03 Quiz info

03 Quiz info - LESSON 3 QUIZ INFORMATION AND EXPLANATIONS...

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Unformatted text preview: LESSON 3 QUIZ INFORMATION AND EXPLANATIONS FOR SELECTED QUESTIONS The average for Lesson 3 Quiz was 84.5% and the distribution of scores is illustrated in the histogram below Six students scored 90% or above!!! Below are some explanations to the more difficult questions. If you have further questions about these or others, please post them in the Lesson 3 Discussion Forum or email me. If you missed any of the questions on this quiz, you may benefit from reading these explanations . Many of the questions in this quiz can be answered by using the Very Important Principles found in Part 6 of Lesson 3 Outline. If you understand these principles and can apply them, most of the difficult parts of membrane electrophysiology will become easy!! These Very Important Principles (VIPs) are summarized below. If you are considering the effects of changes in the chemical gradients, use the following principles. Very Important Principle #1: Changes in the chemical gradient of a given ion will change the equilibrium potential (E ion ) for that ion. Very Important Principle #2: The membrane potential (E m ) is highly sensitive to changes in the chemical gradient, and therefore the equilibrium potential, of the most permeable ion. The Goldman equation takes into account the relative permeabilities. If you are considering the effects of changes in permeability (opening and closing of ion channels), use the following principles. 1 Very Important Principle #3: If the permeability of the membrane to a given ion increases, the membrane potential will move closer to that ions equilibrium potential. Very Important Principle #4 : If the permeability of the membrane to a given ion decreases, the membrane potential will move away from that ions equilibrium potential. A corollary to Very Important Principles #3 and #4 : If E m is equal to an ions equilibrium potential, there will be NO net diffusion of that ion and no change in E m , no matter how permeable the membrane becomes to that ion. Questions 1 - 8 For questions 1 through 8, use the following hypothetical situation. Assume that the cells in the questions have these concentration gradients for the ions. Extracellular mM Intracellular mM Eion A + 2 200-123 B + 300 30 61.5 C ++ 30 1 45.4 D- 300 30-61.5 Now, before you even start looking at the questions, I strongly suggest that you ALWAYS draw the information provided on a voltage as a function of time graph (below). Ive put the information provided in the following graph. Note the actual membrane potential, the voltage (E m ) across the membrane, is not provided. Only the equilibrium potentials for various ions were given. 2 So, with the situation illustrated, lets look at a few of the questions....
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03 Quiz info - LESSON 3 QUIZ INFORMATION AND EXPLANATIONS...

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