320Fall08Midterm2_Key_v2 - BIO320Dr.Bushart MidtermExam#2...

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BIO 320 Dr. Bushart Print Name:___________________________ Midterm Exam #2 12:30 PM Tuesday October 14, 2008 General instructions: Read each question carefully and don’t hesitate to ask if a question seems unclear. Trying to provide an answer for every question is advantageous; you will not be penalized for guesses. Write a clear concise answer for each question. Some questions may have more than one possible answer but require you to defend your choice. The questions have specific answers, although for some, more than one answer is possible. If possible, answer each question in the space provided, but if needed, continue on the back. If you use a drawing as part of your answer, be sure to also include appropriate labeling and/or a short written explanation. Use pen if you want a chance for a regrade. This exam is 5 pages long and worth a total of 100 points (the points for each section/question are noted in parentheses). To receive full credit you must clearly and fully answer the question being asked. Partial credit may be given in 0.5 point increments. Be sure you include clear explanations in your response. Make sure your response answers the question being asked! 1. It important that most ion channels are not gated by more than one stimulus. Consider what would happen if a neurotransmitter receptor (ligand-gated channel) was also sensitive to membrane potential. a. Explain how neuronal computational would be altered if our receptors had this dual-gating property. The amount of depolarization in a PSP event is normally tied directly to the quantity of or the duration of exposure to neurotransmitter. Dual-gated receptors could be influenced by depolarization events at neighboring synapses, which would ruin the ability of neurons to calculate spatially combined PSPs. Alternatively, these channels may also experience runaway activation with a minimal amount of transmitter, building to a strong temporal-style PSP. Either explanation results in the inability of the neuron to properly respond based on the incoming signals (the responses will likely be hypersensitive). My intent was that the channels could be gated by either stimulus; however, this question can be interpreted to mean that the channels require both stimuli simultaneously . In that case, these receptors would likely not be stimulated at all, since initial ligand-gating is what normally depolarizes the membrane in the first place. A lack of channel opening is going to prevent the neuron from ever producing APs, so neuronal computation would be pretty much non existent. b. Would neurons with these dual-gated receptors be impaired in their ability to undergo adaptation? Why or why not? The adaptation response is not tied directly to the receptors themselves, but is a system involving voltage- and Ca2+-gated channels which are activated in response to rapid and prolonged action potentials. So, even with altered receptors, the neurons should still be able to undergo the adaptation response. 2.
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320Fall08Midterm2_Key_v2 - BIO320Dr.Bushart MidtermExam#2...

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