NeurobioIogyI - Box 7-1 Box 7-1 The action potential • Threshold • overshoot • peak of AP • repolarization • after hyperpolarization •

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Unformatted text preview: Box 7-1 Box 7-1 The action potential • Threshold • overshoot • peak of AP • repolarization • after hyperpolarization • refractory period • All-or-none (I) Refractory period 1 msec. 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- 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- 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. 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. 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- 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- 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- 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- 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- 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- 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- 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- 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....
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This note was uploaded on 03/28/2012 for the course BIO 49593 taught by Professor Wanser during the Spring '10 term at University of Texas at Austin.

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NeurobioIogyI - Box 7-1 Box 7-1 The action potential • Threshold • overshoot • peak of AP • repolarization • after hyperpolarization •

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