Resting Membrane Potential: An Introduction

Resting Membrane Potential

• Definition and Basic Concept:

  • The resting membrane potential refers to the electrical potential difference across the plasma membrane of a cell when it is not actively transmitting electrical signals.
  • Fundamentally, at rest, the inside of the cell is slightly negative compared to the outside of the cell.
  • This difference in charge is crucial for the cell's ability to respond to stimuli and transmit information.

• Complexity and Underlying Mechanisms:

  • The establishment and maintenance of this negative charge inside the cell is a complex process involving several factors, hinting at the "other things involved" mentioned.
  • Key factors contributing to the resting membrane potential include:
    • Differential Distribution of Ions: There is an unequal distribution of ions across the cell membrane, particularly potassium ions (K^+), sodium ions (Na^+), and large negatively charged intracellular proteins.
    • Selective Permeability of the Membrane: The cell membrane exhibits selective permeability due to the presence of various ion channels. At rest, the membrane is much more permeable to K^+ ions than to Na^+ ions, primarily through "leak" channels.
      • Potassium Leak Channels: K^+ ions tend to diffuse out of the cell down their concentration gradient, leaving behind negatively charged molecules, thus contributing to the negative charge inside.
      • Sodium Leak Channels: While fewer, some Na^+ ions leak into the cell, partially counteracting the K^+ efflux.
    • Sodium-Potassium Pump (Na^+/K^+ ATPase): This active transport pump expels three Na^+ ions from the cell for every two K^+ ions it brings in. This is an electrogenic pump, meaning it contributes a small but significant direct negative charge to the inside of the cell (approximately -3mV) by pumping more positive charge out than in. Its primary role, however, is to maintain the concentration gradients for Na^+ and K^+ that drive the passive diffusion through leak channels.
    • Large Intracellular Anions: Proteins and other organic molecules inside the cell are often negatively charged and are too large to cross the cell membrane, contributing to the overall negativity inside.

• Typical Values:

  • The magnitude of the resting membrane potential varies depending on the cell type. For many neurons, it typically ranges from approximately -70mV to -90mV.