English: An annotated diagram of the stages of an action potential propagating down an axon including the role of ion concentration and pump and channel proteins.

Transcription: (Top to bottom, left to right)

First Section:
Title: Resting Potential
Labels: Sodium ions (Na⁺), Sodium Ion Channel Protein, Sodium/Potassium Pump Protein, Potassium Ion Channel Protein, Potassium ions (K⁺), Phospholipid Bilayer

Second Section:
Title: Rising Phase
Caption: The action potential propagates down the axon, increasing the positive ion concentration, and thereby the voltage. This activates the voltage gated sodium ion channels, which open, causing ions to fall down their concentration gradients, flowing in. This increases the ion concentration around the channel and opens nearby voltage gated sodium ion channels.

Third Section:
Title: Falling Phase/Depolarization
Caption: As ions flow into the axon, eventually they reach a high enough concentration that the voltage gated sodium channels close and the voltage gated potassium channels open. This allows the potassium to fall down its concentration gradient, decreasing the number of ions in the axon and lowering the voltage.

Fourth Section:
Title: Afterhyperpolarization/Repolarization

Caption: As potassium ions flow out, the number of ions on the inside of the axon, and therefore the voltage, decreases. This eventually causes the voltage gated potassium channels to close. Then, ATP is used to power a potassium/sodium ion pump, pushing the sets of ions back to their original sides, returning the axon to its resting potential state.