Sodium-Potassium Pump and Action Potential: Effects of Ion Concentration Changes, Assignments of Biology

Download Sodium-Potassium Pump and Action Potential: Effects of Ion Concentration Changes and more Assignments Biology in PDF only on Docsity! Homework #6 Solutions Due October 12, 2004 1. The mechanism described in this paragraph assumes the positive charge in the cell is due to the electrical signal, however, the electrical signal causes the initiation of the sodium potassium pump. The stimulus causes the sodium channels to open, and the pumping of sodium ions into the cell raises the potential of the cell to positive. Then the pumping of potassium out of the cell returns the cell to its negative resting state. 2. a. Experiment 2 shows the results for changing intracellular sodium concentration. Note that the resting membrane potential is not changed appreciably, but the peak of the action potential (which approaches the Nernst equilibrium potential for sodium) is changed appreciably. The Nernst equilibrium potential for sodium is V NA = (RT/F) ln (co/ci). Hence the largest value on intracellular sodium concentration corresponds to the lowest Nernst equilibrium potential. Therefore, curve 3 must correspond to the highest intracellular concentration. b. Experiment 1 shows the results for changing extracellular potassium concentration. Note that the resting potential is changed appreciably, the peak of the action potential is not changed much, and the undershoot of the action potential (which approached the Nernst equilibrium potential for potassium) is changed appreciably. The Nernst equilibrium potential for potassium is V K = (RT/F) ln (co/ci). Thus the largest value of the Nernst potential for potassium occurs at the highest value of the extracellular concentration. Therefore, the curve 1 must correspond to the highest extracellular potassium concentration.