sample_midterm_3_2006_key

sample_midterm_3_2006_key - YOUR NAME_ Social Security #_...

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YOUR NAME__________________________ Social Security #_________________ GO ON TO NEXT PAGE!!!! 1 Your signature______________________ NPB100 Spring Quarter 2006 Midterm 3 Please check this box if you do not want your exam returned in the bins in the hallway… Question Score Total 1 7 2 15 3 16 4 15 5 12 6 5 7 10 8 9 9 3 10 8 TOTAL 100
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YOUR NAME__________________________ Social Security #_________________ GO ON TO NEXT PAGE!!!! 2 Question 1. (Total Points 7) Why do photoreceptors have a higher metabolic rate while you sleep than they do during the daytime? In darkness, photoreceptors have a constant “dark current”, with sodium entering the outer segment and potassium leaving the inner segment. The sodium/potassium ATPase (which requires energy in the form of ATP) has to be very active in the dark to maintain ion concentrations across the membrane given this dark current. Therefore the photoreceptor has to have a very high metabolic rate in the dark in order to make enough ATP to keep the sodium/potassium ATPase working. During the daytime, light hyperpolarizes photoreceptors, reducing the dark current. Therefore the sodium/potassium ATPase does not need to work as hard in the light to maintain the ionic concentrations, and the cell’s metabolic rate can be lower because it does not need to make as much ATP. Question 2. (Total Points 15) 2a. (12 pts) Considering only the OFF pathways in the retina, fill in the diagram below to show the activation of the direct and indirect pathways (use + to show excitation, – to show inhibition, and 0 to show no effect). Then plot the ganglion cells’ response levels below. Light Dark Responses (note that lateral inhibition is not as strong as direct excitation) - 0 2b. (3pts) Briefly explain how lateral inhibition in the retina emphasizes edges. Lateral inhibition, as shown above, means that there is an amplification of the difference between the firing rates of retinal ganglion cells at a light/dark edge. This results in there being a larger perceived difference in the light versus the dark than actually exists. Therefore we see edges as being more pronounced than they really are.
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YOUR NAME__________________________ Social Security #_________________ GO ON TO NEXT PAGE!!!! 3 Question 3. (Total Points 16) 3a. (3 pts) Increasing the K+ concentration in the endolymph (the fluid surrounding the
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sample_midterm_3_2006_key - YOUR NAME_ Social Security #_...

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