生理学

SectionIIBioelectricalPhenomenonandExcitability冯鉴强教授牛牛文库文档分享Electricalpotentialsexistacrossthemembranesofallcellsofthebody.“Excitablecellsortissues”forinstant:nerveandmusclecellscangeneraterapidlychangingelectrochemicalimpulsesatthemembranes.Othercells:glandularcells,macrophage,ciliatedcelletc.Localchangesinmembranepotentialsplaysignificantrolesincontrollingmanyofcell’sfunctions.Applicationofbioelectricalphenomenoninclinic:EEG(脑电图)，ECG(心电图)，EMG（肌电图）etc.Themethodformeasuringthemembranepotentialissimpleinthetheorybutoftendifficultinpracticeduetothesmallsizesofmostofthefiber.Figure2-9shows:牛牛文库文档分享Whenthe“indifferentelectrode”andrecordingelectrode(aglassmicroelectrodecontaininganelectrolytesolution)areputonthesurfaceofcellmembranes,nopotentialdifferenceisrecordedbetweentworecordingsites(thepotentialiszero).Whentherecordingelectrodepassesthroughthecellmembrane,thepotentialdecreasesrapidlyto-90millivoltsAttherestingcondition(thecellsorthenervefibersarenotstimulated),thepotentialdifferenceexistingbetweentheoutsideandinsideofthemembranesiscalledrestingmembranepotential.Extentoftherestingmembranepotential-10~100mVMeansthepotentialinsidethecellorthefiberis10to100millivoltsmorenegativethanthepotentialintheextracellularfluidontheoutsideofthecellorthefiber.牛牛文库文档分享Therestingmembranepotentialsofnervefiberandmusclecellofmammalianareabout-70~90mV.Polarization(极化)：thestateofrestingmembranepotentialthatis,negativepotentialexistsinsideofthemembrane,positivepotentialoutsideofthemembraneDepolarization(去极化或除极化)：negativepotentialvalueinsidethemembranedecreases(-70mV→-60mV)牛牛文库文档分享Hyperpolarization(超极化)：negativepotentialvalueinsidethemembraneincreases(-70mV→-90mV)Repolarization(复极化)：Afterdepolarization,thepotentialrecoversintherestingmembranepotentialdirection.(AP,动作电位)Whenthecellorthenervefiberisstimulatedbycertainintensityofelectricalstimuli,themembranepotentialhappensasuddenchangefromthenormalrestingnegativemembranepotentialtoapositivepotentialandthenendswithanalmostequallyrapidchangebacktothenegativepotential,thatistheactionpotential.牛牛文库文档分享Thepotentialrisesfrom-70~-90mVto+20~+40mV→thenlowersto-70~-90mV.Thesuccessivestagesoftheactionpotential:牛牛文库文档分享RestingstageThemembranetobe“polarized”(-70mV)DepolarizationstageThenormal“polarized”stateof-70mVrisingrapidlyinpositivedirection.牛牛文库文档分享Overshoot(超射)：Inlargenervefibers,themembranepotentialbeyondthezerolevelandbecomessomewhatpositive,butinsmallerfibersandmanycentralnervoussystemneurons,thepotentialmerelyapproachesthezerolevel,doesnotovershoot.Afterovershoot,themembranepotentialreturnsbacktothenormalnegativepotentialAfterpotential(后电位)1)depolarizingafterpotential(去极化后电位)ornegativeafterpotential2)hyperpolarizationafterpotential(超极化后电位)orpositivepotentialafterelicitedbythresholdstimuli,thesuperthresholdstimulusdoesnotincreasetheamplitudeofAPAPcantransfertosurroundingsiteThetransferringextentanddistanceofAParenotassociatedwiththestimulatingintensitythatcausesAP.Both1)and2)arecalledallornon（全或无）themechanismoforiginofrestingmembranepotential1902,Bersteinusesthe“membranetheory”toexplainthemechanismofthemembranepotentialkeypoint:1)concentrationdifferenceofK+ionexistsbetweentheoutsideandinsideofcellmembrane;2)atrestingstate,thecellmembraneonlyhaspermeabilitytoK+ion(钾平衡电位)静息时，细胞膜主要对K+有通透性；胞内K+浓度高于胞外K+浓度→K+从胞内流向胞外，使胞外正电荷增多→膜外正电位膜内负电位（静息电位）膜内带负电荷的蛋白分子不能流出胞外，使胞内负电荷增多；另外，K+外流使胞外正电荷增多，阻碍K+外流，当这两种因素完全抵消使K+外流的浓度差势能时，K+从胞内向胞外净移动停止，膜外正内负的状态稳定（K+平衡电位）牛牛文库文档分享NernstEquation(1889)Ek=RT/ZF*ln([K+]0/[K+]i)Ek=-87mV1944,HodgkinandKatzdemonstratedthatEkrecordedfromgiantaxonis-77mVnearto-87mVK+-Na+“leak”channel:throughwhichK+andNa+canleak.K+concentrationoutsidethemembraneK+↑→thepotential↓MembranepermeabilitytoK+andNa+morepermeabletoK+→thepotential↑morepermeabletoNa+→thepotential↓牛牛文库文档分享theactivitylevelofNa+-K+-pumpitisanelectrogenicpump膜受刺激而兴奋→膜对Na+通透性对K+的通透性（由于胞内外Na+浓度差及静息时胞内负电位）→Na+从胞外流入胞内→胞内负电位迅速消失→出现膜内正电位膜外负电位（锋电位）Na+equilibriumpotential流入的Na+↑→胞内正电荷↑→阻止Na+的进一步内移→Na+内流形成的正电位足以阻止Na+顺浓度差内流→Na+内流停止（Na+平衡电位）Voltaged-gateNa+channel:Ithastwogates:oneneartheoutsideofthechannelcalledtheactivationgate,anotherneartheinsidecalledtheinactivationgateThreeseparatestatesatrestingstate(-90mv),activationgateisclosed.牛牛文库文档分享Theactivatedstatewhenthepotentialbecomeslessneg