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1、BrainBasics:UnderstandingSleep:NationalInstituteofNeurologicalDisordersandStroke(NINDS)Page1of8BrainBasics:UnderstandingSleepDoyoueverfeelsleepyor"zoneout"duringtheday?DoyoufindithardtowakeuponMondaymornings?Ifso,youarefamiliarwiththepowerfulneedforsleep.Howev
2、er,youmaynotrealizethatsleepisasessentialforyourwell-beingasfoodandwater.òSleep:ADynamicActivityòHowMuchSleepDoWeNeed?òWhatDoesSleepDoForUs?òDreamingandREMSleepòSleepandCircadianRhythmsòSleepandDiseaseòSleepDisordersòTheFutureòTipsforaGoodNight'sSleepSleep:ADy
3、namicActivityUntilthe1950s,mostpeoplethoughtofsleepasapassive,dormantpartofourdailylives.Wenowknowthatourbrainsareveryactiveduringsleep.Moreover,sleepaffectsourdailyfunctioningandourphysicalandmentalhealthinmanywaysthatwearejustbeginningtounderstand.Nerve-sign
4、alingchemicalscalledneurotransmitterscontrolwhetherweareasleeporawakebyactingondifferentgroupsofnervecells,orneurons,inthebrain.Neuronsinthebrainstem,whichconnectsthebrainwiththespinalcord,produceneurotransmitterssuchasserotoninandnorepinephrinethatkeepsomepar
5、tsofthebrainactivewhileweareawake.Otherneuronsatthebaseofthebrainbeginsignalingwhenwefallasleep.Theseneuronsappearto"switchoff"thesignalsthatkeepusawake.Researchalsosuggeststhatachemicalcalledadenosinebuildsupinourbloodwhileweareawakeandcausesdrowsiness.Thisch
6、emicalgraduallybreaksdownwhilewesleep.Duringsleep,weusuallypassthroughfivephasesofsleep:stages1,2,3,4,andREM(rapideyemovement)sleep.Thesestagesprogressinacyclefromstage1toREMsleep,thenthecyclestartsoveragainwithstage1(seefigure1).Wespendalmost50percentofourtot
7、alsleeptimeinstage2sleep,about20percentinREMsleep,andtheremaining30percentintheotherstages.Infants,bycontrast,spendabouthalfoftheirsleeptimeinREMsleep.Duringstage1,whichislightsleep,wedriftinandoutofsleepandcanbeawakenedeasily.Oureyesmoveveryslowlyandmuscleact
8、ivityslows.Peopleawakenedfromstage1sleepoftenrememberfragmentedvisualimages.Manyalsoexperiencesuddenmusclecontractionscalledhypnicmyoclonia,oftenprecededbyasensationofstartingtofal
