Lecture Notes: Resting Membrane Potential and Ion Distribution in Neurons

Ion Distribution and Resting Membrane Potential

• Ion Distribution Across Membrane:

  • Inside of neuron: More negatively charged compared to outside.
  • Outside ions: Sodium (Na+), Chloride (Cl-), Calcium (Ca2+).
  • Inside ions: Potassium (K+).
  • This distribution results in a negative membrane potential.

• Role of Ion Distribution:

  • Generates resting membrane potential.

Ion Permeability and Membrane Potential

• Non-gated (Leak) Channels:

  • Some are open at rest.
  • More potassium (K+) channels open than sodium (Na+) channels.
  • Membrane more permeable to K+.

• Potassium Movement:

  • K+ flows out due to electrochemical gradient.
  • Aims to reach K+ equilibrium potential (~ -80 mV).

• Equilibrium Potential:

  • If only K+ channels were open, the potential would reach K+'s equilibrium potential.
  • Other non-gated channels (Na+, Cl-):
    • Cl- permeability: About half of K+.
    • Na+ permeability: 25-40 times less than K+.

• Resting Membrane Potential:

  • Slightly more positive than K+ equilibrium potential due to Na+ and Cl- movement.

Maintenance of Ionic Gradients

• Sodium-Potassium Pump (Na+/K+ pump):
  • Key in maintaining concentration and electrical gradients.
  • Uses ATP to transport ions:
    • Moves 3 Na+ out, 2 K+ in.
    • ATP to ADP conversion causes conformational change.
    • Maintains electrochemical gradients.

Calculating Membrane Potential

• Nernst Equation:

  • Calculates one ion's equilibrium potential.
  • Predicts ion movement direction.

• Goldman Equation:

  • Used for calculating membrane potential considering permeability to K+, Na+, Cl-.
  • Involves constant (61) from gas constant and temperature.
  • Permeability values:
    • K+: 1
    • Na+: 0.04
    • Cl-: 0.4
  • Concentration Considerations:
    • For Cl-, inside/outside concentration reversed in formula.

• Calculated Resting Membrane Potential: ~ -65 mV.