Sodium channels, clustered in high density in the axon membrane at the nodes of Ranvier, are responsible for the depolarization phase of the action potential.
channel pattern in their peripheral nervous system, where myelin is intact, is normal, and the sodium channels are, as expected, concentrated at the nodes of Ranvier, while in the central system the channels are not localized at the nodes but randomly scattered.
Moore and colleagues demonstrated morphological changes with injection of BTX in rat peroneal nerve including massive swelling of the axon at the nodes of Ranvier with retraction of paranodal myelin, as well as swelling of unmyelinated axons.