study_questions_for_the_final_exam_key

study_questions_for_the_final_exam_key - 1a. Would a 2...

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1a. Would a 2 point discrimination task be easier on your lips or on your back? Lips 1b. Explain your answer to 1a. The magnification factor in the cortex is very large for the lips, so there are very many cortical cells responding to touching the lips, so the lips are more sensitive. Also, there are many more receptors in the periphery on the lips, and therefore these receptors have smaller receptive fields, so they can resolve stimuli that are very close together (for full credit you would have to mention both reasons) 2a. You record from a cell where repeated firing of a synapse causes an increase in the size of the excitatory post-synaptic potential. What is this process called? Sensitization or facilitation or potentiation (any one of these would be considered correct) 2b. Describe in as much detail as you can the cellular mechanism underlying this process. Residual calcium theory. Calcium entering the cell during previous action potentials is mostly removed from the cytoplasm, but a small amount remains. Because the probability of neurotransmitter release is proportional to [Ca++] 4 , this effect is very non-linear, so a small amount of residual calcium can have a big effect on the amount of transmitter released (by greatly increasing the number of vesicles binding), and therefore on the increased size of the EPSP. 3a. How would you calculate the membrane potential of a cell? Use the GHK Equation RT/F(p K +[ K + ] o + p Na + [Na+] o + p Cl - [Cl - ] i ) /( p K +[ K + ] i + p Na + [Na+] i + p Cl - [Cl - ] o) 3b. A cell’s membrane potential is –70 mV, and the concentration of chloride is equal inside and outside of the cell. If you apply neurotransmitter which opens a ligand-gated chloride channel, will the post-synaptic potential be hyperpolarizing or depolarizing? Depolarizing. 3c. Explain your answer to 3b.
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From the Nernst equation, the fact that the chloride concentration inside is the same as the chloride concentration outside means that the equilibrium potential for chloride is 0mV (because ln(1) = 0 ). Opening a channel permeable only to chloride will tend to push the membrane potential toward the equilibrium potential for chloride. Since the chloride equilibrium potential is more positive than the resting membrane potential, the post-synaptic potential will be depolarizing. 4a. What is the smallest number of cells that can produce a rhythmic firing pattern? One 4b. Describe (in as much detail as you can) the cellular mechanisms which underlie this type of rhythmic firing. The cell is spontaneously active. The depolarization of the action potentials opens voltage gated calcium channels. Increased intracellular calcium opens calcium gated potassium channels. Potassium leaves the cell, causing the cell to hyperpolarize below threshold and stop firing action potentials. The voltage gated calcium channels then close (due to the hyperpolarization). Because
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This note was uploaded on 05/04/2008 for the course NPB 100 taught by Professor Chapman during the Spring '08 term at UC Davis.

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study_questions_for_the_final_exam_key - 1a. Would a 2...

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