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Neurophysiology

Neurophysiology. The Resting Membrane Potential. V m -70 mV. V. V. Intracellular. Extracellular. V m =V in -V out. Three Concepts. 1. Concentration Gradients. 2. Electrical gradients. Selective permeability of the membrane. Solid barrier in place. 100 NaCl. 0 NaCl.

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Neurophysiology

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  1. Neurophysiology

  2. The Resting Membrane Potential

  3. Vm -70 mV V V Intracellular Extracellular Vm=Vin-Vout

  4. Three Concepts 1. Concentration Gradients 2. Electrical gradients • Selective permeability • of the membrane

  5. Solid barrier in place 100 NaCl 0 NaCl Outside Inside

  6. Solid barrier in place 0 100 Na+ 100 Cl- 0 Na+ 0 Cl- 0 0 Outside Inside

  7. Barrier removed 100 Na+ 100 Cl- 0 Na+ 0 Cl- 0 0 Outside Inside Na+ Concentration gradient= 100 Cl- Concentration gradient= 100

  8. Barrier removed 50 Na+ 50 Cl- 50 Na+ 50 Cl- 0 0 Outside Inside Na+ Concentration gradient= 0 Cl- Concentration gradient= 0

  9. Measure voltage difference System at equilibrium 0 50 Na+ 50 Cl- 50 Na+ 50 Cl- 0 0 Outside Inside Na+ Concentration gradient= 0 Cl- Concentration gradient= 0

  10. Solid barrier in place 0 100 Na+ 100 Cl- 0 Na+ 0 Cl- 0 0 Outside Inside

  11. Replace with Na+ permeable membrane 0 100 Na+ 100 Cl- 0 Na+ 0 Cl- 0 0 Outside Inside Na+ Concentration gradient= 100

  12. Replace with Na+ permeable membrane +100 50 Na+ 100 Cl- 50 Na+ 0 Cl- -50 +50 Outside Inside Na+ Concentration gradient= 0

  13. Replace with Na+ permeable membrane +100 50 Na+ 100 Cl- 50 Na+ 0 Cl- -50 +50 Outside Inside Na+ Concentration gradient= 0

  14. Replace with Na+ permeable membrane System at equilibrium +50 75 Na+ 100 Cl- 25 Na+ 0 Cl- -25 +25 Outside Inside Na+ Concentration gradient= 50

  15. Replace with Cl- permeable membrane +50 75 Na+ 100 Cl- 25 Na+ 0 Cl- -25 +25 Outside Inside Cl- Concentration gradient= 100

  16. Replace with Cl- permeable membrane -50 75 Na+ 50 Cl- 25 Na+ 50 Cl- +25 -25 Outside Inside Cl- Concentration gradient= 0

  17. Replace with Cl- permeable membrane System at equilibrium -25 75 Na+ 62.5Cl- 25 Na+ 37.5 Cl- +12.5 -12.5 Outside Inside Cl- Concentration gradient= 25

  18. Ion Concentrations in Neurons c e c e c e (Giant Squid Axon) Ion [X]I [X]O Na+ 50mM 440mM Cl- 52mM 560mM K+ 400mM 20mM

  19. Nernst Equation Ex = RT/zF * ln ([X]o/[X]i) where R =universal gas constant (8.31 joules/mole-oK) T = temperature (oK) z = charge of the ion F = faraday constant (96,500 coulombs/mole) If z = 1 and T = 293o K, then Ex = 58 log ([X]o/[X]i) If z = -1 and T = 293o K, then Ex = -58 log ([X]o/[X]i) If z = 2 and T = 293o K, then Ex = 29 log ([X]o/[X]i)

  20. Ion Concentrations in Neurons c e c e c e (Giant Squid Axon) Ion [X]I [X]O Na+ 50mM 440mM Cl- 52mM 560mM K+ 400mM 20mM ENa+ = +55mV ECl - = -60mV EK+ = -75mV

  21. Goldman Equation or Goldman-Katz Equation Takes into account all ions at the same time and the different permeabilities of the membrane to those ions. At rest: PK+ = 1.00 PNa+= .04 PCl- = .45

  22. (PNa+[Na+]o + PK+[K+]o + PCl-[Cl-]i) Erm = 58 log (PNa+[Na+]i + PK+[K+]i + PCl-[Cl-]o) (.04(440) + 1.0 (20) + .45 (52)) = 58 log (.04 (50) + 1.0(400) + .45(560)) (17.6 + 20 +23.4) = 58 log (2.0 + 400 + 252) 61.0 = 58 log 654.0 = 58 log (.093) = 58 (-1.03) = -59.8mV

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