sample_exam_2003_sol

sample_exam_2003_sol - Print Name _ _ pg. 1 of 11 Part 1....

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Print Name __________________ ____ pg. 1 of 11 Intensity (dB) Part 1. (Total 2 points) Refer to neurons 1 and 3, whose tuning curves are shown below Neuron 4 receives input from neurons 1 and 3. The synapse from neuron one to 4 ( neuron 1 Æ neuron 4 synapse ) is mediated by neurotransmitter receptors on neuron 4 that, when neurotransmitter binds to them, open sodium channels . The neuron 3 Æ neuron 4 synapse is mediated by neurotransmitter receptors on neuron 4 that, when neurotransmitter binds to them, open sodium and chloride channels with relative permeabilties of 0.4 for sodium and 0.6 for chloride . Given the following permeability and concentrations for the fluids around the synapses onto cell 4. [K + ] out = 15 mM [Na + ] out = 600 [Cl - ] out = 625 [K + ] in = 650 mM [Na + ] in = 100 [Cl - ] in = 100 At rest Pk = 1 At rest Pna = .11 At rest Pcl = .12 AP threshold = -22 mV ? Legend Denotes synapses that we do not tell you whether they are excitatory or inhibitory Neuron 3 ? ? Neuron 1 Neuron 4 5 10 15 20 0 20 40 60 80 Neuron 1 : CF = 5 kHz 5 10 15 20 0 20 40 60 80 Neuron 3 : CF = 15 kHz Frequency (kHz) Frequency (kHz) We will not look in this box!!!
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Print Name __________________ ____ pg. 2 of 11 Intensity (dB) The reversal potential for the neuron 1 Æ neuron 4 synapse (45 mV) is > than AP threshold (-22 mV). .4*100+.6*625 = -8 mV Therefore this is excitatory. The reversal potential for the neuron 3 Æ neuron 4 (-8 mV) is > than AP threshold (-22 mV). Therefore this is excitatory. So we just merge the 2 excitatory areas Common mistakes: The most common mistake was thinking that whether a synapse is inhibitory or excitatory depends on whether the cell hyper- or depolarizes from rest. This is wrong. As emphasized in lecture (from 10/22/03, pages 1,7, 11,12 ), and gone over on question 1.2 of exam 2, question 1.2 of late discussion section quiz 4-- whether a synapse is inhibitory or excitatory depends on the reversal potential of the receptor and the action potential threshold Another common mistake was just assuming because it was sodium that it was excitatory. You need to know the reversal potential to properly explain this answer. . Note: space is provided below the multiple-choice question to explain and show your math. 1.1 (0.7 Points) Which of the following is the tuning curve of cell 4 (note dark shaded areas are inhibitory, and un-shaded outlined areas are excitatory). There are areas that appear both excitatory and inhibitory (in C and F); this is OK because more information would be needed to determine which input was stronger in these potentially overlapping areas. 1.2 (1.3 Points) Explain your answer (show math below): __________________________________ _____________________________________________________________ _____________________________________________________________ _____________________________________________________________ Show math For neuron 1 Æ 4 Er = 57.5/z*log([Na] out /[Na] in ) = 57.5*log(600/100) = 45 mV For neuron 3 Æ 4 Er = 57.5 *log C 5 10 15 20 0 20 40 60 80 A. 5 10 15 20 0 20 40 60 80 Frequency (kHz) Frequency (kHz) 5 10 15 20 0 20 40 60 80 Frequency (kHz) 5 10 15 20 Frequency (kHz) 0 20 40 60 80 B 5 10 15 20 0 20 40 60 80 Frequency (kHz) 5 10 15 20 0 20 40 60 80 Frequency (kHz) D E F .4*600+.6*100
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Print Name __________________ ____ pg. 3 of 11 Part 2 ( Total 2.8 points ). Below are the tuning curves of 3 primary auditory cortical neurons. All the tuning curves have identical shape and thresholds; they are just shifted in characteristic frequency (CF, also called best excitatory frequency in the book).
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sample_exam_2003_sol - Print Name _ _ pg. 1 of 11 Part 1....

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