Membrane potential of a neuron, when it is not transmitting any signal, with respect to its immediate surrounding is called resting potential. Generally the value of resting potential is -70mV.
Resting membrane potential is negative due to: 1. presece of large number of positive Na ions towards outside of membrane 2. presence of smaller number of positive K ions towards inside of membrane 3. zwitterionic protein molecules of cytoplasm behave as negative ions in presence of highly charged K 4. Na-K ion pump continuously pumps out three sodium ions while only two potassium ions are taken inside the cell.
When there is a change in immediate external or internal environment of the body, it acts as stimulus for neuron. Sodium channels open up to allow diffusion of Na inside stimulated area, thereby depolarisation of membrane takes place.
It can be described as reversal of negative membrane potential in positive membrane potential, also called action potential. Impulse transmission can take place only after the development of action potential from resting potential.