Stages of Sleep: What Happens in a Sleep Cycle

There are four sleep stages3; one for rapid eye movement (REM) sleep and three that form non-REM (NREM) sleep. These stages are determined based ... Opensinanewwindow Share: Home /StagesofSleep StagesofSleep UpdatedAugust10,2022 Writtenby EricSuni,StaffWriter MedicallyReviewedby Dr.NilongVyas,Pediatrician FactChecked Ourteamofwriters,editors,andmedicalexpertsrigorouslyevaluateseacharticletoensuretheinformationisaccurateandexclusivelycitesreputablesources.LearnMore Weregularlyassesshowthecontentinthisarticlealignswithcurrentscientificliteratureandexpertrecommendationsinordertoprovidethemostup-to-dateresearch. Whenthinkingaboutgettingthesleepyouneed,it’snormaltofocusonhowmanyhoursofsleepyouget.Whilesleepdurationisundoubtedlyimportant,it’snottheonlypartoftheequation. It’salsocriticaltothinkaboutsleepqualityandwhetherthetimespentsleepingisactuallyrestorative.Progressingsmoothlymultipletimesthroughthesleepcycle,composedoffourseparatesleepstages,isavitalpartofgettingtrulyhigh-qualityrest. Eachsleepstageplaysapartinallowingyourmindandbodytowakeuprefreshed.Understandingthesleepcyclealsohelpsexplainhowcertainsleepdisorders,includinginsomniaandobstructivesleepapneacanimpactaperson’ssleepandhealth. WhatIstheSleepCycle?     Sleepisnotuniform.Instead,overthecourseofthenight,yourtotalsleepismadeupofseveralroundsofthesleepcycle,whichiscomposedoffourindividualstages.Inatypicalnight,apersongoesthroughfourtosixsleepcycles.Notallsleepcyclesarethesamelength,butonaveragetheylastabout90minuteseach. AreAllSleepCyclestheSame? Itisnormalforsleepcyclestochangeasyouprogressthroughyournightlysleep.Thefirstsleepcycleisoftentheshortest,rangingfrom70-100minutes,whilelatercyclestendtofallbetween90and120minutes.Inaddition,thecompositionofeachcycle—howmuchtimeisspentineachsleepstage—changesasthenightgoesalong. Sleepcyclescanvaryfrompersontopersonandfromnighttonightbasedonawiderangeoffactorssuchasage,recentsleeppatterns,andalcoholconsumption. WhatAretheSleepStages? Therearefoursleepstages;oneforrapideyemovement(REM)sleepandthreethatformnon-REM(NREM)sleep.Thesestagesaredeterminedbasedonananalysisofbrainactivityduringsleep,whichshowsdistinctpatternsthatcharacterizeeachstage. SleepStages TypeofSleep OtherNames NormalLength Stage1 NREM N1 1-5minutes Stage2 NREM N2 10-60minutes Stage3 NREM N3,Slow-WaveSleep(SWS),DeltaSleep,DeepSleep 20-40minutes Stage4 REM REMSleep 10-60minutes Thebreakdownofaperson’ssleepintovariouscyclesandstagesiscommonlyreferredtoassleeparchitecture.Ifsomeonehasasleepstudy,thissleeparchitecturecanberepresentedvisuallyinahypnogram. Theclassificationofsleepstageswasupdatedin2007bytheAmericanAcademyofSleepMedicine(AASM).Beforethat,mostexpertsreferredtofivesleepstages,buttoday,theAASMdefinitionsofthefourstagesrepresenttheconsensusunderstandingofthesleepcycle.   NREMSleepPatterns NREMsleepiscomposedofthreedifferentstages.ThehigherthestageofNREMsleep,theharderitistowakeapersonupfromtheirslumber. Stage1/N1 Stage1isessentiallythe“dozingoff”stage,anditnormallylastsjustonetofiveminutes. DuringN1sleep,thebodyhasn’tfullyrelaxed,thoughthebodyandbrainactivitiesstarttoslowwithperiodsofbriefmovements(twitches).Therearelightchangesinbrainactivityassociatedwithfallingasleepinthisstage. It’seasytowakesomeoneupduringthissleepstage,butifapersonisn’tdisturbed,theycanmovequicklyintostage2.Asthenightunfolds,anuninterruptedsleepermaynotspendmuchmoretimeinstage1astheymovethroughfurthersleepcycles. Stage2/N2 