Describe how action potentials are initiated and transmitted within a neurone, mentioning the appropriate ions and types of ion channels

A stimulus causes a small influx of sodium ions into the cell, leading the cell to become more depolarised or more positive. If this reaches the threshold potential, of about -55 mV, then it will initiate an all or nothing response and an action potential will be generated. Once the threshold potential is reached, voltage gated sodium ion channels open, causing an influx of sodium ions into the cell. This leads to the cell becoming depolarised. Once the membrane potential reaches about +40 mV, voltage gated sodium ion channels close and voltage gated potassium ion channels open, leading to an efflux of potassium out of the cell. This causes the cell to become repolarised as the membrane potential becomes more negative. The membrane potential then becomes hyperpolarised, and the voltage gated potassium ions channels close. After this, the cell gradually reaches the resting membrane potential through the action of the Na+/K+ ATPase pump, actively transporting sodium out of the cell and potassium into the cell, and the leakage of potassium ions across the membrane and out of the cell.