Week 2 Jonny - Week 2. Vertebrate Physiology 1/23/08...

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Week 2. Vertebrate Physiology 1/23/08 Diagram: There are anions inside the cell [DNA, proteins, sugars, etc.] It could be true that there are just as many K inside as there are outside. If the concentration of K inside is equal to the concentration of K outside. If you suddenly increase the permeability of the channel, then the potassium that is outside will be drawn into the cell. Over time, the amount of potassium inside will increase due to the anions inside the cell. However, the concentration gradient will change enough so that the potassium will be pushed out the other way. Secondly, assume there is potassium inside the cell and no potassium outside the cell. There are anions inside the cell and that inside the cell the concentration of anions equal the concentration of potassium, meaning there is no net charge inside the cell. Outside the cell, there is NaCl. If we took this cell and put a channel in it, the potassium wants to stay inside because of the anions inside, and the anions outside is already paired with a positive cation. However, the potassium will leave because of the differences in concentration. Every time that K leaves, there will an increasingly negative charge inside. This drives the potassium back in . These conditions lead to the equilibrium potential of Potassium ions. Equilibrium potential for a specific ion. - Equilibrium potential describes potential at which there will be no net flow of the ion because the forces driving it out equal the forces driving it into the cell. At rest, sodium has two gradients driving it in. Potassium has one driving it in (electrical) and one driving it out (concentration). However, at rest, only potassium flows to a negligible degree.* What are the effects, what is establishing, how much K has to flow before it stops having a net flow. 1
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- Use the Nernst Equation Summary: If we started out with a cell that had just as many cations as anions, then suddenly allowed potassium to flow in the gradient. There would be a deficit where there was a high concent. of K . - 68 mV – equilibrium potential for potassium. At extreme concentrations of potassium flow, the cell will have a resting potential of -86 mV. Establishing Equilibrium Potential – Series of Events 1. Separation of charges creates an electrical gradient a. Active (pumps) and Passive (selective permeability) processes – the major component that causes separation is the selective permeability of the membranes 2. This is the membrane potential (V m ) a. At some point at Eq. there will still be a flow. 3. Ions flow across membrane following the gradient 4. This flow creates a concentration gradient 5. Flow continues until the electrical gradient “balances” the concentration gradient 6. This V m is the equilibrium potential for that ion. Therefore:
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This note was uploaded on 08/25/2008 for the course BIO 365R taught by Professor Draper during the Spring '08 term at University of Texas at Austin.

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Week 2 Jonny - Week 2. Vertebrate Physiology 1/23/08...

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