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15 Cards in this Set
- Front
- Back
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Ohm's law described |
I=g*E, where E = voltage E=IR; g=1/R = permeability - circuit needs a resistor and battery |
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resistance (R) |
resistance = volts/current - how hard it is to get across |
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conductance (g) |
conductance = permeability = 1/R - how easy it is to get across |
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membrane capacitance |
- good insulator = membrane - good conductor = intracellular and extracellular fluid - membrane capacitance passively stores electrical charge |
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charge equation (Q) |
Q=C*E charge = capacitance*voltage - capacitance is proportional to the area of conductors - charge increases as area is increased - capacitance increases as diameter increases |
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relationship of capacitance to: area distance b/w plates material b/w plates |
1. area and capacitance = positively correlated 2. bistance b/w plates (e.g. myelin) and capacitance = negatively correlated 3. material b/w plates and capacitance = ?? |
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Time constant |
tau = the time it takes voltage to decay to 37% of its final voltage - function of resistance and capacitance |
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Capacitor in a cell |
- begins as a short circuit with zero impedance (so meter = 0) - as charge accumulates, current begins to flow through resistor and meter reads a voltage (no longer a short circuit) - once capacitor is fully charged, no additional current flows to the capacitor and all current goes through resistor |
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capacitor charging or discharging effects |
- because the membrane is a capacitor, there is a delay as it charges or discharges - delay increases as the area of membrane increases (although it can hold more charge overall) |
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equilibrium (membrane resting potential) |
net charge = 0 no energy is needed to maintain the cell Ek=(RT)/(zF)*ln(ko/ki) = Nernst |
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RC current |
- current across the resistor = membrane potential - you need voltage across the resistor to get a current: Ir=g(Em-Ek) current = conductance * driving force |
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what is the current once capacitor is charged? |
- once capacitor is charged, Ir=g*Em |
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what is current before capacitor is charged? |
Ir=g(Em-Ek)current = conductance * driving force |
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IV-curve plot |
Em (voltage) = x-axis current = y-axis g= slope of line and gives indication of how many channels are open (1g = 1 channel, 3g = 3 channels, etc) |
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what happens when g (conductance) is not constant? |
- conductance becomes a function of voltage and plot is not linear - when g increases, current must increase to keep voltage the same I=g*Em (membrane resting potential in volts) |
