【精品】powerpoint 演示文稿山东大学医学院生理学研究所96.ppt

1,liuchuanyong刘传勇instituteofphysiologymedicalschoolofsdutel88381175(lab)88382098(office)email:liucywebsite:,2,section2,bioelectricalphenomenaofthecell,3,basicconcepts,voltachargedifferencebetweentwopointsinspace,4,basicconcepts,ionschargedparticlesanionsnegativelychargedparticlescationspositivelychargedparticles,5,basicconceptsforcesthatdetermineionicmovement,electrostaticforcesoppositechargesattractidenticalchargesrepelconcentrationforcesdiffusionmovementofionsthroughsemipermeablemembraneosmosismovementofwaterfromregionofhighconcentrationtolow,6,selectivepermeabilityofmembranes,someionspermittedtocrossmoreeasilythanothersneuronalmembranescontainionchannelsproteintubesthatspanthemembranesomestayopenallthetime(nongated)someopenontheoccasionofanactionpotential,causingachangeinthepermeabilityofthemembrane(gated),7,i.membranerestingpotential,aconstantpotentialdifferenceacrosstherestingcellmembranecellsabilitytofireanactionpotentialisduetothecellsabilitytomaintainthecellularrestingpotentialatapproximately70mv(-.07volt)thebasicsignalingpropertiesofneuronsaredeterminedbychangesintherestingpotential,8,membranerestingpotential,everyneuronhasaseparationofelectricalchargeacrossitscellmembrane.themembranepotentialresultsfromaseparationofpositiveandnegativechargesacrossthecellmembrane.,9,membranerestingpotential,excessofpositivechargesoutsideandnegativechargesinsidethemembranemaintainedbecausethelipidbilayeractsasabarriertothediffusionofions,givesrisetoanelectricalpotentialdifference,whichrangesfromabout60to70mv.(microelectrode),10,conceptofrestingpotential(rp),apotentialdifferenceacrossthecellmembraneatthereststageorwhenthecellisnotstimulated.property:itisconstantorstableitisnegativeinsiderelativetotheoutsiderestingpotentialsaredifferentindifferentcells.,11,ionchannels,twotypesofionchannelsgatednon-gated,12,restingmembranepotential,na+andcl-aremoreconcentratedoutsidethecellk+andorganicanions(organicacidsandproteins)aremoreconcentratedinside.,13,intracellularvsextracellularionconcentrations,ionintracellularextracellularna+5-15mm145mmk+140mm5mmmg2+0.5mm1-2mmca2+10-7mm1-2mmh+10-7.2m(ph7.2)10-7.4m(ph7.4)cl-5-15mm110mm,14,restingmembranepotential,potassiumions,concentratedinsidethecelltendtomoveoutwarddowntheirconcentrationgradientthroughnongatedpotassiumchannelsbuttherelativeexcessofnegativechargeinsidethemembranetendtopushpotassiumionsoutofthecell,15,potassiumequilibrium,-90mv,16,restingmembranepotential,butwhataboutsodium?electrostaticandchemicalforcesacttogetheronna+ionstodrivethemintothecellthena+channelcloseduringtherestingstate,na+ismoreconcentratedoutsidethaninsideandthereforetendstoflowintothecelldownitsconcentrationgradient,na+isdrivenintothecellbytheelectricalpotentialdifferenceacrossthemembrane.,17,na+electrochemicalgradient,18,equilibriumpotentials,theoreticalvoltageproducedacrossthemembraneifonly1ioncoulddiffusethroughthemembrane.ifmembraneonlypermeabletok+,k+diffusesuntilk+isatequilibrium.forceofelectricalattractionanddiffusionare=opposite.,19,calculatingequilibriumpotentialnernstequation,allowstheoreticalmembranepotentialtobecalculatedforparticularion.membranepotentialthatwouldexactlybalancethediffusiongradientandpreventthenetmovementofaparticularion.valuedependsontheratioofiononthe2sidesofthemembrane.,20,where,coandci=extraandintracellularionr=universalgasconstant(8.3joules.k-1.mol-1)t=absolutetemperature(k)f=faradayconstant(96,500coulombs.mol-1)z=chargeofion(na+=+1,ca2+=+2,cl-=-1),fork+,withk+o=4