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NeurobioIogyI - Box 7-1 Box 7-1 The action potential...

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Box 7-1
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Box 7-1
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The action potential Threshold overshoot peak of AP repolarization after hyperpolarization refractory period All-or-none (I) Refractory period 1 msec.
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Imagine two compartments with equal concentrations of ions separated by a permeable membrane. 100 K + 100 Cl - 100 K + 100 Cl - K + K + K + K + K + K + K + K + Cl - Cl - Cl - Cl - Cl - Cl - Cl - Cl -
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Is there a potential difference (i.e.--voltage) across the two compartments? 100 K + 100 Cl - 100 K + 100 Cl - K + K + K + K + K + K + K + K + Cl - Cl - Cl - Cl - Cl - Cl - Cl - Cl -
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Is there a potential difference (i.e.--voltage) across the two compartments? NO! 100 K + 100 Cl - 100 K + 100 Cl - K + K + K + K + K + K + K + K + Cl - Cl - Cl - Cl - Cl - Cl - Cl - Cl - Each compartment is electroneutral (same # of positive and negative charges). There is no net difference in charge between the two compartments.
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Note: What is voltage? Voltage is the separation of charge between two points. The greater the difference in charge, the greater the voltage. It is a relative measurement.
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Do ions move freely from one compartment to the other? 100 K + 100 Cl - K + K + K + K + K + K + K + K + Cl - Cl - Cl - Cl - Cl - Cl - Cl - Cl - 100 K + 100 Cl -
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Do ions move freely from one compartment to the other? YES! 100 K + 100 Cl - K + K + K + K + K + K + K + K + Cl - Cl - Cl - Cl - Cl - Cl - Cl - Cl - Ions move by random (Brownian) motion. 100 K + 100 Cl -
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Is there a net movement of either ion from one side to the other? 100 K + 100 Cl - K + K + K + K + K + K + K + K + Cl - Cl - Cl - Cl - Cl - Cl - Cl - Cl - 100 K + 100 Cl -
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Is there a net movement of either ion from one side to the other? NO! 100 K + 100 Cl - K + K + K + K + K + K + K + K + Cl - Cl - Cl - Cl - Cl - Cl - Cl - Cl - 100 K + 100 Cl -
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Now imagine two compartments separated by a permeable membrane but with different concentrations of ions in each compartment (ignoring osmolarity). 200 K + 200 Cl - 100 K + 100 Cl - K + K + K + K + K + K + K + K + Cl - Cl - Cl - Cl - Cl - Cl - Cl - Cl - K + K + K + K + Cl - Cl - Cl - Cl -
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Is each compartment electroneutral? Is there a voltage across the two compartments? 100 K + 100 Cl - K + K + K + K + K + K + K + K + Cl - Cl - Cl - Cl - Cl - Cl - Cl - Cl - K + K + K + K + Cl - Cl - Cl - Cl - 200 K + 200 Cl -
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Is each compartment electroneutral? YES! Is there a voltage across the two compartments? NO! 100 K + 100 Cl - K + K + K + K + K + K + K + K + Cl - Cl - Cl - Cl - Cl - Cl - Cl - Cl - K + K + K + K + Cl - Cl - Cl - Cl - 200 K + 200 Cl -
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Is there a net movement of ions from one side to the other? 100 K + 100 Cl - K + K + K + K + K + K + K + K + Cl - Cl - Cl - Cl - Cl - Cl - Cl - Cl - K + K + K + K + Cl - Cl - Cl - Cl - 200 K + 200 Cl -
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Is there a net movement of ions from one side to the other? YES! 100 K + 100 Cl - K + K + K + K + K + K + K + K + Cl - Cl - Cl - Cl - Cl - Cl - Cl - Cl - K + K + K + K + Cl - Cl - Cl - Cl - Both K + and Cl - move down their concentration gradients, from the left compartment into the right compartment. 200 K + 200 Cl -
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What will the final concentrations be in each compartment? 100 K + 100 Cl - K + K + K + K + K + K + K + K + Cl - Cl - Cl - Cl - Cl - Cl - Cl - Cl - K + K + K + K + Cl - Cl - Cl - Cl - 200 K + 200 Cl -
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What will the final concentrations be in each compartment? They will be equal, i.e-- in equilibrium. 150 K + 150 Cl - 150 K + 150 Cl - K + K + K + K + K + K + K + K + Cl - Cl - Cl - Cl - Cl - Cl - Cl - Cl - K + K + K + K + Cl - Cl - Cl - Cl -
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Will this movement of ions create a voltage?
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