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34 Cards in this Set
- Front
- Back
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Why do we care about electrophysiology?
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Because ALL local and propagated electrical signals generated by a cell are driven by changes in the resting Em.
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Why is electrophysiology essential?
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It is necessary for maintaining cell, tissue, and organism homeostasis.
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What is "DIFFUSION POTENTIAL"?
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The ability of an ion to travel through a semipermeable membrane
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What 2 factors regulate the magnitude w/ which each permeable ion contributes to the resting membrane diffusion potential?
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1. Transmembrane concentration difference of ea permeable ion
2. Mobility of permeable ion WITHIN the membrane relative to ions of opposite charge. |
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What is MOBILITY of an ion?
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The velocity of ion movement
----------------------------- Unit of Driving Force |
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What does difference in cation vs anion mobility have to do with Membrane Potential?
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Leads to a:
-SEPARATION of charge -Attractive force betwn ions -ELECTRICAL POTENTIAL DIFFERENCE between the ions |
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What are the 2 determinants of ion intramembrane MOBILITY?
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1. Diameter/shape of each ion and the pore thru which it goes
2. Ionic/Vanderwaals forces btwn ions and AA's in proteins facing the inner channel pore |
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Dipole
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An equal pos and neg charge separated by a finite difference
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What is Diffusion Potential a result of?
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Dipoles crossing the membrane in a nonrandom order due to force of a chemical gradient.
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Is the dffusion potential caused by a difference in charge between two components?
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NO - the intra/extracellular compartments are electroneutral actually; the separation of charge is ONLY IN THE MEMBRANE.
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What is the 'state' nature of the Diffusion Potential?
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STEADY STATE - requires a constant input of energy to maintain the chemical gradient.
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What is the equation for simple diffusion potential?
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Pcat-Pan 2.3RT [IP]o
Ediff = -------- x ----- x ---- Pcat+Pan nF [IP]i |
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Units of Ediff
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millivolts mV
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What is the permeability of each ion proportional to?
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Its intramembrane diffusion coefficient (D)
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What is the Diffusion Coefficient (D) proportional to?
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The intramembrane mobility of an ion (beta)
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What else is permeability of an ion proportional to?
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the number of open channels in the membrane for each particular ion.
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What does 2.3RT/nF = ?
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60 mV (at 37 ' C)
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When is the Nernst potential equation used instead of the simple diffusion potential equation?
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When one of the members of a cation/anion pair is IMPERMEABLE to the membrane.
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How is the nernst equationd different from that for simple diffusion potential?
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It is only for one ion (the cation), and so permeability is not a factor.
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What does the diffusion potential become when one member of a cation/ion pair is impermeable?
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Becomes the equilibrium potential for the permeable ion.
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What is an Equilibrium Potential?
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The condition where a CHEMICAL driving force is BALANCED by an EQUAL/OPPOSITE ELECTRICAL force.
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What is the equilibrium potential for potassium in a mammalian nerve or muscle fiber?
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-89 mV
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What is the normal K concentration inside/outside a mammalian nerve/muscle cell?
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Inside = 140 mM
Outside = 4.7 mM |
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What happens to individual chemical/electrical potential differences when equilibrium potential is reached?
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The remain CONSTANT and DO NOT CHANGE.
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Is energy required to maintain the equilibrium potential for an ion?
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NO
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How much change in intracellular K would have to occur to set up an Ek of -88 mV (instead of -89 mV)?
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For a squid axon membrane:
0.00001% - too small to detect. |
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What is the normal concentration of Ca2+ inside/outside a mammalian nerve or muscle fiber?
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Ca inside = 10^-7 M
Ca outside = 1.6 x 10^-3 M |
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Based on the concentration gradient where does Ca want to go?
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INTO the cell - there is much more outside than inside.
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How neg/pos would a cell have to be to balance the concentration gradient and prevent Ca influx?
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VERY positive (to prevent the positive charge from rushing in)
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What would the Eca be if the membrane were to become permeable to it?
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126.7 mV
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What equation is used for calculating the total resting membrane potential?
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GHK - goldman hodgkin katz
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What ions are included in the GHK equation for a squid axon?
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Na, K, Cl
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For a squid axon the measured resting Em is:
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-65 mV
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What is the effect of extracellular K on the resting Em in a squid axon?
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Increasing K outside will make the cell Em be closer to the Ek (hyperpolarize).
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