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Resting potential: Bernstein and Hodgkin-Katz theories
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- 1Topic Resting Potential The resting PotentialResting Potential- the electric potential differences between the interior and exterior of the cell when the cell is at physiological rest
- For different types of the resting potential differs from -50 m/V to -100 mV
The internal membrane surface surface carrier a negative charge relative to the external surface - 2The resting potential- Both electrodes outside
no potential difference
-Both electrodes inside
No potential difference
Prob inside, reference outside
negative resting potential - 3Nature of the Resting potential- Bernsteins Hypothesis- The cell membrane is permeable to potassium ion
- The resting potential is the equilibrium potential for the potassium ion
Calculated by Nernst Equation: - 4Grounds for Bernsteins Hypothesis- The concentration inside the cell is higher than outside the cell
Concentration gardient move the K+ out of the cell
-The inside of the cell has negative electric potential
the electric field move K+ into the cell
Equilibrium is possible - 5Equilibrium ConditionsThe resting membrane is permeable to potasium ions only or- ,
All others ions are also in equilibrium- The electric and concentration gardients balance the fluxes into out of the cell - 6Discrepancy between Bernsteins Hypothesis and ExperimentThe potassium hypothesis is incomplete-
The membrane is permeable to other ions as well - 7Non- Equilibrum distribution of sodium IonsThe cell membrane at rest is slightly permeable to sodium ions
- The sodium ions is are not in equilibrium- both electric and concentration gardients move the ions into the cell - 8The Hodgkin- Katz TheoryThe resting potential is the potential of a steady state, not of an equilibrium state
The resting potential is the net result of the fluxes of potassium, sodium and chloride ions across a membrane - 9Charge flux across a membrane- The charge flux across the membrane is due to the monovalent potassium, sodium and chloride ions.
The total charge flux density is the sum of the flux densities of the cations minus the sum of the flux densities: J=Jk+Jna-Jcl= 0 - 10The steady flux- The ion flux changes the membrane potential
-The growing membrane potential slow down the diffusion of the ions - 11The condition for a steady stateThe chloride ions distribution at rest is close to equilibrium: Jcl=0
- 12Membrane Permeability-Some potassium channels in the resting membrane are open- the permeability to potassium ion is relatively large
- The sodium channels in the resting membrane are closed- the permeability to sodium ions is very small - 13Driving forcesThe concentration and electric potential gardients moves potasium ions in opposite direction- the net driving force for potassium ion is small
- The concentration and electric potential gardients move the sodium ions in the same direction- the net driving force is large - 14The K+ and Na+ fluxes and steady stateIt is possible for the potassium and sodium fluxes to be equal opposite to each other- a steady state can be established
- 15The goldman equation for the steady state resting potential- (chloride ion)The intracellular and extracellular concentrations of the chloride ion are reversed relative to the concentrations of potassium and sodium ions because chloride ion is negative
- 16The goldman equation- ValidityCorrectly describes the resting potential of cell when the concentration of K+ is high
- Resting potential of almost all cell membranes can be correctly calculated with goldman equation - 17The resting potential analysisThe resting membrane potential is determined by the steady state ion concentration differences between the intracellular and extracellular fluid
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- Fichas sobre Sin título, creado por engjeeell el 14/06/2015.
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- engjeeell · jun 2015
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- 19 feb 2016
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