大三上課件生理

Chapter4:Bioelectricity第四章：生物電Bioelectricityelectricpotentialsandcurrentsproducedbyoroccurringwithinlivingorganisms.Bioelectricpotentialsgenerallyrangeinstrengthfromonetoafewhundredmillivolts.Intheelectriceel,however,currentsofoneampereat600to1,000voltsaregenerated.Specialcells(derivedfrommodifiedmuscletissue)thatcanproduceelectricity(0.15Veach).Q:Whatisstaticelectricity?Electrocardiogram(ECG)心電圖Electroencephalogram(EEG)腦電圖Electromyogram(EMG)肌電圖Electroretinogram(ERG)視網(wǎng)膜電圖ClinicapplicationsElectricshock:brain(deepbrainstimulation),heartRecordingmethodphysiologyCellularmechanismRestingpotentialIntracellularrecordingMaintained?K+channelActionpotentialVoltageclampPropertyGenerated?Excitability?Spread?Na+channelK+channelLocalpotentialPatchclampPropertyGenerated?Spread?PropertyofthemembraneOutlineBasicelectricalpropertiesofcellmembranes

Conductanceisalsoameasurementofpermeability,orthequantityofopeningionchannels.Charge:Inbiologicalsystems,electricchargesareionsincludingcations(positive)andanions(negative),similarasinsaltsolution.IntracellularrecordingMaterials:the

squidgiant

axon(1mm?)Instruments:1.isosmoticsolution(等滲溶液)2.glasspipette/electrode(玻璃吸管/電極)3.voltagemeter4.referenceelectrodeProcedure:1.referenceelectrodeisplacedintheextracellularfluid2.Glassmicroelectrodeisimpaled

throughthecellmembranetotheinteriorofthecellResults:Voltagedecreasesfrom0to-90mV.AgPotential(mV)0-90RestingpotentialRestingpotentialistherelativelystaticmembranepotentialofquiescentcells,asopposedtothespecificdynamicelectrochemicalphenomenacalledactionpotentialandgraded(local)membranepotential.Insideofthecellisrelativelynegativetotheoutsideofthecell.CelltypesRestingpotential(mV)Skeletalmusclecells-95Smoothmusclecells-60Neurons-60to-70Astroglia-80to-90Photoreceptorcells-40Erythrocytes-9Createelectricfield:~2X105V/cm.(membranethickness:3-4nm.Anundetectablechangeinconcentrationofionscreatesagreatchangeonelectricpotential.)Affectvoltage-gatedchannels,andthepermeabilitytoions.IONCONCENTRATIONSINEXCITABLECELLS(mM)FROGMUSCLESQUIDAXONMammalianAXONINOUTINOUTINOUTNa+41255044010145K+1243400201405Ca++10-420.41010-42Cl-2781255605-30110SelectivelypermeabilityofmembraneThemembraneisimpermeabletobothNa+andK+.ThechannelsispermeabletoK+,butnotNa+Kdiffusedownitsconcentrationgradientfromcompartment2intocompartment1.Compartment1haveanexcessofpositivecharge,leavingbehindanexcessofnegativechargeincompartment2Createapotentialacrossthemembrane,whichprogressivelyincreasesandtendstoattractK+back

ReachequilibriumpotentialforK+(EK)Selectivelypermeabilityofaspecificionisrequiredforthemembranetoreachthision’sequilibriumpotential.EquilibriumpotentialEquilibriumpotentialofanionisthemembranepotentialatwhichthereisnonet(overall)flowofthatparticularionfromonesideofthemembranetotheother.Itisalsocalledreversalpotential.Thetwodrivingforcesforaniontocrossthemembraneareconcentrationgradient(Chemicalpotential)andthemembranepotential(Electricalpotential),thenetforceofthemistheelectrochemicalgradient.R:氣體常數(shù)T:絕對溫度Z:離子價F:法拉第常數(shù)electrochemicalgradient=0EquilibriumpotentialofthemainionsionsConcentrationinsidethemusclecell(mM)Concentrationoutsidethemusclecell(mM)ReversalPotential(mV)Na+12145+67K+1554-98Ca++10-42+125Cl-4120-90Themeasuredrestingmembranepotential(-90mVinmusclecell)isusuallysmallerthanthecalculateddiffusionpotentialofpotassiumionsonthetwosidesofthemembrane.TheeventsresponsibleforrestingpotentialGoldman-Hodgkin-Katz(GHK)EquationRestPK>>PNaREST:PK:PNa:PCl=1.0:0.04:0.45a.ContributionoftheK+diffusionthroughK+leakchannel(accordingtoNernstequation,-98mV)b.ContributionofNa+diffusionthroughNa+leakchannelcausing~10mVpositivityinside(-88mV,accordingtoGHKequation)c.ContributionoftheNa+-K+pump–electrogenicpumpwhichpumpsmoresodiumionoutthanpumpspotassiumionin.Thisleadsto2mVnegativityinside(-90mV).d.ECl-isequaltotherestingpotential,soCl-cannotchangetherestingpotential.e.PermeabilityofCa2+isverylow,soitcannotchangetherestingpotential.ContributionofothereventsexceptK+leakchannel1.Ionconcentrationdifferenceacrossthemembrane(mainlyK+)——generatedbyNa+-K+pump2.SelectivepermeabilityofcellmembranetoK+andalmostimpermeabletoNa+andCa2+3.K+diffusesthroughK+leakchannelandverylittleNa+diffusesthroughNa+leakchannel4.Whentheelectrochemicaldrivingforce=0,themembranepotentialisrestingpotential.5.Na+-K+pumpkeepsworkingtomaintainthegradientofK+andNa+,anditselectrogenicpropertycontributesverylittletotherestingpotentialdirectly.MechanismofRPformationSummary:Na+-K+pumpgeneratesandmaintainstheK+concentrationdifferenceacrossthemembrane,selectivepermeabilityofcellmembranetoK+setstherestingpotentialisveryclosetoEk.FactorsRestingpotential?[K+]o↑[K+]i↑PK↑PNa↑Na+-K+pumpactivity↑PCl↑PCa↑[Cl-]o↑R:氣體常數(shù)T:絕對溫度Z:離子價F:法拉第常數(shù)PhysiologicalimportanceofrestingpotentialThebasisforgenerationofAP.動作電位的基礎(chǔ)Determinetheexcitability