Membrane Potential and Ion Concentration

Key Concepts

• Potassium Concentration
  • Higher concentration inside the cell: ~150 mmol/L
  • Lower concentration outside the cell: ~5 mmol/L
• Concentration Gradient
  • Drives potassium (K) out of the cell.
  • Leaves anions inside, creating a negative charge.
• Negative Charge Attraction
  • Negative charge inside the cell attracts potassium back.
  • Occurs until equilibrium is reached.

Equilibrium Potential

• Membrane Potential (Vm)
  • Equilibrium occurs at -92 mV.
  • Balances out the concentration gradient of potassium.

Thought Experiment

• Injecting Positive Charge
  • Introducing positive charge into the cell makes the membrane potential less negative.
  • Example: Changing from -92 mV to -46 mV.
  • Potassium finds less attraction and leaves the cell.
• Returning to Equilibrium
  • More potassium leaving increases anion concentration inside.
  • Membrane potential returns to -92 mV.

Importance of Concentration Gradient and Permeability

• Concentration Gradient
  • Potassium's desire to leave the cell.
• Permeability
  • Means for potassium to leave the cell.
• Without both, no membrane potential is created.

Membrane Potential Formula

• Formula for Vm
  • Vm = 61.5 * log([K outside] / [K inside])
  • Potassium (K) example: -92 mV.

Membrane Potentials for Other Ions

• Sodium (Na)
  • Positive 67 mV
• Chloride (Cl)
  • Negative 86 mV
• Calcium (Ca)
  • Positive 123 mV
  • Note: Calcium has 2+ charge, changing constant to 30.75 in formula.

Ion Movements

• Potassium (K)
  • Positive ion moving out of the cell.
• Sodium (Na)
  • Positive ion moving into the cell.
• Chloride (Cl)
  • Negative ion moving into the cell.
• Calcium (Ca)
  • Positive ion moving into the cell.