 Dear students, in this module we shall discuss the resting membrane potential. Dear students, every non-excited or resting cell has a potential difference across its membrane. That is known as the resting membrane potential. The values of resting membrane potential vary in different types of cells. For example, the neurons which are not conducting any impulse have a typical minus 70 millivolt resting membrane potential. Now we shall have a view of the ions which are responsible to cause resting membrane potential. You know that plasma membrane is permeable to many species of ions. All these diffusible ions affect membrane potential across the membrane in proportion to their permeability. However, non-diffusible ions have no effect on resting membrane potential. The major ions which are involved in producing the resting membrane potential are the sodium, potassium and chloride ions. Now we shall discuss the equations which help to calculate the effect of a single ion or multiple ions. To calculate the effect of single ion on generating resting membrane potential, we use an equation that is called Nernst equation. While to calculate the effect of multiple ions on membrane potential, we use Gold's-Mann's equation. Both these equations apply equally to all excitable cells that is neurons and muscle cells. First we shall discuss the Nernst equation which is used to calculate the effect of single ion on the equilibrium potential of the membrane. According to Nernst equation, the equilibrium potential of a diffusible ion x depends on the nature log of the ratio of concentration of ion x on two sides of the membrane that is inside and outside the membrane. Apart from this, membrane potential gas constant R, absolute temperature i.e. T, valence of the ion z or fredic constant per B depends on it. So that we can read the Nernst equation as Ex i.e. equilibrium potential of diffusible ion x is equal to RT over Zf into log of concentration x inside the membrane over concentration of x outside the membrane. Now the Gold's-Mann equation is used to determine the effect of multiple ions on membrane potential. This equation is very similar to the Nernst equation. In this equation, we add the inside and outside concentrations of multiple ions and we get the equilibrium potential of multiple ions on the membrane. Dear students, now we shall discuss the role of ion channels in maintaining the resting membrane potential. Two types of ion channels i.e. the resting potassium selective channels and the voltage-gated sodium channels play major role in producing and maintaining the resting membrane potential. First we shall discuss the role of potassium selective channels. The potassium selective channels remain open in the resting membrane. They do not close. So the membrane is highly permeable to potassium ions. If the concentration of potassium ions changes on the outside of the cell, the cell membrane and its potential are highly sensitive. While the role of sodium channel is in this fact that they remain closed in the resting membrane. Due to this, the resting membrane remains relatively non-diffusable to sodium ions. If the concentration of sodium ions changes on the outside of the cell, then there is no effect on the membrane potential. Dear students, in addition to the effect of ions and ion channels, there is one other factor that has a major role in establishment of resting membrane potential and that phenomena is the active transport. Active transport moves ions against their concentration gradient. So it results in asymmetrical distribution of ions. The asymmetrical distribution of ions is the basis of resting membrane potential.