EBME201 Exam2_2007_B

EBME201 Exam2_2007_B - 1) Explain how depolarization of the...

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1) Explain how depolarization of the membrane causes voltage gated Na+ channels to open. Make sure to include a description and/or diagram showing the structural parts of the channel that are affected by the voltage change and what happens to them when the membrane depolarizes. –hlc (4pts total) Positively charged alpha helical sections of the channel get repelled outward as the membrane starts to depolarize. The movement of these positively charged segments pulls on other parts of the polypeptide chains causing them to move and unblock the channel. (see figure 9-16 Kandel) 2) When an action potential reaches the synaptic terminal, __ voltage(2pt) __-gated __ Ca++(1pt) ___ channels open causing ___ Ca++(1pt) ______ions to flow into the cell. This triggers __ vesicles(2pt) ________to fuse and release neurotransmitters. The neurotransmitters then diffuse across the synaptic cleft where they can bind to _ ligand(2pt) ___gated ion channels in the postsynaptic cell .-hlc (8pts total) 3) Why do action potentials generally start at the axon hillock? What is special about that part of the membrane? -It has a high density of voltage gated Na + channels (3points) (Scott) 4) Individual voltage-gated ion channels: a) change their conductance as the potential across the membrane changes b) change their probability of being open as the potential across the membrane changes- hlc (2pts) c) both a & b d) none of the above 5) Action potentials travel faster along ___ myelinated(1pt) ___(myelinated,or unmyelinated) axons. Action potentials travel faster along _ larger(1pt) _____(larger or smaller) axons. Explain how axon diameter and myelination effect how fast an action potential will travel along an axon. –hlc (2pts total above, 3pts total below) 1.) The larger diameter reduces axial resistance(less resistance/more speed). Therefore current will flow farther down the inside of the axon before exiting through the membrane.(1.5pts) 2.) Myelination increases membrane resistance which cause more current to flow down the inside of the axon before exiting at gaps between the myelin(Nodes of Ranvier). By forcing more current to travel down the axon before leaving the cell, the current will depolarize the membrane farther down the axon compared to smaller or unmyelinated axons. (1.5pts)
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6) When using a voltage clamp on a section of an axon, what primary electrical parameter does the experimenter control?______ Voltage ________ (2 points) ______. Which electrical parameter is then directly measured by the experimenter?____ Current (2 points) _______________. Which parameter can then be calculated from the other electrical parameters you have measured or defined?__ Conductance or Resistance (2 points) __________. If you add a Na+ channel blocker to the extracellular solution, which of the above parameters would change? -Both current and conductance (resistance) would change (3points; 1.5 each)
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This note was uploaded on 10/13/2008 for the course EBME 201 taught by Professor Dawntaylor during the Spring '08 term at Case Western.

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EBME201 Exam2_2007_B - 1) Explain how depolarization of the...

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