How is an action potential formed when the neurone is stimulated?

When the neurone is stimulated, the Na+ channels open to allow influx of sodium ions down its electrochemical gradient. This makes the inside of the cell less negative. When threshold voltage (-55mV) is reached, depolarisation occurs. This occurs because the cell becomes much more permeable to Na+ ions, so the massive influx depolarises the membrane. When the membrane voltage reaches +30mV, the Na+ channels close and the K+ ion channels open. This causes K+ ions to flow out of the cell, making the cell more negative. This is called repolarisation. The K+ channels are slow to close, and hyperpolarisation occurs, where the membrane voltage decreases to below resting potential. Eventually, K+ channels close and the sodium-potasium pump restores the membrane back to its resting potential.