I was recently looking over some textbook material (pdf) which claimed post-ganglionic fibers of the sympathetic nervous system are unmyelinated. This was surprising to me, since I had previously thought that long distance transmission of an action potential required myelin (I can even remember being told that myelin was essential for large life forms, because the nerves otherwise could not have controlled distant body parts).

First, is the textbook correct? Second, assuming it is true that post-ganglionic fibers are not myelinated, is there some advantage to this arrangement? At the very least, I would think it would be far more energetic to send a signal in a unmyelinated axon.


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