Membrane Potentials

Membrane Potentials

1. Ionic Gradients Generate Membrane Potential

   • Membrane is impermeable to ions
     • Ion Channels- Ions move with concentration gradient
     • Ion transporters- Move ions against concentration gradient
       • Na+/K+ Pump- Moves 3 Na+ out/2 K+ in
         • Results in HIGH K+ and LOW Na+ INSIDE
       • Uses ATP to provide energy for process

2. Equilibrium Potentials

   • Ions attract opposites and repel like
     • Equilibrium potential- The charge needed to prevent ions from diffusing down concentration gradient
       • Difference in concentrations of ions across membrane
         • Large difference = large charge
   • Example: A cell which is fully permeable to K+/Na+, and +/- charges are balanced(resting potential = 0)
     • Concentration gradient will affect ion movement
       • If there is more K+ in the cell, K+ will leave, making the cell more negative because negatives are no longer balanced out by positives
   • Keq(K+): -88 mV
     • More Negative inside will cause K+ to flow inwards
   • Why Is the Neuron Negatively charged?
     • Na+/K+ pump is electrogenic- -1 charge generated
     • Proteins are negatively charged
     • Major factor: Membrane is more leaky for K+ ions than Na+. Leads to a net loss of charge
   • Equilibrium potential is dependent on several ions
     • Na+, K+, Cl- all contribute to membrane potential
     • Membrane Potential: -70 mV due to greater permeability for K+
     • Cl- is not actively transported into the cell, and Cl- equilibrium potential is near resting potential so there is little driving force
   • Normal Keq(Na+) : +60 mV

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