mmol.l-1andk+i=150mmol.l-1at37c,ek=-97mvena=+60mv,21,k+o=4mmol.l-1,22,restingmembranepotential,restingmembranepotentialislessthanekbecausesomena+canalsoenterthecell.theslowrateofna+influxisaccompaniedbyslowrateofk+outflux.dependsupon2factors:ratiooftheconcentrationsofeachiononthe2sidesoftheplasmamembrane.specificpermeabilityofmembranetoeachdifferention.restingmembranepotentialofmostcellsrangesfrom-65to85mv.,23,thesodium-potassiumpump,dissipationofionicgradientsisultimatelypreventedbyna+-k+pumps,extrudesna+fromthecellwhiletakingink,24,restingpotential,25,theformationofrestingpotentialdependson:,concentrationdifferenceofk+acrossthemembranepermeabilityofna+andk+duringtherestingstatena+-k+pump,26,factorsthataffectrestingpotential,differenceofk+ionconcentrationacrossthemembranepermeabilityofthemembranetona+andk+.actionofna+pump,27,basicelectrophysiologicaltermsi:,polarization:astateinwhichmembraneispolarizedatrest,negativeinsideandpositiveoutside.depolarization:themembranepotentialbecomeslessnegativethantherestingpotential(closetozero).hyperpolarization:themembranepotentialismorenegativethantherestinglevel.,28,basicelectrophysiologicaltermsi:,reverspolarization:areversalofmembranepotentialpolarity.theinsideofacellbecomespositiverelativetotheoutside.repolarization:restorationofnormalpolarizationstateofmembrane.aprocessinwhichthemembranepotentialreturnstowardfromdepolarizedleveltothenormalrestingmembranevalue.,29,iiactionpotential,successivestages:restingstagedepolarizationstagerepolarizationstageafter-potentialstage,(1),(2),(3),(4),30,concept,actionpotentialisarapid,reversible,andconductivechangeofthemembranepotentialafterthecellisstimulated.nervesignalsaretransmittedbyactionpotentials.,31,actionpotentialsequence,voltage-gatedna+channelsopenandna+rushesintothecell,32,actionpotentialsequence,atabout+30mv,sodiumchannelsclose,butnow,voltage-gatedpotassiumchannelsopen,causinganoutflowofpotassium,downitselectrochemicalgradient,33,actionpotentialsequence,equilibriumpotentialofthecellisrestored,34,actionpotentialsequence,thesodiumpotassiumpumpislefttocleanupthemess,35,ionpermeabilityduringtheap,figure8-12:refractoryperiods,36,basicelectrophysiologicaltermsii(1),excitability:theabilityofthecelltogeneratetheactionpotentialexcitablecells:cellsthatgenerateactionpotentialduringexcitation.inexcitablecells(muscle,nerve,secreterycells),theactionpotentialisthemarkerofexcitation.somescholarsevensuggestthatinexcitablecells,actionpotentialisidenticaltotheexcitation.,37,basicelectrophysiologicaltermsii(2),stimulus:asuddenchangeofthe(internalorexternal)environmentalconditionofthecell.includesphysicalandchemicalstimulus.theelectricalstimulusisoftenusedforthephysiologicalresearch.threshold(intensity):thelowestorminimalintensityofstimulustoelicitanactionpotential(threefactorsofthestimulation:intensity,duration,rateofintensitychange),38,basicelectrophysiologicaltermsii(3),typesofstimulus:thresholdstimulus:thestimuluswiththeintensityequaltothresholdsubthresholdstimulus:thestimuluswiththeintensityweakerthanthethresholdsuprathresholdstimulus:thestimuluswiththeintensitygreaterthanthethreshold.,39,actionpotentialsummary,reductioninmembranepotential(depolarization)tothresholdlevelleadstoopeningofna+channels,allowingna+toenterthecellinteriorbecomespositivethena+channelsthencloseautomaticallyfollowedbyaperiodofinactivation.k+channelsopen,k+leavesthecellandtheinterioragainbecomesnegative.processlastsabout1/1000thofasecond.,40,propertiesoftheactionpotential,“allornone”phenomenonathresholdorsuprathresholdstimulusappliedtoasinglenervefiberalwaysinitiatethesameactionpotentialwithconstantamplitude,timecourseandpropagationvelocity.propagationtransmittedinbothdirectioninanervefiber,41,iiiinitiationofactionpotential,42,squidgiantaxon,43,gatedchannelstates,44,na+channela1-subunitstructure,i,ii,iii,iv,-inactivation“gate”,ivs4voltagesensor,45,voltagegated,but“ready”,not“ready”,46,activation&fastinactivation,47,sodiumactivationandinactivationvariablevsvoltage,activationgate,inactivationgate,ifrestingpotentialdepolarizedby1520mv,thenactivationgateopenedwith5000 xincreaseinna+permeabilityfollowedbyinactivationgateclose1mslater,48,positivefeedbackloop,na+enters(depolarization),v-gatena+channelsopen,stimulation,49,actionpotentialinitiation,s.i.z.,50,actionpotentialtermination,51,52,thresholdpotential,thresholdpotentialplaysakeyroleinthegenesisofactionpotential.thresholdpotentialisacriticalmembranepotentiallevelatwhichanactionpotentialcanoccur.whycanallthena+channelopenatthethresholdpotential?itisdependentonthegatingpropertyofthevoltage-gatedna+channels.thevalueofthresholdpotentialofmostexcitablecellmembraneisabout15to20mvlessnegativethantherestingpotential.thethresholdstimulusisjuststrongenoughtodepolarizethemembranetothethresholdpotentiallevel,thereforeitcancauseanactionpotential.,53,electrophysiologicalmethodtorecordmembranepotentiali,voltageclamp,54,55,coleandcolleaguesdevelopedamethodformaintainingvmatanydesiredvoltagelevel(fba,feedbackamplifier)requiredmonitoringvoltagechanges,feedingitthroughanamplifiertodrivecurrentintooroutofthecelltodynamicallymaintainthevoltagewhilerecordingthecurrentrequiredtodoso,thevoltageclamp,56,thehodgkin-huxleymodelofactionpotentialgeneration,57,58,triphasicresponse,59,evidenceforasodiumcurrent,removeextracellularsodium,60,modernproofofnatureofcurrents,useionselectiveagents,61,removingna+fromthebathingmedium,inabecomesnegligiblesoikcanbemeasureddirectly.subtractingthiscurrentfromthetotalcurrentyieldedina.,62,63,conductanceofna+andk+channels,64,voltage-dependenceofconductance,65,anactionpotential,gnaincreasesquickly,buttheninactivationkicksinanditdecreasesagain.gkincreasesmoreslowly,andonlydecreasesoncethevoltagehasdecreased.thena+currentisautocatalytic.anincreaseinvincreasesgna,whichincreasesthena+current,andincreasesv,etc.hence,thethresholdforactionpotentialinitiationiswheretheinwardna+currentexactlybalancestheoutwardk+current.,66,67,cytoplasm,ionchannels,giga-seal,glass,microelectrode,suction,1m,patchclamprecording,cellmembrane,68,69,100ms,4pa,closed,open,singlechannelrecord,70,oneresultfrompatchclampstudieswasthefindingthationchannelsconductcurrentsinanallornothingfashion,71,voltage-dependentchannelconductance,72,howchannelconductancesaccumulate,nextpageshowsanidealizedversion,73,74,inactivatingna+channelcurrents,75,ivlocalresponse,76,graded(local)potentialchanges,2xmorechemical=2xmorepotentialchange,77,localresponse,definition:localresponseisasmallchangeinmembranepotentialcausedbyasubthresholdstimulusproperties:itsagradedpotentialitspropagationiselectronicconductionitcanbesummedbytwowaysspatialsummationtemporalsummation,78,excitatory,excitatory,inhibitory,time,membranepotential(mv),spatialsummation,spatialsummation,a,b,c,d,a,b,c,d,79,excitatory,excitatory,inhibitory,time,membranepotential(mv),temporal&spatialsummation,temporalsummation,a,b,c,d,a,b,c,d,80,distributionofchannels,leakchannelseverywhere,axonhillock(triggerzone),81,roleofthelocalpotential,facilitatethecell.thismeansitincreas