1. Resting membrane potential : Plasmamembrane of axon of neuron has +ve charge on outer surface and –ve charge on interior side, this electrical potential across the membrane is called resting membrane potential.

When a neuron is not conducting any impulse i.e. when it is resting, the membrane i s more permeable to K⁺ and nearly impermeable to Na⁺.

Similarly, the membrane is impermeable to the negatively charged proteins. 

Thus the axoplasm acquires high concentration of K⁺ and negatively charged proteins and low concentration of Na⁺.

However the fluid outside the axon contains a low concentration of K⁺ and high concentration of Na⁺ . This forms a concentration gradient. These ionic gradients across the resting membrane are maintained by the active
transport of ions by the sodium-potassium pump which transports 3 Na⁺ outwards for 2 K⁺ into the cell. As a result, the outer surface of the
axonal membrane possesses a positive charge while its inner surface has a negative charge and is said to be polarised. This electrical potential across the resting membrane is called the Resting Potential.