11 lecture elevenstroke.docx
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11 lecture elevenstroke.docx
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11lectureelevenstroke
LectureEleven
Stroke
Scope:
Strokewillbeusedasaclinicalexampletoreviewinformationcovereduptothispointinthecourse.AstrokeoccurswhenthebloodsupplytoanareaoftheCNSiscompromisedeitherbyavesselbeingoccludedorruptured.Herewewillshowthatunderstandingthegrossorganizationofthebrainanditsbloodsupplyallowsforthepredictionofwhatfunctionswillbelostoraffectedafterastroke.Wewillalsoreviewdatafromstudiesimplicatingtheneurotransmitterglutamateasamajorplayerinstroke.
Outline
I.Thebrainisobviousveryactivemetabolically;itisestimatedthatalthoughthebrainaccountsforasmallportionofthetotalbodymass(1-2%),itreceivesabout20%oftherestingcardiacoutput.
A.Thebrainalsohasnoabilityorverylimitedabilitytostoreeitheroxygenorglucose.
B.Neuronsdiewithinminutesofbeingdeprivedofoxygen,andthusanythingthatinterfereswithbloodflowcancompromisebrainfunction,possiblypermanently.
II.StrokeisthethirdleadingcauseofdeathintheUnitedStatesandthenumberonecauseofdisability.
A.Astrokeisessentiallya“brainattack,”inthesensethatwethinkofcompromiseofcoronaryvesselsasbeinga“heartattack.”
B.Inordertounderstandstrokeandwhyparticularsigns(whatisfounduponexaminationofthepatient)andsymptoms(whatthepatientcomplainsof)areseenfollowingstroke,weneedfirsttobrieflydiscussthebloodsupplytothebrain.
1.Whilestrokecanoccurinthespinalcord,itisrare;moststrokesinvolvethebrain.
2.Theentirebloodsupplytothebrainisfromtwomajorarterial(internalcarotidandvertebral)systems.
3.Thetwointernalcarotidsgiverisetotheanteriorandmiddlecerebralarteriesthatsupplymuchofthecerebralcortex(Figure11.1)anddeepstructuresofthehemisphereswithblood.
4.Thetwovertebralarterieshavebranchessupplyingpartofthebrainstemandcerebellumwithblood.Thevertebralarteriesjointoasingleartery(thebasilar)thatsuppliestheponswithblood;thebasilardividesinitsrostralportiontoformthetwoposteriorcerebralarteriesthatsupplypartsofthecerebralcortex(Figure11.1),somedeepstructuresofthehemispheres,andsomebrainstemareaswithblood.
C.Atthebaseofthebrain,theanterior,middle,andposteriorcerebralarteriesanastomose,orjoin,toforma“circle,”knownasthecircleofWillis(namedafterthefatherofneurology,ThomasWillis).
III.Strokesoccurwhenanyofthevesselssupplyinganypartofthebrainarecompromised.Therearetwomajorkindsofstrikes.
A.Hemorrhagicstrokes(15%ofstrokes)occurwhenavesselrupturesandbleedsintothebrain.
B.Ischemicstrokes(85%ofstrokes)occurwhenthebloodsupplytosomeareaofthebrainiscompromisedbecausethevesselisoccluded(blocked),eitherfromlocalprocessedsuchasthebuildupofplaquewithinthevesselorfromatransportedclotfromsomewhereelseinthebody(forexample,aclotofbacteriafromtheheart).
IV.Ingeneral,whenthebloodsupplytoanareaofthebrainiscutoff—forwhateverreason—thefunctionofthatareaiscompromisedorlost.Forthefollowingdiscussion,welimitourselvestocorticalbranchesofvessels(Figure11.1).forareviewofBrodmann’sareas,seeFigure5.1.
A.Forexample,theprimarymotorcortex(Area4)issuppliedbybranchesofboththeanteriorandmiddlecerebralarterieswhicharethemselvesbranchesoftheinternalcarotidartery.
1.Thelateralsurfaceofthehemisphereissuppliedbythemiddlecerebralartery.Thelateralareaofmotorcortexononesidecontrolsthemovementoftheupperpartofthebodyontheother(orcontralateral)side.
2.ThemedialaspectofArea4,whichisinvolvedwithmovementofthecontralaterallowerbody,issuppliedbybranchesoftheanteriorcerebralartery;ifthesespecificbranchestothisareaarecompromised,thentheabilitytoinitiatemovementofthecontralaterallegwillbecompromised.
B.Strokescaninvolvesmallerbranches(suchastheexamplejustgiven)orcaninvolveamajorbranchorartery;forexample,theinternalcarotidgivesrisetoboththeanteriorandmiddlecerebralarteries;thusastrokeoftheinternalcarotidononesidecompromisesalloftheareassuppliedonthemedialandlateralhemispheresbythesetwocerebralarteries,andalsootherareassuppliedbytheinternalcarotid.
C.Astrokeinvolvingtheposteriorcerebralartery,ontheotherhand,wouldproduceacompletelydifferentsetofsignsandsymptoms.Astrokeinvolvingcorticalbranchesoftheposteriorcerebralartery,forexample,wouldproducealossofvisioninthecontralateralhemi-field(half)ofvisionbecausecorticalbranchesofthisarterysupplyArea17.
