Describe and explain how an action potential is generated

This is a common question, that takes a little while to get your head around. Once you've understood the process, it can be simplified down to a cycle of 3 steps for memory: depolarisation, repolarisation and hyperpolarisation. But first, let's take a more detailed look at how an action potential is generated in axons: 1. When the axon membrane is at a resting state, it is -70mV inside compared to outside, i.e. polarised. This is due to negatively charged proteins within the cell. 2. The membrane depolarises: the membrane potential become less negative (increases above -70mv) with respect to the outside. 3. If the membrane potential reaches the threshold potential of -55mV, voltage-gated sodium ion channels open and many Na⁺ ions enter. As more Na⁺ ions enter, the more positively charged the cell becomes, compared to outside. 4. The potential difference across the membrane reaches +40mV. The inside is now positive compared to theoutside. 5. The Na⁺ ion channels shut and K⁺ ion channels open. 6. K⁺ ions diffuse out of the cell, bringing the potential difference back to negative compared with the outside: repolarisation. 7. The potential difference overshoots slightly, making the cell hyperpolarised. 8. The original potential difference is restored, so the cell returns to its resting state.