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Neural Signaling: The Membrane Potential

Neural Signaling: The Membrane Potential. Lesson 9. Membrane Structure. Barrier Compartmentalization Semipermeable selectively leaky Fluid Mosaic Model Phospholipids Proteins ~. Phospholipid Bilayer. Hydrophilic heads  (phosphate) Hydrophobic tails  (lipid). Membrane Proteins.

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Neural Signaling: The Membrane Potential

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  1. Neural Signaling:The Membrane Potential Lesson 9

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

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

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

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

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

  7. Membrane Proteins OUTSIDE INSIDE

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

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

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

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

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

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

  14. Bioelectric Potential POS NEG OUTSIDE INSIDE

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

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

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

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

  19. Equilibrium Potential • Constants never change • Assume 25 oC (298 oK) • Use log10 ~

  20. Equilibrium Potential

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

  22. Membrane Potential: Goldman Equation • P = permeability • at rest: PK: PNa: PCl = 1.0 : 0.04 : 0.45 • Net potential movement for all ions • known Vm:Can predict direction of movement of any ion ~

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

  24. Chloride ion Cl- C • Concentration gradient equal to electrostatic gradient. • Leaks out neuron • ECl- = - 65 mV ~ Vm = -65 mV E

  25. Potassium ion E • Concentration gradient greater than electrostatic gradient. • Leaks out neuron • EK = - 75 mV ~ Vm = -65 mV K+ C

  26. Na+ Sodium ion C E • Concentration gradientandelectrostatic gradient into neuron. • ENa+ = +55 mV ~ Vm = -65 mV

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

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

  29. Na+ Na+ Na+ K+ K+ Inside Outside Na+ Na+ Na+ K+ K+ ATP

  30. Na+ Na+ Na+ Inside Outside K+ K+ K+ K+

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