Describe and explain how an action potential is generated (6 marks)

The membrane is at resting potential, -60mV inside compared to outside. It is polarised. 2. Na+ ion channels open and some Na+ ions diffuse into the neurone. 3. The membrane depolarises- it become less negative with respect to the outside and reaches the threshold potential of -50mV. 4. Voltage-gated sodium ion channels open and many Na+ ions enter. As more Na+ ions enter, the inside of the cell becomes more positively charged compared to the outside. 5. The potential difference across the membrane reaches +40mV. The inside is now positive compared to the outside. The Na+ ion channels shut and the 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 potential.