfectly the mechanics behind AP conduction in non-myelinated fibers. I also know how myelin seems to speed up the propagation velocity of the AP but here come my doubts:
- Myelin increases transmembrane resistance, thus increasing the "length constant" (i.e. avoids the weakening of the passive currents that spread along the axon).
- Myelin decreases the capacitance of the internodal regions, reducing the "time constant" and enabling a faster depolarization of the nodal regions. But ¿WHY? Is not the capacitance of the nodal regions the same as in a "normal" (non myelinated) axons? If the internodal regions are "sealed" (myelin is an insulator), and no AP is generated here, what's the role of a lowered capacitance in this zone?
Note: I understand that a lowered capacitance means that fewer charges need to be moved in order to produce a given potential difference.
I'd be very grateful If anyone could help me with this complicated topic.
Thanks in advance,
L.
