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1、新東方在線[]網(wǎng)絡課堂電子教材系列GMAT閱讀講義1GMAT閱讀講義閱讀講義主講：王鵬主講：王鵬歡迎使用新東方在線電子教材歡迎使用新東方在線電子教材GMAT核心閱讀核心閱讀Passage1Caffeinethestimulantincoffeehasbeencalled“themostwidelyusedpsychoactivesubstanceonEarth.”SynderDalyBrunshaverecentlyproposedth
2、atcaffeineaffectsbehavibycounteringtheactivityin(5)thehumanbrainofanaturallyoccurringchemicalcalledadenosine.Adenosinenmallydepressesneuronfiringinmanyareasofthebrain.Itapparentlydoesthisbyinhibitingthereleaseofneurotran
3、smitterschemicalsthatcarrynerveimpulsesfromoneneurontothenext.(10)Likemanyotheragentsthataffectneuronfiringadenosinemustfirstbindtospecificreceptsonneuronalmembranes.Thereareatleasttwoclassesofthesereceptswhichhavebeende
4、signatedA1A2.Snyderetalproposethatcaffeinewhichisstruc(15)turallysimilartoadenosineisabletobindtobothtypesofreceptswhichpreventsadenosinefromattachingthereallowstheneuronstofiremereadilythantheyotherwisewould.Fmanyyearsc
5、affeine’seffectshavebeenattri(20)butedtoitsinhibitionoftheproductionofphosphodiesteraseanenzymethatbreaksdownthechemicalcalledcyclicAMP.AnumberofneurotransmittersexerttheireffectsbyfirstincreasingcyclicAMPconcentrationsi
6、ntargetneurons.Therefeprolongedperiodsat(25)theelevatedconcentrationsasmightbebroughtaboutbyaphosphodiesteraseinhibitcouldleadtoagreater新東方在線[]網(wǎng)絡課堂電子教材系列GMAT閱讀講義3(C)increasescyclicAMPconcentrationsintargetneuronswhereasa
7、denosinedecreasessuchconcentrations(D)permitsreleaseofneurotransmitterswhenitisboundtoadenosinereceptswhereasadenosineinhibitssuchrelease(E)inhibitsbothneuronfiringtheproductionofphosphodiesterasewhenthereisasufficientco
8、ncentrationinthebrainwhereasadenosineinhibitsonlyneuronfiring3.InresponsetoexperimentalresultsconcerningIBMXSnyderetalcontendedthatitisnotuncommonfpsychoactivedrugstohave(A)mixedeffectsinthebrain(B)inhibityeffectsonenzym
9、esinthebrain(C)closestructuralrelationshipswithcaffeine(D)depressiveeffectsonmouselocomotion(E)theabilitytodislodgecaffeinefromreceptsinthebrain4.AccdingtoSnyderetalallofthefollowingcompoundscanbindtospecificreceptsinthe
10、brainEXCEPT(A)IBMX(B)caffeine(C)adenosine(D)theophylline(E)phosphodiesterase5.Snyderetalsuggestthatcaffeine’sabilitytobindtoA1A2receptscanbeatleastpartiallyattributedtowhichofthefollowing(A)Thechemicalrelationshipbetween
11、caffeinephosphodiesterase(B)Thestructuralrelationshipbetweencaffeineadenosine(C)Thestructuralsimilaritybetweencaffeineneurotransmitters(D)Theabilityofcaffeinetostimulatebehavi(E)Thenaturaloccurrenceofcaffeineadenosineint
12、hebrain6.TheauthquotesSnyderetalinlines3843mostprobablyinderto(A)revealsomeoftheassumptionsunderlyingtheirthey(B)summarizeamajfindingoftheirexperiments(C)pointoutthattheirexperimentswerelimitedtothemouse(D)indicatethatth
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