Resting membrane potential

• Nernst Equation: E(ion) = 2.303 (RT/zF) log (ion(o)/ion(i))
• The resting membrane potential can be calculated using the Goldman equation, a mathematical formula that takes into consideration the relative permeability of the membrane to different ions.
• Goldman equation

  
• The resting membrane potential is maintained by the sodium-potassium pump. This ion pump is a membrane-associated protein that transports ions across the membrane against their concentration gradients at the expense of metabolic energy.
• Eion is the membrane potential that would be achieved (at body temperature) if the membrane were selectively permeable to that ion.
• voltage-gated sodium ion channels

  • closed but capable of opening at resting potential (-70 mV)
  • open (activated) from threshold to peak potential (-50 - +30 mV)
  • closed and not capable of opening (inactivated) from peak to resting potential (+30 - -70 mV)
• voltage-gated potassium ion channels

  • closed at resting potential; delayed opening triggered at threshold; remains closed to peak potential (-70 mV - 30 mV)
  • open from peak potential through after hyperpolarisation (+30 - -80 mV)
• • electrical stimulus causes voltage-gated Na+ channels to open
  • membrane depolarises (more positive charge inside)
  • causes voltage-gated K+ channels to open and Na+ channels close
  • membrane repolarises to slightly below resting potential
  • K+ channels close