Duringstage2,thebodyentersamoresubduedstateincludingadropintemperature,relaxedmuscles,andslowedbreathingandheartrate.Atthesametime,brainwavesshowanewpatternandeyemovementstops.Onthewhole,brainactivityslows,butthereareshortburstsofactivitythatactuallyhelpresistbeingwokenupbyexternalstimuli. Stage2sleepcanlastfor10-25minutesduringthefirstsleepcycle,andeachN2stagecanbecomelongerduringthenight.Collectively,apersontypicallyspendsabouthalftheirsleeptimeinN2sleep. Stage3/N3 Stage3sleepisalsoknownasdeepsleep,anditishardertowakesomeoneupiftheyareinthisphase.Muscletone,pulse,andbreathingratedecreaseinN3sleepasthebodyrelaxesevenfurther. Thebrainactivityduringthisperiodhasanidentifiablepatternofwhatareknownasdeltawaves.Forthisreason,stage3mayalsobecalleddeltasleeporslow-wavesleep(SWS). Expertsbelievethatthisstageiscriticaltorestorativesleep,allowingforbodilyrecoveryandgrowth.Itmayalsobolstertheimmunesystemandotherkeybodilyprocesses.Eventhoughbrainactivityisreduced,thereisevidencethatdeepsleepcontributestoinsightfulthinking,creativity,andmemory. Wespendthemosttimeindeepsleepduringthefirsthalfofthenight.Duringtheearlysleepcycles,N3stagescommonlylastfor20-40minutes.Asyoucontinuesleeping,thesestagesgetshorter,andmoretimegetsspentinREMsleepinstead. REMSleepPatterns DuringREMsleep,brainactivitypicksup,nearinglevelsseenwhenyou’reawake.Atthesametime,thebodyexperiencesatonia,whichisatemporaryparalysisofthemuscles,withtwoexceptions:theeyesandthemusclesthatcontrolbreathing.Eventhoughtheeyesareclosed,theycanbeseenmovingquickly,whichishowthisstagegetsitsname. REMsleepisbelievedtobeessentialtocognitivefunctionslikememory,learning,andcreativity.REMsleepisknownforthemostvividdreams,whichisexplainedbythesignificantuptickinbrainactivity.Dreamscanoccurinanysleepstage,buttheyarelesscommonandintenseintheNREMperiods. Undernormalcircumstances,youdon’tenteraREMsleepstageuntilyou’vebeenasleepforabout90minutes.Asthenightgoeson,REMstagesgetlonger,especiallyinthesecondhalfofthenight.WhilethefirstREMstagemaylastonlyafewminutes,laterstagescanlastforaroundanhour.Intotal,REMstagesmakeuparound25%ofsleepinadults. WhyDotheSleepStagesMatter? Sleepstagesareimportantbecausetheyallowthebrainandbodytorecuperateanddevelop.FailuretoobtainenoughofbothdeepsleepandREMsleepmayexplainsomeoftheprofoundconsequencesofinsufficientsleeponthinking,emotions,andphysicalhealth. Sleeperswhoarefrequentlyawokenduringearlierstages,suchaspeoplewithsleepapnea,maystruggletoproperlycycleintothesedeepersleepstages.Peoplewithinsomniamaynotgetenoughtotalsleeptoaccumulatetheneededtimeineachstage. WhatAffectsSleepStages? Whilethereisatypicalpatternforsleepstages,therecanbesubstantialindividualvariationbasedonanumberoffactors: Age:Timeineachstagechangesdramaticallyoveraperson’slife.Newbornsspendfarmoretime(around50%)inREMsleepandmayenteraREMstageassoonastheyfallasleep.Astheygetolder,theirsleepbecomessimilartothatofadults,normallyreachingacomparablesleeparchitecturebytheageof5.Ontheotherhand,elderlypeopletendtospendlesstimeinREMsleep. Recentsleeppatterns:Ifapersongetsirregularorinsufficientsleepoveraperiodofdaysormore,itcancauseanabnormalsleepcycle. Alcohol:Alcoholandsomeotherdrugscanaltersleeparchitecture.Forexample,alcoholdecreasesREMsleepearlyinthenight,butasthealcoholwearsoff,thereisaREMsleeprebound,withprolongedREMstages. Sleepdisorders:Sleepapnea,RestlessLegSyndrome(RLS),andotherconditionsthatcausemultipleawakeningsmayinterruptahealthysleepcycle. HowCanYouHaveaHealthierSleepCycle? Whileyoudon’thavefullcontrolofyoursleepcycle,youcantakestepstoimproveyourchancesofhavingahealthyprogressionthrougheachsleepstage. Akeystepistofocusonimprovingyoursleephygiene,whichreferstoyoursleepenvironment(thebestmattress,bestpillows,orsheets,etc.)andsleep-relatedhabits.Achievingamoreconsistentsleepschedule,gettingnaturaldaylightexposure,avoidingalcoholbeforebedtime,andeliminatingnoiseandlightdisruptionscanhelpyougetuninterruptedsleepandpromoteproperalignmentofyourcircadianrhythm. Ifyoufindthatyouhaveexcessivedaytimesleepinessorotherwisesuspectthatyoumighthaveasleepdisorderlikesleepapnea,it’simportanttotalkwithadoctorwhocanmostappropriatelyguideyourcare.Addressingunderlyingissuesmaypavethewayformorecompleteandrestorativesleepcycles. Wasthisarticlehelpful? YesNo AboutOurEditorialTeam EricSuni StaffWriter EricSunihasoveradecadeofexperienceasasciencewriterandwaspreviouslyaninformationspecialistfortheNationalCancerInstitute. Dr.NilongVyas Pediatrician MD Dr.VyasisapediatricianandfounderofSleeplessinNOLA.Shespecializesinhelpingparentsestablishhealthysleephabitsforchildren. Share: References +11 Sources 1. Patel,A.K.,Reddy,V.,&Araujo,J.F.(2020,April).Physiology,SleepStages.StatPearlsPublishing.Retrievedfrom https://www.ncbi.nlm.nih.gov/books/NBK526132/ 2. DivisionofSleepMedicineatHarvardMedicalSchool.(2007,December18).NaturalPatternsofSleep.RetrievedJuly28,2020,from http://healthysleep.med.harvard.edu/healthy/science/what/sleep-patterns-rem-nrem 3. 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Drago,V.,Foster,P.S.,Heilman,K.M.,Aricò,D.,Williamson,J.,Montagna,P.,&Ferri,R.(2011).Cyclicalternatingpatterninsleepanditsrelationshiptocreativity.Sleepmedicine,12(4),361–366. https://doi.org/10.1016/j.sleep.2010.11.009 8. DivisionofSleepMedicineatHarvardMedicalSchool.(2007,December18).Sleep,Learning,andMemory.RetrievedJuly28,2020,from http://healthysleep.med.harvard.edu/healthy/matters/benefits-of-sleep/learning-memory 9. Cai,D.J.,Mednick,S.A.,Harrison,E.M.,Kanady,J.C.,&Mednick,S.C.(2009).REM,notincubation,improvescreativitybyprimingassociativenetworks.ProceedingsoftheNationalAcademyofSciencesoftheUnitedStatesofAmerica,106(25),10130–10134. https://doi.org/10.1073/pnas.0900271106 10. MaquetP.(2000).Sleeponit!.Natureneuroscience,3(12),1235–1236. https://doi.org/10.1038/81750 11. Crosby,B.,LeBourgeois,M.K.,&Harsh,J.(2005).Racialdifferencesinreportednappingandnocturnalsleepin2-to8-year-oldchildren.Pediatrics,115(1Suppl),225–232. https://pubmed.ncbi.nlm.nih.gov/15866856/ LearnmoreabouttheStagesofSleep DeepSleep By DaniellePacheco | March11,2022 WhatisREMSleepandHowMuchDoYouNeed? By JaySummer | April26,2022 WhatisNREMSleep? By DaniellePacheco | July8,2022 5WaystoGetMoreREMSleep By DanielNoyed | March11,2022 ParadoxicalSleep By RobNewsom | March25,2022 OtherArticlesofInterest SleepHygiene TipsforBetterSleep WhatisSleepHygiene? HowtoRelieveStressatBedtime HowtoImproveSleepQuality HowMuchSleepDoYouNeed? BedroomEnvironment HowtoCreatetheIdealBedroomEnvironment HowLightAffectsSleep WhatisWhiteNoise? TechnologyintheBedroom HowDoesMusicAffectSleep? 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