Biology A-level: describing the action potential

At rest K+ that is going out of cell clamps the membrane potential negative (e.g. -70 mV)An external factor (e.g. synaptic activity) causes the membrane to depolarise slightly. If the voltage reaches threshold, thenNa+ conductance shoots up, Na+ current goes into cell, membrane potential depolarises (With a time-delay, Na+ conduction diminishes (inactivation), K+ conductance increases, so K+ leaves cell, voltage returns to resting potential (i.e. the membrane repolarises)