Prob Set 4 Q&A

Prob Set 4 Q&A - Problem Set 4 Cellular...

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1 Problem Set 4 Cellular Neurobiology Fall 2010 1. Explain the differences in the synthesis and axoplasmic transport of small-molecule neurotransmitters versus peptide neurotransmitters. Small molecule neurotransmitters (e.g. acetylcholine, glutamate) are synthesized locally at the presynaptic terminals. The enzymes necessary to synthesize the neurotransmitters are made in the cell body and transported to the terminal via slow axonal transport. At the terminal, the enzymes synthesize the neurotransmitter from precursors (e.g. acetylcholine from the acetyl moeity of acetyl-CoA and free choline). Peptide neurotransmitter (e.g. oxytocin, vasopression) precursors and enzymes are together synthesized at the cell body and packed in vesicles. The vesicles move via fast axonal transport along microtubules and reach the presynaptic terminal. There the enzymes modify the precursors within the vesicle to prepare the final neurotransmitter for release. 2. Are EPPs an all-or-nothing event like action potentials or are they graded events? Explain. How was this feature of EPPs identified? EPPs are graded events that are proportional to amount of transmitter (acetylcholine) released onto the NMJ, and this, in turn, is determined by the number of synaptic vesicles synchronously exocytosed to release transmitter from the motor nerve terminal. Each vesicle represents a quantum, and toghether they determine the quantal content of the EPP. The graded nature was established by combining several observations. These included (a) the discovery of small spontaneous potential changes that occurred without presynaptic stimulation and had the shape of EPPs (termed miniature EPPs or mEPPs), (b) the discovery that reducing extracellular calcium reduced the size of the EPP and revealed quantal fluctuations in EPP amplitude with the size of a guantum being equivalent to the size of a mEPP, and (c) drugs that blocked acetylcholine receptors at the NMJ (e.g. curare)
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This note was uploaded on 12/09/2010 for the course BIPN BIPN 140 taught by Professor Spitzer during the Spring '07 term at UCSD.

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Prob Set 4 Q&A - Problem Set 4 Cellular...

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