Bi150 PS3_Answers_2011

Bi150 PS3_Answers_2011 - PS3 Answer Key Problem 1. Synaptic...

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PS3 Answer Key Problem 1. Synaptic integration (1.5 points) A. (0.9 point) Inhibition Many inhibitory synapses in the CNS utilize GABA A and glycine receptors. Both GABA A and glycine receptor channels are permeable to Cl - ions. Calculate the Nernst potential for Cl - ions, E Cl , at 25 ° C. Consult the ionic concentrations on slide 5 of lecture 1. E Cl = -25*ln(110/10) = -60mV (or -58*log(110/10) = -60mV). Resting membrane potentials of neurons are sometimes close to E Cl . When this is the case: a. How does the membrane voltage change if only GABA A receptors are activated? There is no change in membrane potential. When the membrane potential is equal to E Cl , no current flows Consider a neuron receiving two excitatory inputs as shown below. The traces at the right show the membrane potential in the soma without inhibition. i) excitatory input 1 is stimulated alone ii) excitatory input 1 & 2 are stimulated b. For each trace, redraw the trace, then superimpose the trace if a GABAergic input is active at location A during the excitatory stimuli. c. For each trace, redraw the trace, then superimpose the trace if a GABAergic input is active at location B during the excitatory stimuli. In bottom figures, blue : EPSP traces by input 1 alone 1 + 2 A B E x c i t a t o r y i n p u t 1 E x c i t a t o r y i n p u t 2 I n h i b i t o r y i n p u t 1 a l o n e 1 + 2 V t i m e s o m a d e n d r i t e 1 a l o n e V t i m e i) ii)
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PS3 Answer Key green : EPSP traces by input 1+2 . The left figure shows EPSPs without inhibition. The middle figure shows EPSPs with inhibition at location A. The right figure shows EPSPs with inhibition at location B. As figures indicate, inhibition at location A efficiently blocks excitation 2, but has little effect on excitation 1. On the other hand, inhibition at location B blocks both excitation 1 and 2 efficiently. B. (0.6 point) Active dendrites The figure below shows simultaneous recordings of membrane potential from the soma and dendrite when the action potential is induced by current injection into the soma (panel A shows recording sites, and panel B shows membrane voltage). a. Redraw the dendritic traces; then superimpose the dendritic voltage trace during action potentials in a mutant animal that lacks “dendritic” voltage-gated Na + channels. Explain. Dendrite Soma A B V time The amplitude of dendritic potential is much lower, given there is no regenerative current due to lack of Na+ channel. But there should still be passive spread.
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PS3 Answer Key b. What is Spike Timing Dependent Plasticity, STDP? STDP refers to functional changes in neurons at the synapses that are sensitive to the timing of action potentials. STDP can result from: presynaptic spikes preceding postsynaptic spikes (pre-post spiking), giving rise to long-term potentiation (LTP) postsynaptic spikes preceding presynaptic spikes (post-pre spiking), giving rise to long-term depression (LTD) c. How might backpropagating spikes, due to dendritic sodium channels, influence synaptic plasticity? The back propagation of action potentials (from soma to dendrites) is important to open NMDA
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This note was uploaded on 01/03/2012 for the course BI 150 taught by Professor Kennedy,m during the Fall '08 term at Caltech.

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Bi150 PS3_Answers_2011 - PS3 Answer Key Problem 1. Synaptic...

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