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18 Cards in this Set
- Front
- Back
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Electrochemical Driving Force |
(Vm - EK) |
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Ohm's Law |
IK = gK * Vm |
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Modified Ohm's Law |
At steady state: IK = gK( Vm - EK) Because at steady state we know current is 0 and we also know the net electrochemical driving force is balanced at 0. |
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At steady state, what is the net current of all ions? What is the net electrochemical driving force? |
They are both zero. There is no net flux of ions at a steady state |
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gK : gNa: gCl relative conductances |
8:1:2 |
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How do you estimate Vm with the driving force of each ion? |
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Conductance (g) |
the reciprocal of resistance (R) |
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Outward current (positive or negative?) |
= positive current |
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Inward current is positive of negative? |
negative current |
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Membrane potential Vm |
is the potential inside the cell measured with respect to the outside. The potential outside is defined as zero. |
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Current (I) |
Simply defined as electrical flow. By convention, positive current is considered to flow in the direction of positive charge carriers.
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Voltage |
is the electrical force of pressure that makes charge carriers move. Voltage (V or sometimes E) is also referred to as "potential". Voltage is always measured as a difference between two places |
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Voltage (pressure) can produce current (flow) only when |
there is a conductive pathway, like an ion channel. |
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Current is proportional to the |
voltage difference and the conductance of the pathway. This is what is stated in Ohm's law
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leakage conductance |
The aggregate conductance of all channels at rest. The potassium selectivity of the leakage conductance accounts for the transmembrane voltage of the cell at rest (resting Vm) |
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Voltage-activated _____ channels produce positive feedback and the all-or-none action potential |
Sodium |
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When sodium channels open during an action potential, what happens to gNa? |
gNa goes up. It's the conductance, so the more open channels, the greater gNa becomes. |
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What makes action potentials all-or-none? |
They either fire when the cell is depolarized beyond the threshold, or they do not fire if the cell is depolarized but is below threshold. For instance, if threshold is -45mV, depolarizing to -44mV will cause the voltage-gated Na channels to open, further depolarizing the cell towards Na's reversal potential. If the cell is depolarized to -46mV, the cell will not fire an action potential and will simply return to the resting Vm. |
