Prob Set 6 Q&A - Problem Set 6 Cellular...

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1 Problem Set 6 Cellular Neurobiology Fall 2010 1. Two action potentials arrive in the presynaptic terminal 10 msec apart. Would you expect to the elicited PSPs at the synapse to be of the same size? If not, why not? What mechanisms could account for this? The two PSPs may differ in size, depending on the levels of intracellular calcium attained and on the probability of release (p), i.e. how efficient the process was initially. If p is low, then the second PSP may be larger due to the buildup of calcium (residual from the first AP adding to the usual amount coming in from the second AP). The increased calcium increases the p value and therefore enables more release in reponse to the second AP (= paired pulse facilitation). Alternatively, if p is high initially, most of the “docked” SVs will have been released by the first AP, and time is needed to refill the sites with new SVs in order to repeat the release event. If the second AP arrives before this occurs, it will not be able to elicit as many, hence a decreased PSP results (= paired pulse depression). 2. Describe the arrangement of excitatory pathways comprising the hippocampus (input, relays, output), and indicate the experiment procedure to induce and record LTP in CA1 pyramidal neurons. Input to the hippocampus comes from the entorhinal cortex, mediated by preforant pathway fibers exciting granule neurons in the dentate gyrus via glutamatergic synapses. The granule neurons, in turn, extend mossy fibers to pyramidal neurons in the CA3 region, forming excitatory glutamatergic synapes on them, and those pyramidal neurons extend axons comprising the Schaffer collaterals to innervate pyramidal neurons in the CA1, exciting them again via glutamatergic synapses. The CA1 pyramidals project axons out of the hippocampus, relaying information to other brain regions, and thereby represent the hippocampal output.
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