English: Key:
(a) Sodium (Na+) ion
(b) Potassium (K+) ion
(c) Sodium channel
(d) Potassium channel
(e) Sodium-Potassium Pump
In the stages of an action potential, the permeability of the membrane of the neuron changes. At the resting state (1), sodium and potassium ions are unable to pass through the membrane, and the neuron has a negative charge inside (mainly due to the large proteins that are negatively charged, as well as the lower amount of positive K+ ions inside the neuron). Once the action potential is triggered, the depolarization (2) of the neuron activates the sodium channel, allowing sodium ions to pass through the membrane of the neuron and results in a positive charge in the neuron and a negative charge in the extracellular fluid. After the action potential is reached, the neuron begins repolarization (3), where the sodium channels close and the potassium channels open, allowing potassium ions to cross the membrane and flood into the extracellular fluid, resulting in a positive charge in the extracellular fluid and a negative charge that is below the resting potential of the neuron. Finally, the membrane potential returns to the resting state as the potassium channels close during the refractory period (4). The sodium-potassium pump works to maintain the concentration gradient over time by exchanging three sodium ions per two potassium ions across the plasma membrane .
https://www.youtube.com/watch?v=UabDiuTtU0M
https://www.youtube.com/watch?v=UabDiuTtU0M