neurologic disorders
Neurotransmission
Propagation
Action potential propagation along an axon is electrical, caused by the exchanges of sodium and potassium ions across the axonal membrane. A particular neuron generates the same action potential after each stimulus, conducting it at a fixed velocity along the axon. Velocity depends on axonal diameter and degree of myelination and ranges from 1 to 4 m/sec in small unmyelinated fibers to 75 m/sec in large myelinated ones. Propagation speed is higher in myelinated fibers because the myelin cover has regular gaps (nodes of Ranvier) where the axon is exposed. The electrical impulse jumps from one node to the next, skipping the myelinated section of the axon. Thus, disorders that alter the myelin cover (eg, Multiple Sclerosis (MS) , 