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Resting membrane potential

Resting membrane potential. 1 mV= 0.001 V membrane separates intra- and extracellular compartments inside negative (-80 to -60 mV) due to the asymmetrical distribution of ions across the cell membrane AND the differential permeability of the membrane to these ions.

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Resting membrane potential

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  1. Resting membrane potential • 1 mV= 0.001 V • membrane separates intra- and extracellular compartments • inside negative (-80 to -60 mV) • due to the asymmetrical distribution of ions • across the cell membrane • AND the differential permeability of the membrane to these ions

  2. Channels allow ions to diffuse across membranes Voltage-gated: Na+ channels, K+ channels, Ca2+ channels Ligand-gated: neurotransmitters (acetylcholine, glutamate)

  3. Potassium Equilibrium Potential Figure 5-34a

  4. Figure 5-34b

  5. Resting membrane potential is due mostly to high potassium permeability Figure 5-34c

  6. The Nernst equation describes an ion’s equilibrium potential • where: • R is the gas constant (8.314 X 107 dyne-cm/mole degree), • T is the absolute temperature in o Kelvin, • z is the charge on the ion • F is the Faraday (the amount of electricity required to chemically alter one gram equivalent weight of reacting material = 96,500 coulombs).

  7. A simpler version of the Nernst equation At 37ºC: When ions can move across a membrane, they will bring the membrane potential to their equilibrium potential.

  8. Typical ion concentrations

  9. Calculating the membrane potential for a cell that is only permeable to K+ [K+]out = 5 mM [K+]in = 150 mM Ek = 61 x (-1.5) = -92 mV

  10. Sodium Equilibrium Potential ENa = 61 x 1 = +61 mV

  11. The Na+-K+-ATPase (“sodium pump”) works to keep intracellular K+ high and Na+ low

  12. Predicting the membrane potential (Vm) • The membrane potential can be described by the relationship between ion permeabilities and their concentrations • The Goldman equation: • Vm = PNa[Na+]out+ PK[K+]out+ PCl[Cl-]in 61 log PNa[Na+]in+ PK[K+]in+ PCl[Cl-]out • At the resting potential • a. K+ is very close to equilibrium. • b. Na+ is very far from its equilibrium. • c. PK >> PNa

  13. Real neurons and “Dynamic Polarization” Purkinje cell Cerebellum Pyramidal cell Layer V neocortex Input Dendrites Dendrites Axon collaterals Collateral branch Axon Output Axon Santiago Ramon y Cajal, 1900

  14. Electrical Signals: Ion Movement • Resting membrane potential determined by • K+ concentration gradient • Cell’s resting permeability to K+, Na+, and Cl– • Gated channels control ion permeability • Mechanically gated • Ligand gated • Voltage gated

  15. Current flow through ion channels leads to changes in membrane potential Ohm’s Law: V = I * R V = voltage, I = current (Amps), R = resistance (Ohms) I = V/R or I = V * G G = conductance (Siemens) For current to flow, there must be a driving force (Vm - Eion) > or < 0, thus I = (Vm - Eion) * G If current flows across a resistance--the cell membrane acts like one--there is a change in voltage (membrane potential).

  16. Graded Potentials Graded potentials can be: EXCITATORY or INHIBITORY (action potential (action potential is more likely) is less likely) The size of a graded potential is proportional to the size of the stimulus. Graded potentials decay as they move over distance.

  17. Graded potentials decay as they move over distance.

  18. Cable theory

  19. Action Potential 1 ms • All-or-none • Not due to “membrane breakdown” +40 “Overshoot” 0 mV Shock -80

  20. Na+-dependence of AP

  21. Voltage-clamp

  22. Voltage-clamp of squid giant axon

  23. Isolation of Na and K currents

  24. I/V relationship of Na and K channels

  25. HH model

  26. Electrical Signals: Action Potentials Figure 8-9 (1 of 9)

  27. Electrical Signals: Action Potentials Figure 8-9 (2 of 9)

  28. Electrical Signals: Action Potentials Figure 8-9 (3 of 9)

  29. Electrical Signals: Action Potentials Figure 8-9 (4 of 9)

  30. Electrical Signals: Action Potentials Figure 8-9 (5 of 9)

  31. Electrical Signals: Action Potentials Figure 8-9 (6 of 9)

  32. Electrical Signals: Action Potentials Figure 8-9 (7 of 9)

  33. Electrical Signals: Action Potentials Figure 8-9 (8 of 9)

  34. Electrical Signals: Action Potentials Why is AP peak < ENa? Figure 8-9 (9 of 9)

  35. Electrical Signals: Voltage-Gated Na+ Channels Na+ channels have two gates: activation and inactivation gates Figure 8-10a

  36. Electrical Signals: Voltage-Gated Na+ Channels Figure 8-10c

  37. Electrical Signals: Voltage-Gated Na+ Channels Figure 8-10d

  38. Electrical Signals: Refractory Period

  39. How does an AP travel down an axon? Figure 8-14

  40. AP propagation

  41. Figure 8-15, step 5

  42. Speed of AP conduction is governed by: • Diameter of the axon • Resistance of the axon membrane to ion leakage

  43. Myelin sheath “insulates” axons

  44. Saltatory conduction

  45. Axon size matters 1 mm

  46. Myelination increases conduction velocity Top speed=225 mph Top speed=170 mph Kawasaki Z750S

  47. Electrical Signals: Graded Potentials Subthreshold and suprathreshold graded potentials

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