1. Neural Signaling: The Membrane Potential Lesson 9

2. Membrane Structure n Barrier l Compartmentalization n Semipermeable l selectively leaky n Fluid Mosaic Model l Phospholipids l Proteins ~

3. Phospholipid Bilayer Hydrophilic heads  (phosphate) Hydrophobic tails  (lipid)

4. Membrane Proteins n Channels n Pumps l active transport n Receptor protein sites l bind messenger molecules n Transducer proteins: l 2d messenger systems n Structural proteins l form junctions with other neurons ~

5. Membrane Proteins: Ionophores n Ion Channels n Non-gated l always open n Gated l chemically-gated l electrically-gated l mechanically-gated ~

6. Chemically-Gated Channels n ligand-gated n Ionotropic l receptor protein = channel l direct control ---> fast n Metabotropic l second messenger system l indirect ---> slow ~

7. Membrane Proteins OUTSIDE INSIDE

8. Metabolic pumps: Active Transport n Membrane proteins n Pump ions l require energy l Na+ - K+ l Ca++ (calcium) n Also various molecules l nutrients l neurotransmitters ~

9. Biolelectric Potential n Communication within neuron l electrical signal n electric current = movement of electrons n Bioelectric: movement of ions ~

10. Ion Distribution n Particles / molecules l electrically charged n Anions l negatively charged n Cations l positively charged ~

11. n Anions (-) l Large intracellular proteins l Chloride ions Cl- n Cations (+) l Sodium Na+ l Potassium K+ ~ Ion Distribution

12. Resting Membrane Potential Membrane outside inside Na + Cl - K+K+ K+K+ A-A- +++++++++++ ----------- +++++++++++ -----------

13. n more negative particles in than out n Bioelectric Potential l like a battery l Potential for ion movement current ~ Membrane is polarized

14. INSIDE POS NEG Bioelectric Potential OUTSIDE

15. Forces That Move Ions n Concentration (C) l particles in fluid move from area of high to area of low concentration l diffusion, random movement n Electrostatic (E) l ions = charged particles l like charges repel l opposite charges attract ~

16. Equilibrium Potential n Also called reversal potential n Distribution of single ion across membrane l e.g., E K+, E Na+, E Cl- n Potential for movement of ion if channel opens l units millivolts (mV) l Potential outside = 0, by convention ~

17. Equilibrium Potential n R = gas constant n F = Faraday constant n T = temperature (K) n Z = valence (charge) of ion ~

18. Equilibrium Potential K + : z = +1 Cl - : z = -1 Mg ++ : z = +2

19. Equilibrium Potential n Constants never change n Assume 25 o C (298 o K) n Use log 10 ~

20. Equilibrium Potential

21. Membrane Potential n Net bioelectric potential l for all ions l units = millivolts (mV) n Balance of both gradients l concentration & electrostatic n V m = -65 mV l given by Goldman equation ~

22. Membrane Potential: Goldman Equation n P = permeability l at rest: P K : P Na : P Cl = 1.0 : 0.04 : 0.45 n Net potential movement for all ions n known V m :Can predict direction of movement of any ion ~

23. C Organic anions - Membrane impermeable Opposing electrical force not required A-A- V m = -65 mV

24. Chloride ion C E Cl - V m = -65 mV n Concentration gradient equal to electrostatic gradient. n Leaks out neuron n E Cl- = - 65 mV ~

25. K + C E V m = -65 mV Potassium ion n Concentration gradient greater than electrostatic gradient. n Leaks out neuron n E K = - 75 mV ~

26. Sodium ion Na + CE V m = -65 mV n Concentration gradient and electrostatic gradient into neuron. n E Na+ = +55 mV ~

27. Metabolic Pumps n Active Transport mechanisms l Require energy n Move materials against gradient l Na+ - K+ l Calcium - Ca++ l Nutrients, etc.~

28. Na+ - K+ Pump n Moves ions against gradients l Pumps 3 Na+ out of cell l 2 K+ into cell n Maintains gradients at rest l no active role in signalling l Energy = ATP ~

29. Inside Outside Na+ K+ Na+ ATP

30. Inside Outside Na+ K+