Two factors influence the velocity of action potential propagation along neuronal axons: (1) axon diameter, and (2) myelination. Action potential propagation (or conduction) velocity is directly correlated with the axon diameter. The larger the axon diameter, the higher the action potential propagation velocity will be. In addition, myelination, which leads to salutatory conduction of action potentials along axons, greatly increases the action potential propagation velocity. Despite having much smaller diameters, myelinated axons achieve much higher action potential propagation velocities than do unmyelinated axons. Note the differences in the action potential velocity (y-axis) and axon diameter (x-axis) scales of the two plots. The left plot shows action potential velocity values for unmyelinated axons, and the right plot shows action potential velocity values for myelinated axons.