Resting Membrane Potential PDF

Resting membrane potential Students will be able to describe how the resting membrane potential is generated and sustained in excitable cells, emphasizing the roles of diffusion potentials, ion concentration gradients, and the Na⁺/K⁺ ATPase pump. The resting membrane potential is the voltage diffe...

Resting membrane potential Students will be able to describe how the resting membrane potential is generated and sustained in excitable cells, emphasizing the roles of diffusion potentials, ion concentration gradients, and the Na⁺/K⁺ ATPase pump. The resting membrane potential is the voltage difference across the membrane of excitable cells, such as nerve and muscle cells, during periods of inactivity (i.e., at rest). By convention, the intracellular potential is compared to the extracellular potential when expressing the membrane potential. The resting membrane potential is primarily established by diffusion potentials, which arise due to ion concentration differences across the cell membrane. These concentration gradients are maintained by active transport mechanisms. Each permeable ion strives to move the membrane potential toward its own equilibrium potential. Ions with greater permeability or conductance at rest contribute more significantly to the resting potential, while ions with lower permeability have minimal or no effect. In most excitable cells, the resting membrane potential typically ranges from –70 mV to –80 mV. This value is largely explained by the relative permeability of the cell membrane to different ions. The resting potential is close to the equilibrium potentials of K⁺ and Cl⁻, as these ions have high permeability at rest. In contrast, the potential is far from the equilibrium potentials of Na⁺ and Ca²⁺, given their low permeability. Students will be able to analyze the contributions of key ions (K⁺, Na⁺, Cl⁻, and Ca²⁺) to the resting membrane potential by applying the chord conductance equation and understanding the impact of ion permeability and conductance on membrane potential. A method for evaluating the contribution of each ion to the membrane potential is through the chord conductance equation. This equation factors in the equilibrium potential for each ion (determined by the Nernst equation) and weights it by the ion's relative conductance. Ions with higher conductance have a significant influence, driving the membrane potential closer to their equilibrium potentials. In contrast, ions with lower conductance exert minimal impact on the membrane potential. An alternative method to address this involves the Goldman equation, which evaluates each ion's contribution based on its relative permeability instead of conductance. The chord conductance At rest, the membranes of excitable cells are far more permeable to K⁺ and Cl⁻ than to Na⁺ and Ca²⁺. These differences in permeability account for the resting membrane potential. What role, if any, does the Na⁺-K⁺ ATPase play in creating the resting membrane potential? The answer has two parts. First, there is a small direct electrogenic contribution of the Na⁺-K⁺ ATPase, which is based on the stoichiometry of three Na⁺ ions pumped out of the cell for every two K⁺ ions pumped into the cell. Second, the more important indirect contribution is in maintaining the concentration gradient for K⁺ across the cell membrane, which then is responsible for the K⁺ diffusion potential that drives the membrane potential toward the K⁺ equilibrium potential. Thus, the Na⁺-K⁺ ATPase is necessary to create and maintain the K⁺ concentration gradient, which establishes the resting membrane potential. (A similar argument can be made for the role of the Na⁺-K⁺ ATPase in the upstroke of the action potential, where it maintains the ionic gradient for Na⁺ across the cell membrane.)