Final answer:
The incorrect statement about action potentials is that they all travel at the same speed. Myelination and axon diameter affect the propagation speed of action potentials.
Step-by-step explanation:
The statement that is NOT true of action potentials is that they all travel at the same speed. This is false because in myelinated axons, propagation is described as saltatory conduction and is faster than the continuous conduction found in unmyelinated axons. Additionally, the diameter of the axon influences the speed of action potential propagation, with a larger diameter facilitating faster travel of ions within the axon. Action potentials are indeed electrical charges that shoot down the axon, they are generated according to an all-or-none principle, and they are initiated when the axon is depolarized sufficiently.