Potential difference across resting membrane is negatively charged. This is due to differential distribution of the following ions.

1. Na+ and K+ ions

2. CO32- and Cl- ions

3. Ca2+ and Mg2+ ions

4. Ca+4 and Cl- ions

(a) The ion gated channels on the neurolemma control the movement of Na+ and K+ ions on both inner and outer side of nerve cell.
Ca2+, CO32-, Mg2+ and Ca+4 ions are not related with nerve excitation rather are involved in other biological functions. Ca2+ ions are related to muscle metabolism where Mg2+ ions act as a cofactor in some reactions.
Cl- ion channels are important for setting cell resting membrane potential, transepithelial salt transport, and the acidification of internal and extracellular compartments.