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NPB 100 Fall 08 Exam 2

NPB 100 Fall 08 Exam 2 - Part 1(21 points correct...

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Part 1: (21 points, correct elimination 4 points, incorrect elimination –21 points). The following properties apply to the circuit shown below. ¾ Cell F has no spontaneous activity ¾ Cell F does NOT habituate ¾ Cell F has post-inhibitory rebound (through the cell E to Cell F synapse) ¾ Cell E has spontaneous activity ¾ Cell E habituates through the Cell D to Cell E synapse ¾ This habituation is through the D Æ E synapse so the longer D is on the less effective Cell E’s excitatory neurotransmitter receptor becomes ¾ Cell E does NOT have has post-inhibitory rebound ¾ Cell F’s inhibition onto cell E can completely shut down cell E including inhibiting and turning off spontaneous spikes ¾ Cell E’s spontaneous firing is at a low enough rate that it cannot counteract Cell D Æ F excitation ¾ D Æ F is a shorter length than D Æ E Which of the following can be the activity pattern of the circuit, when D fires as shown in the panels. Excitation Inhibition LEGEND (1) (2) (3) (4) (5) (6) E should not fire while F is There is no reason for E’s firing to increase since E does not have PIR Cell F does not habituate so this won’t work Cell E does not have PIR so this won’t work Because D--> F is shorter F will be excited by D before E F should not have spontaneous activity E should have spontaneous activity Cell E does not have PIR so this won’t work
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Part 2: (22 points, Very little partial credit will be given, do your best to get the correct answer). You find a neuron which at rest has the permeability and concentrations to the following ions. [Na +1 ] out = 145 mM [K +1 ] out = 5 mM [Cl -1 ] out = 120 mM [Br -1 ] out = 1 mM [Na +1 ] in = 15 mM [K +1 ] in = 175 mM [Cl -1 ] in = 12 mM [Br -1 ] in = 10 mM PNA = 100 PK = 4000 PCl = 1000 PBr = 1 On the dendrite of this neuron is a neurotransmitter receptor that when opened is equally permeable to Cl -1 and Br –1 and is not permeable to any other ion type. What is the reversal potential of this receptor? Common wrong answers 57.5 This is the bromide equilibrium potential and is wrong -57.5 This is the chloride equilibrium potential and is wrong 0 while halfway between the fluoride and chloride equilibrium potentials you need to do the GHK to get the right answer. You might note that the real answer (-42.6) is closer to the chloride equilibrium potential. This is largely due to the fact that the concentrations of Fluoride are much lower overall than those of Chloride. The following is wrong because you are calculating the resting membrane potential of the entire cell and not the reversal potential of the channel . Other permeability combinations are also wrong for example Adding 1 to PCl so its 1001 and 1 to PBr so its 2 and still using Pna=100 and PK = 4000 is wrong and would give –71.7 mV.
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