V.Whileanytypeofstrokeispotentiallyserious,theycanhavequitedifferentoutcomesdependingonthetypeofstrokeaswellastheareasofthebrainthatarecompromised.
A.Forexample,hemorrhagicstrokesaregenerallymoreseriousthanischemicstrokes.
1.Inhemorrhagicstroke,thebleeditselfortheformationofabloodclotcantakeupspace;becausethebrainisinaclosedcompartment,space-occupyinglesions(forexample,bloodclots)cancausethebraintoherniatedormove.
2.Downwardmovementofthebrainthroughtheforamenmagnum(wherethebrainiscontinuouswiththespinalcord)cancausedeathbecauseofcompromiseofthereticularformationnucleilocatedinthemedullawhichcontrolvitalfunctionslikebreathing.
B.Ischemicstrokescanalsopotentiallytakeupspacebyproducingbrainswelling(edema);drugsaregenerallyusedtohelpdecreasebrainedema.
1.Greatstrideshavebeenmadeinhelpingindividualssurviveischemicstrokesiftreatedearly;lossoffunctionanddisabilityfromischemicstrokecanoccurifbloodflowtotheareaisnotrestored.
2.Glutamateisimplicatedinpostischemicstrokeeventsthatcanleadtoincreaseddisability.Ischemiacausesneuronstoreleaseglutamateintotheareasurroundingtheactualstroke(calledtheischemicpenumbraorumbrellaarea).Thisplacesthesurroundingneuronsatriskiftheastrocytesintheareacannotremovethisglutamate;ifexcessive,extracellularglutamatecansetoffacascadeofeventsleadingtoadditionalneurondeath.
3.Sometimesavesselbecomesoccludedforashorttimeandthenclears,whichisreferredtoasatransientischemicattackorTIA;suchtransientevents,however,oftensignalanimpendingmajorstroke.
4.Intheeventofanysuddenonsetofneurologicalsignsorsymptoms,seekhelpimmediately.
FurtherReading:
Anyrecentneurosciencetextwillcovermostofthebasicinformationcoveredinthislecture,althoughinmuchgreaterdetail.TheauthoritativebookinneuroscienceisPrinciplesofNeuralscience,editedbyE.R.Kandel,J.H.Schwartz,andT.M.Jessell.
QuestionstoConsider:
1.Didyourealizethatthereweredifferentkindsofstrokes?
Givenwhatyouhavelearnedaboutthetwotypesofstroke,forwhattypewouldababyaspirinadaybeapreventivemeasure?
Why?
2.Whataretheriskfactorsforheartattackandstroke?
Whywouldtheybethesameforbothtypesofattack?
LectureEleven—Transcript
Stroke
Welcomebacktoourlastlectureinthisfirstsegmentofourcourse.Uptothispointwehavebeenlearningabouthowthebrainisorganized.Sowelookedatgrowth,cellularandmolecularlevels.Wealsolookedathowneuronscommunicatewitheachother.
Inthislastandfinallectureinthissegment,Iwanttousestrokeasaclinicalexampletoreinforcewhatwehavecovereduptothispointandalsotellyousomeveryimportantthingsaboutthiscriticalclinicaldisorder.
Tounderstandstrokeweneedtorealizethatthebrainisveryactivemetabolically.It’sestimatedthatalthoughthebrainaccountsforonlyaverysmallportionofthetotalbodymass,aboutoneortwopercent,itreceives20percentoftherestingcardiacoutput.Theotherthingthat’simportanttounderstandisthatthebrainhasnoability,oratleastvery,verylimitedability,tostoreeitheroxygenorglucose.And,lastly,neuronsdiewithinminutesiftheyarecutoffordeprivedofoxygen.Thus,anythingthat’sgoingtointerferewithbloodflowisvery,veryimportant,becauseitcompromisesbrainfunction.Neuronsdieandtheyaren’treplaced.Andsoitbehoovesustotakegoodcareofourneurons,andthatmeanstakingverygoodcareofthevesselsthatsupplytheoxygenandglucosetoourbrains.
Sowhatisastroke?
Well,astrokeisessentiallya“brainattack”inthesamesensethatwespeakofcompromiseofcoronaryvesselsasbeinga“heartattack.”StrokeisthethirdleadingcauseofdeathintheUnitedStatesandisthenumberonecauseofdisability.Whatwewanttocoverhereinthislectureandunderstandiswhy,whenyouhaveastroke,youhaveparticularsignsorsymptoms.Sothefirstthingwewanttodoisdefinewhatwemeanbysignsandsymptoms.Inneurology,signsarewhatarefoundonexaminationofthepatient.So,forexample,ifyourdoctorshinesalightinyoureye,theymaybelookingtoseeifyourpupilwillclosedownbecauseofthelight.Ifitfailstoclosedown,that’sasign.Ifyougotothedoctorcomplainingofaheadacheorsayingthatyouhavedevelopedheadaches,thosearesymptoms.SowehavesignsandsymptomsandI’mjustgoingtousethemtogetheraswhateverthepatientcomesinwithorwhatthedoctorfindsinexamination.
Whatwewanttolearninthislectureiswhyisitthatonepersonwhohasastrokehasdifficultytalking,whereasanotherpersonwhohasastrokehasdifficulty,say,movingtheirarm?
Andgivenwhatyouhavelearnedinthecourse,youcanprobablyanticipatewhatwearegoingtotalkabout,butit’sveryi
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