Explain how the potential difference across the neuronal cell membrane changes during conduction of an action potential

Normal neuronal resting potential is around -70mV - this is maintained by sodium-potassium pumps. When the neuron is stimulated, sodium ion channels begin to open, allowing sodium ions to diffuse back into the cell. As the potential difference begins to increase due to the influx of positively charged ions, voltage dependent sodium channels along the neuron begin to open, and sodium ions flood back into the cell. This is called depolarisation. When the potential difference is around +30mV, the sodium channels close and voltage gated potassium channels open, allowing potassium to diffuse out of the cell and causing the potential difference to drop again (loss of positively charged ions). This is called repolarisation. As the potential difference drops, potassium channels slowly close - however there is a brief period of hyperpolarisation where the potential difference is lower than resting potential due to the incomplete closure of the potassium channels. Once all the ion channels have closed, the sodium-potassium pump returns the cell to resting potential, at which point it is ready to receive another stimulus.