NEURONAL MEMBRANE POTENTIAL AND SODIUM CHANNELS
Illustrations of ion flow contributing to the neuronal resting potential and three states of the sodium channel in neuronal excitability.
A. The movement of ions across the cell membrane is dependent upon both concentration and electrostatic forces. Ions flow from high concentrations to lower concentrations as depicted by the flow of K+ ions from inside the cell, where the concentration is high, to outside the cell, where the concentrations is lower.
B. Ions are attracted to charges of the opposite polarity. In this example, K+ ions flow from the extracellular environment, which is positive in relationship to the intracellular space, which is negative. Both concentration and electrostatic forces determine flow of ions. The potential at which a through the membrane in either direction.
Three states of the sodium channel. C. In the resting state, no ion flow occurs due to closure of the activation gate. D. When the membrane begins to depolarize, the activation channel opens and ion flow occurs. E. As the cell becomes depolarized, the inactivation gate closes and no further ion flow occurs. Only when the cell repolarizes does the sodium channel return to the resting state.