 Dear students, in this module we shall discuss the ionic basis of action potentials. The action potentials are produced by the movement of ions. The major ions that are involved in action potentials are the sodium and potassium ions. The factors that facilitate the movement of ions across the membrane include the unequal distribution of ions across the membrane. And the second factor is the presence of voltage-gated ion channels in the membrane. The production of an action potential depends firstly on the existence of an unequally distributed ionic potential across the membrane. This generates an electrochemical gradient that actually provides energy or potential energy for the movement of ions. Moreover, the second factor that is basic to generate action potentials is the presence of voltage-gated ion channels in the membrane of an excitable cell. These channels open or close in response to particular stimuli. The gating of ion channels forms the basis of all electrical signals in the nervous system. The opening or closing of the channels alters membrane permeability or membrane conductance to particular ions. This allows the flow of ionic currents through the channels which are driven by the electrochemical gradients which were established by unequal ionic distribution. The ionic currents alter membrane potential. Action in membrane potential is the basis of action potentials. As sodium and potassium ions are involved in generating action potentials, so we shall see that the sodium and potassium ions are moved through the sodium and potassium-gated channels. Now we shall see the role of these channels in producing action potentials. The sodium and potassium channels are quite different. These gated ion channels are quite different from the sodium-potassium pump that is involved in producing the resting membrane potential. Both these channels that is sodium-gated ion channel and potassium-gated ion channel are different from each other. They have different properties but their activities are interdependent and are responsible for nearly all the features of action potential.