Explain how an action potential is generated. Sodium ion channels on one end of an axon suddenly open to allow the accumulation of positive sodium ions, making the voltage on that end positive, creating a length‑wise imbalance in the potential with the opposite, negative end. A group of positive potassium ions collects next to an axon, inducing a positive potential on the axon surface. The positive potassium ions suddenly disperse, making the potential on the axon surface suddenly flip sign. When the negative potential inside an axon becomes slightly less negative, sodium ion channels open, allowing positive sodium ions to rush into the axon, flipping the internal potential to a positive value. Potassium channels of an axon suddenly open to allow positive potassium ions to rush out of the axon. When enough leave, the potential inside the axon becomes negative, and the potassium ions rush back in, flipping the potential.