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35 Cards in this Set
- Front
- Back
Define resting potential. What is its range?
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Charge of inside of cell relative to charge of outside of cell, e.g., if Vrest = -70 mV, inside of cell is 70 mV more negative than outside.
Range is -40 to -90 mV |
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What occurs during depolarization?
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Inside of cell becomes more positive
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What occurs during hyperpolarization?
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Inside of cell becomes more negative
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What does current describe?
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The direction of flow of POSITIVE charges
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What is Ohm's law?
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V = IR
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What is inward current? Outward current?
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Inward current: flow of POSITIVE charges into a cell
Outward current: flow of POSITIVE charges out of a cell |
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How does intracellular charge compare to extracellular charge?
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The cell is more negative on the inside
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What are the effect of concentration and electrochemical gradients on sodium and potassium?
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Sodium wants to enter cell because cell interior is more negative, and because there is a lower [Na] within the cell.
There is a net leakage of K out of the cell, this is due to a concentration gradient pushing K+ outward (there is a lower [K+] outside of the cell), and an electrochemical gradient pushing K+ back into the cell (the cell is more negative on the inside). |
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Why is the cell membrane considered a capacitor? What is a capacitor?
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A capacitor is an insulator (lipid bilayer) separating two conductors (intracellular and extracellular solutions). Much like an electrical capacitor, charges are stored along the intra- and extracellular sides of the cell membrane. This is where resting potential is derived from.
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A container is divided in two by a membrane permeable to K+ only.
The left half of the container contains a much greater concentration of KCl than the right half. What will happen? |
K+ ions will migrate to solution of lower concentration. This will allow for negative charges (Cl-) to collect along membrane in the left-hand container.
As K+ travels to the right, positive charges (K+) will collect along the membrane of the right container. When charge buildup prevents anymore K+ from passing, there'll be no netflux of K+, regardless of its concentration. This is known as the NERNST EQUILIBRIUM |
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What is a logarithm?
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In mathematics, the logarithm of a number to a given base is the power or exponent to which the base must be raised in order to produce that number.
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log 1 = ?
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0
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log 100 = ?
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2
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log 1000 = ?
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3
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log 10 = ?
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1
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Provide the general equation for Nernst Equilibrium. Describe each constant.
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Eion = (-RT)/(ZF) * ln [ion]i/[ion]o
Z is valence of ion (CHARGE!!!) F = Faraday constant |
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Provide the equation for Nernst Equilibrium potential at body temperature.
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At 37 degrees C:
Eion = -61/Z * log Ci/Co C = [ion] |
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Assume:
[Na]i = 10 mM [Na]o= 100 mM Vrest = -70 mV What is the Nernst Equil Potential of Na? |
E of Na = -61/(+1) * log 10/100
=-61*log.1 =-61*-1 =+61 mV |
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What is the equation for determining the net driving force of an ion?
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Vmembrane - Eion
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Assume:
Vm = -70 mV E Na+ = +60 mV E K+ = -90 mV What would be the driving force of each ion? In which direction would each travel? Which would travel more forcefully? |
Driving Force = Vm - Eion
DF Na = -70 - +60 = -130 mV DF K= -70 - -90= +20 mV Na+ would enter cell, K+ would leave cell. Na+ would travel much more quickly! |
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What is E of Na+?
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+60 mV
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What is E of Cl-?
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-70 mV
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What is E of K+?
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-90 mV
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Would you need a negative or positive internal voltage (compared to outside of cell) to prevent Na+ from entering a cell? What would this say about the Nernst Equilibrium Potential necessary?
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Positive, and positve
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Would you need a negative or positive internal voltage (compared to outside of cell) to prevent K+ from leaving a cell? What would this say about the Nernst Equilibrium Potential necessary?
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Negative, and negative
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What is the flow of Cl- like at Vrest? Why?
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Not much flux, because Vrest ~ E of Cl- (-70)
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What is the E of Ca++? Why is this significant?
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+120 mV, this is really high, cells normally never get this positive, so cells can never have NO net flow of Ca++ when Ca++ channels open.
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Describe the relative number of Ca++ channels. Describe their transport.
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Not very many, very slow transport.
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What is the function of the GOLDMAN-HODGKIN-KATZ EQUATION? What does it demonstrate?
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Vm = -RT/F * ln [P(Na)*[Na inside]*P(K)*[K inside]*P(Cl)*[Cl OUTSIDE]/[P(Na)*[Na outside]*P(K)*[K outside]*P(Cl)*[Cl INSIDE]
At body temp: = -61 log (" ") Tells you Vm; demonstrates that the contribution of various ions to Vm depends on their relative permeabilities and concentration gradients. |
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Why are Vmembranes so close to E of K?
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Potassium is much more permeable to the membrane than any other cation. As such, Vrest is near E of K.
In short, ions with greatest cell permeability influence the membrane most |
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How are cells in a dynamic steady state?
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Ionic concentrations within cell remain the same in spite of a lack of equilibrium. Due to pumps/carriers fighting [ ] grads.
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What is reversal potential?
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The voltage at which there is no net flux of ions through an ion channel
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What is the reversal potential of a non-selective cation channel? What determines the potential?
What about for an ion channel selective for one ion? Two ions? |
0; determined by concentration gradient and permeability of ions passing through.
Would equal E of ion. Would be somewhere between the E of those two ions. |
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What's the main ion traveling through non-selective cation channels?
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Na+
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If P of Na were increased and the P value for all other ions were held constant, what would happen to the cell?
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Become depolarized
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