Lecture 03 - Membrane Potentials and Neurons

Lecture 03 - Membrane Potentials and Neurons - Lecture 3...

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Lecture 3 - Membrane Potentials and Neurons Membrane Potential (Fig 4.2) 1. Under normal conditions, the inside of a cell is -70 mV relative to the outside. Concentration of Selected Solutes (Table 4.1) Solute Intracellular Fluid Extracellular Fluid K + 140.0 4.0 Na + 15.0 145.0 Mg 2+ 0.8 1.5 Ca 2+ <0.001 1.8 Cl - 4.0 115.0 HCO 3 - 10.0 25.0 P i 40.0 25.0 Amino Acids 8.0 2.0 Glucose 1.0 5.6 ATP 4.0 0.0 Protein 4.0 0.2 1. This difference in concentration results in the negative resting potential. At Time 0, Membrane Potential Is Zero (Online Slide 2) 1. The Cl - ions are trapped on the left of the membrane. Only K + can go through. At Time 1, Membrane Potential Is Slightly Negative (Online Slide 3) 1. Some K + begins to leak across the membrane. 2. This leaves a net negative charge on the opposite side where Cl - is more concentrated. 3. The movement of K+ ions is controlled by a concentration gradient as well as an electrochemical gradient. a. The concentration of K + wants to reach equilibrium. b. As soon as the K + moves away from the Cl - , it is attracted back due to their charges. At Equilibrium, Membrane Potential Is E K (Online Slide 4) 1. At this time, both sides have reached equilibrium as far as their electrical and chemical gradients are concerned. Nernst Equation Cell 1: Permeable To K + Only (Fig 8.6) 1. K+ is highly concentrated inside the cell, so it would all flow out. 2. This makes the inside partially negative since the positive charge is flowing out. 3. The chemical force is outward while the electrical force is inward.
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