Normally, a neurone is not transmitting an impulse and the membrane is at a resting potential of -70mV. The inside of the membrane is more negative than the outside and the membrane is said to be polarised.Sodium ions are actively transported out of the axon and potassium ions actively transported in by the sodium potassium pump. For every three sodium ions pumped out, two potassium ions are pumped in.In addition, the membrane is more permeable to potassium ions as there are some open potassium channels in the membrane. Potassium ions diffuse back out down their concentration gradient.