Refractory period (physiology) - Wikipedia

In physiology, a refractory period is a period of time during which an organ or cell is incapable of repeating a particular action, or (more precisely) the ... Refractoryperiod(physiology) FromWikipedia,thefreeencyclopedia Jumptonavigation Jumptosearch Periodoftimeafteranorganismperformsanactionbeforeitispossibletoperformagain Thisarticleisaboutrefractoryperiodsinphysiology.Forsexualrefractoryperiods,seerefractoryperiod(sex). Thisarticleneedsadditionalcitationsforverification.Pleasehelpimprovethisarticlebyaddingcitationstoreliablesources.Unsourcedmaterialmaybechallengedandremoved.Findsources: "Refractoryperiod" physiology – news ·newspapers ·books ·scholar ·JSTOR(April2013)(Learnhowandwhentoremovethistemplatemessage) Refractorinessisthefundamentalpropertyofanyobjectofautowavenature(especiallyexcitablemedium)nottorespondonstimuli,iftheobjectstaysinthespecificrefractorystate.Incommonsense,refractoryperiodisthecharacteristicrecoverytime,aperiodthatisassociatedwiththemotionoftheimagepointontheleftbranchoftheisocline u ˙ = 0 {\displaystyle{\dot{u}}=0} [B:1](formoredetails,seealsoReaction–diffusionandParabolicpartialdifferentialequation). Schematicofanelectrophysiologicalrecordingofanactionpotentialshowingthevariousphasesthatoccurasthewavepassesapointonacellmembrane. Inphysiology,[B:2]arefractoryperiodisaperiodoftimeduringwhichanorganorcellisincapableofrepeatingaparticularaction,or(moreprecisely)theamountoftimeittakesforanexcitablemembranetobereadyforasecondstimulusonceitreturnstoitsrestingstatefollowinganexcitation.Itmostcommonlyreferstoelectricallyexcitablemusclecellsorneurons.Absoluterefractoryperiodcorrespondstodepolarizationandrepolarization,whereasrelativerefractoryperiodcorrespondstohyperpolarization. Contents 1Electrochemicalusage 2Cardiacrefractoryperiod 3Neuronalrefractoryperiod 4Skeletalmusclerefractoryperiod 5Seealso 6References Electrochemicalusage[edit] Seealso:Actionpotential Afterinitiationofanactionpotential,therefractoryperiodisdefinedtwoways: Theabsoluterefractoryperiodcoincideswithnearlytheentiredurationoftheactionpotential.Inneurons,itiscausedbytheinactivationoftheNa+channelsthatoriginallyopenedtodepolarizethemembrane.Thesechannelsremaininactivateduntilthemembranehyperpolarizes.Thechannelsthenclose,de-inactivate,andregaintheirabilitytoopeninresponsetostimulus. Therelativerefractoryperiodimmediatelyfollowstheabsolute.Asvoltage-gatedpotassiumchannelsopentoterminatetheactionpotentialbyrepolarizingthemembrane,thepotassiumconductanceofthemembraneincreasesdramatically.K+ionsmovingoutofthecellbringthemembranepotentialclosertotheequilibriumpotentialforpotassium.Thiscausesbriefhyperpolarizationofthemembrane,thatis,themembranepotentialbecomestransientlymorenegativethanthenormalrestingpotential.Untilthepotassiumconductancereturnstotherestingvalue,agreaterstimuluswillberequiredtoreachtheinitiationthresholdforaseconddepolarization.Thereturntotheequilibriumrestingpotentialmarkstheendoftherelativerefractoryperiod. Cardiacrefractoryperiod[edit] Mainarticle:Cardiac_action_potential§ Refractory_period EffectiveRefractoryPeriod Therefractoryperiodincardiacphysiologyisrelatedtotheioncurrentsthat,incardiaccellsasinnervecells,flowintoandoutofthecellfreely.Theflowofionstranslatesintoachangeinthevoltageoftheinsideofthecellrelativetotheextracellularspace.Asinnervecells,thischaracteristicchangeinvoltageisreferredtoasanactionpotential.Unlikethatinnervecells,thecardiacactionpotentialdurationiscloserto100ms(withvariationsdependingoncelltype,autonomictone,etc.).Afteranactionpotentialinitiates,thecardiaccellisunabletoinitiateanotheractionpotentialforsomedurationoftime(whichisslightlyshorterthanthe"true"actionpotentialduration).Thisperiodoftimeisreferredtoastherefractoryperiod,whichis250msindurationandhelpstoprotecttheheart. Intheclassicalsense,thecardiacrefractoryperiodisseparatedintoanabsoluterefractoryperiodandarelativerefractoryperiod.Duringtheabsoluterefractoryperiod,anewactionpotentialcannotbeelicited.Duringtherelativerefractoryperiod,anewactionpotentialcanbeelicitedunderthecorrectcircumstances. Thecardiacrefractoryperiodcanresultindifferentformsofre-entry,whichareacauseoftachycardia.