Lab Problem Set #2 answer key PDF

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1. 2The'trace'of'a'typical'action'potential'is'given'to'the' right.'' ' (i) For'each'phase'of'the'action'potential,'fill'in'the' table'below'to'indicate'whether'the'conductance' of'the'cell'to'Na+'and'K+'is'higher'and'the'state'of' V-gated'Na+'and'K+'channels'(opening,)open,) closed,)closing,)inactivated).' ' ' Phase)

Name)of)Phase)

1)

' Rest'

' gK '

2)

Depol/synaptic' input'

' gNa'

3)

' Rising'phase'

' gNa'

' Falling'phase' ' Undershoot' '

' gK ' ' gK '

4) 5)

V-gated)Na+)channel)state) V-gated)K+)channel)state) Closed'(deinactivated' ' acceptable)' Closed' ' ' ' Opening' Closed' ' ' ' ' Open' Closed'(Opening' acceptable)' ' ' Inactivated' Open' Closed'(deinactivated' ' acceptable)' Open'(Closing'acceptable)'

gNa)or)gK)higher?)

' (ii)'What'point'on'the'graph'corresponds'to'a'time'within'the'absolute)refractory)period?'(circle'one)' ' ' ' '''''' ' ' ' ' '

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(iii)'What'point'on'the'graph'corresponds'to'a'time'within'the'relative)refractory)period?'(circle'one)' '

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2.'You'are'studying'a'neuron'that'has'initiated'an'action'potential'(AP)'that'is'now'racing'along'its'myelinated' axon'at'a'steady'rate.' ' a.'The'AP'reaches'a'stretch'of'axon'that'is'suddenly'unmyelinated.'What'happens'to'the'conduction' velocity'(speed'of'the'AP)'in'this'portion'of'the'axon'(Increases,)Decreases,)or)No)Change)?)(circle)one))

' ' b.'The'AP'continues'along'the'unmyelinated'part'of'the'axon'and'reaches'a'part'where'the'diameter'of' the'axon'suddenly'gets'much'larger.'What'happens'to'the'conduction'velocity'(speed'of'the'AP)'in'the'wider' portion'of'the'axon'(Increases,)Decreases,)or)No)Change)?)(circle)one)) 3.'In'each'of'the'panels'below,'to'the'left'is'an'action'potential'trace'from'a'normal'cell'generated'by'injecting' just%enough'depolarizing'current'to'reach'threshold.''For'each'of'the'questions'below,'draw'what'you'think'an' action'potential'would'look'like'in'response'to'the'same'current'pulse'after'you'experimentally'mutate'the' neuron'to'yield'conditions'A-D.'The'changes'should'be'relative'to'the'typical'action'potential'given'to'you.' ' A.'Voltage-gated'K+'channels'open'faster'' ' ' B.'Leak'channels'slightly'more'permeable'to'Na+,' ' Reduced'overshoot,'narrower'AP''''''''''''''''''''''''''''''''''''''''''''' ' ' ' gK'still>'gNa'' ' ' ' '

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increased'resting'potential'

' ' C.'Threshold'of'voltage-gated'Na+'channels'is'higher''

D.'#'of'Voltage-gated'K+'channels'is'reduced'

No'AP:'original'depolarizing'current'was'“just'enough”' '

slower'falling'phase,'reduced'undershoot'

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' ' 4.'A'typical'neuron'is'made'permeable'to'only'Na+'and'K+.'Assume'EK'='-80'mV,'ENa'='+55'mV,'and'Vm'='-65' mV'' (Circle)the)bolded)words)that)best)complete)the)sentences)below))' '

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a.'The'driving'force'for'Na+'is'(the)same/larger/smaller)'than'the'driving'force'for'K+'

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b.'At'rest'the'conductance'for'Na+'is'(the)same/larger/smaller)'than'the'conductance'force'for'K+''

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c.'If'[K+]out'increases,'the'membrane'potential'of'cell'will'(hyperpolarize/depolarize/not)change).'

' 5.'One'fateful'day,'a'scientist'accidentally'falls'into'a'vat'of'radioactive'waste'and'acquires'exactly)one)genetic) mutation)expressed'only'in'his'neurons.'As'his'peer'and'friend,'you'decide'to'help'figure'out'exactly'what' went'wrong.'When'you'depolarize'one'of'his'mutant'neurons,'you'observe'the'resting'membrane'potential'is' unchanged'but'that'the'mutant'action'potential'looks'very'different'from'a'normal'action'potential'(see' diagram'below).''

+ +'

a.'%Could'this'mutant'action'potential'be'caused'by'a'defect'in'the'Na /K pump?'Explain'(1-2' sentences). '' No'because'the'pump'is'important'for'setting'resting'Vm;'however,'rest'is'unchanged'in'the'mutant'neuron.'' b.'Could'this'mutant'action'potential'be'caused'by'a'mutation'in'the'leak'channels?'Explain'(1-2' sentences). '' No,'for'the'same'reason'as'in'part'(a) ' '

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