1. ECF and ICF show no electrical potential (0 mV)

3. An electrical potential exists across the membrane.

4. All cells are polarized. The value of the potential varies from cell to cell but they are all polarized. Negative inside, positive outside. The sign of the potential is referred by convention to that of the inside.

6. Why are cells polarized?

9. What determines the value of the electrical potential? Concentration gradients of ions. Permeability characteristics of the membrane.

11. Electrical potential: potential difference or potential. Units: Volt, in biology mV. Separated charges (+) and (-) have the potential for work if they come together. Current: movement of charges. Unit Ampere. Resistance: hindrance to movement of charges. Unit: Ohm

12. Equilibrium Potential Equilibrium potential: Electrical potential (mV) that balances the concentration (chemical) gradient. Nernst Equation.

13. Nernst Equation Given a chemical gradient of ion X, the equilibrium potential Ex, can be calculated as –Ex = (RT/Fz) ln [X]out / [X]in –z is the charge of the ion. –R and F are constants. –T is temperature in K.

14. Nernst Equation Simplified E x in millivolts = + or – 60 log [X inside ]/[X outside ] This works for univalent ions such as Na+ or K+ This applies the constants (R,F) and works at normal body temperature (K) The sign will be + for negative ions and – for positive ions The answer is for the potential INSIDE the membrane

15. K potentials Resting membrane potential (V m ) = -90mV. K + chemical gradient pulling V m to –101 mV. The resting membrane is more permeable to K + and the V m is closer to E K.

16. Membrane Permeability Two main factors determine V m –Chemical gradient. –Membrane permeablity

17. Membrane Permeability and Concentrations –Goldman-Hodgkin-Katz equation

19. Anion and Cation distribution [K+] 155 mEq/l [K+] 4mEq/l [Na+] 12 mEq/l [Na+] 145 mEq/l Fixed Anions

20. Resting Membrane Potential

21. Na-K-Pump Keeps Gradients.