[1][B:3]Vorticesofexcitationinthemyocardium(autowavevortices)areaformofre-entry.Suchvorticescanbeamechanismoflife-threateningcardiacarrhythmias.Inparticular,theautowavereverberator,morecommonlyreferredtoasspiralwavesorrotors,canbefoundwithintheatriaandmaybeacauseofatrialfibrillation. Neuronalrefractoryperiod[edit] Therefractoryperiodinaneuronoccursafteranactionpotentialandgenerallylastsonemillisecond.Anactionpotentialconsistsofthreephases. Phaseoneisdepolarization.Duringdepolarization,voltage-gatedsodiumionchannelsopen,increasingtheneuron'smembraneconductanceforsodiumionsanddepolarizingthecell'smembranepotential(fromtypically-70mVtowardapositivepotential).Inotherwords,themembraneismadelessnegative.Afterthepotentialreachestheactivationthreshold(-55mV),thedepolarizationisactivelydrivenbytheneuronandovershootstheequilibriumpotentialofanactivatedmembrane(+30mV). Phasetwoisrepolarization.Duringrepolarization,voltage-gatedsodiumionchannelsinactivate(differentfromtheclosedstate)duetothenow-depolarizedmembrane,andvoltage-gatedpotassiumchannelsactivate(open).Boththeinactivationofthesodiumionchannelsandtheopeningofthepotassiumionchannelsacttorepolarizethecell'smembranepotentialbacktoitsrestingmembranepotential. Whenthecell'smembranevoltageovershootsitsrestingmembranepotential(near-60mV),thecellentersaphaseofhyperpolarization.Thisisduetoalarger-than-restingpotassiumconductanceacrossthecellmembrane.Thispotassiumconductanceeventuallydropsandthecellreturnstoitsrestingmembranepotential. Recentresearchhasshownthatneuronalrefractoryperiodscanexceed20milliseconds.Furthermore,therelationbetweenhyperpolarizationandtheneuronalrefractorywasquestioned,asneuronalrefractoryperiodswereobservedforneuronsthatdonotexhibithyperpolarization.[2][3]Theneuronalrefractoryperiodwasshowntobedependentontheoriginoftheinputsignaltotheneuron,aswellastheprecedingspikingactivityoftheneuron.[3] Therefractoryperiodsareduetotheinactivationpropertyofvoltage-gatedsodiumchannelsandthelagofpotassiumchannelsinclosing.Voltage-gatedsodiumchannelshavetwogatingmechanisms,theactivationmechanismthatopensthechannelwithdepolarizationandtheinactivationmechanismthatclosesthechannelwithrepolarization.Whilethechannelisintheinactivestate,itwillnotopeninresponsetodepolarization.Theperiodwhenthemajorityofsodiumchannelsremainintheinactivestateistheabsoluterefractoryperiod.Afterthisperiod,thereareenoughvoltage-activatedsodiumchannelsintheclosed(active)statetorespondtodepolarization.However,voltage-gatedpotassiumchannelsthatopenedinresponsetorepolarizationdonotcloseasquicklyasvoltage-gatedsodiumchannels;toreturntotheactiveclosedstate.Duringthistime,theextrapotassiumconductancemeansthatthemembraneisatahigherthresholdandwillrequireagreaterstimulustocauseactionpotentialstofire.Inotherwords,becausethemembranepotentialinsidetheaxonbecomesincreasinglynegativerelativetotheoutsideofthemembrane,astrongerstimuluswillberequiredtoreachthethresholdvoltage,andthus,initiateanotheractionpotential.Thisperiodistherelativerefractoryperiod. Skeletalmusclerefractoryperiod[edit] Themuscleactionpotentiallastsroughly2–4 msandtheabsoluterefractoryperiodisroughly1–3 ms,shorterthanothercells. Seealso[edit] Autowave Parabolicpartialdifferentialequation Reaction–diffusionsystem References[edit] Books ^Грехова,М.Т.,ed.(1981).Автоволновыепроцессывсистемахсдиффузией[Autowaveprocessesinsystemswithdiffusion](inRussian).Горький:ИнститутприкладнойматематикиАНСССР.p. 287. ^Schmidt,RobertF.;Thews,Gerhard(1983).Humanphysiology.Springer-Verlag.p. 725.ISBN 978-3540116691. ^Елькин,Ю.Е.;Москаленко,А.В.(2009)."Базовыемеханизмыаритмийсердца"[Basicmechanismsofcardiacarrhythmias].InArdashev,prof.A.V.(ed.).Клиническаяаритмология[Clinicalarrhythmology](inRussian).Moscow:MedPraktika.p. 1220.ISBN 978-5-98803-198-7. ^Wiener,N.;Rosenblueth,A.(July1946)."Themathematicalformulationoftheproblemofconductionofimpulsesinanetworkofconnectedexcitableelements,specificallyincardiacmuscle".ArchivosDelInstitutoDeCardiologiaDeMexico.16(3):205–265.ISSN 0020-3785.PMID 20245817. ^Sardi,Shira;Vardi,Roni;Tugendhaft,Yael;Sheinin,Anton;Goldental,Amir;Kanter,Ido(2022-01-03)."Longanisotropicabsoluterefractoryperiodswithrapidrisetimestoreliableresponsiveness".PhysicalReviewE.105(1):014401.doi:10.1103/PhysRevE.105.014401. ^abVardi,Roni;Tugendhaft,Yael;Sardi,Shira;Kanter,Ido(2021-06-01)."Significantanisotropicneuronalrefractoryperiodplasticity".EPL(EurophysicsLetters).134(6):60007.doi:10.1209/0295-5075/ac177a.ISSN 0295-5075. 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