Y1S1 008 III Physiology: Resting Membrane Potential

Resting Membrane Potential (RMP) and Nerve Physiology

• The resting membrane potential (RMP) is the electrical potential difference across the cell membrane in excitable tissues, such as nerve cells, cardiac cells, and skeletal muscle cells.
• The RMP of nerve cells is around -70mV, while that of cardiac and skeletal muscle cells is between -85mV to -90mV.

Genesis of the Resting Membrane Potential

• The RMP is due to the uneven distribution of electrolytes (Na+, K+, Cl-) inside and outside the cell membrane.
• An excess of nondiffusible protein ions and other anions inside the cell makes the inside of the nerve membrane more negative than the outside.

Role of Protein Channels and Carriers

• Two transport proteins are primarily responsible for the genesis of the RMP:
  • K+ leaky channels
  • Na+/K+ ATPase pump (an electrogenic pump that extrudes 3Na+ for every 2K+ ions, contributing a few mV to the RMP)

Development of the Resting Membrane Potential

• The RMP is developed largely due to diffusion forces, including concentration and electrical gradients for most ions across the cell membrane.
• The equilibrium potential, where the influx and efflux of Cl- are equal, is around -70mV.

Nernst Equation

• The Nernst equation is used to calculate the equilibrium potential (Em) of an ion:
  • Em = RT/F * ln([X]0 / [X]i)
  • Where R is the universal gas constant, T is the absolute temperature, F is the Faraday constant, Z is the valency of the ion, and [X]0 and [X]i are the concentrations of the ion outside and inside the cell, respectively.

Examples of Nernst Equation Calculations

• ECl- = -61 log (125/9) = -70mV
• ENa+ = +61 log (140/14) = +61 mV
• EK+ = +61 log (4/140) = -94.1 mV