1. Neural Signaling: The Membrane Potential Lesson 8

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

3. Phospholipid Bilayer n Hydrophilic heads  n (phosphate) n Hydrophobic tails  n (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 OUTSIDE INSIDE

6. 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 ~

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

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

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

10. Bioelectric Potential OUTSIDE INSIDE POS NEG

11. 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 ~

12. Concentration gradient HI Lo

13. HI Lo Concentration gradient

14. HI Lo Concentration gradient

15. Equilibrium

16. Na+K+ like charges repel Electrostatic gradient

17. Na+ A- opposite Electrostatic gradient charges attract

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

19. Membrane Potential n Net bioelectric potential l for all ions l units = millivolts (mV) n Balance of both gradients l concentration & electrostatic n E m = -70 mV l given by Goldman equation ~

20. C Organic anions - Membrane impermeable Opposing electrical force not required A-A- E m = -70 mV

21. Chloride ion n E Cl - = - 70 mV n Concentration gradient equal to electrostatic gradient. n No net movement at resting potential ~ C E Cl - E m = -70 mV

22. K + C E E m = - 70 mV Potassium ion n E K = - 90 mV n Concentration gradient greater than electrostatic gradient. n Leaks out neuron ~

23. Sodium ion E m = - 70 mV n E Na+ = +50 mV n Concentration gradient and electrostatic gradient into neuron. ~ Na + CE

24. 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 roll in signalling l Energy = ATP ~