brachial plexus

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  • (https://s100.copyright.com/AppDispatchServlet?publisherName=ELS&orderBeanReset=true&orderSource=ClinicalKey&contentID=B9781416047056000181)

    BOOKCHAPTER

    BrachialPlexusElliottL.MancallMDGray'sClinicalNeuroanatomy:TheAnatomicBasisforClinicalNeuroscience,Chapter18,319345

    OverviewoftheBrachialPlexusThebrachialplexusisaunionoftheventralramiofthelowerfourcervicalnervesandthegreaterpartofthefirstthoracicventralramus(Figs18.1,18.2(f0010)).Thefourthramususuallygivesabranchtothefifth,andthefirstthoracicfrequentlyreceivesonefromthesecond.Theseventralramiaretherootsoftheplexustheyarealmostequalinsizebutvariableintheirmodeofjunction.ContributionstotheplexusbyC4andT2vary.WhenthebranchfromC4islarge,thatfromT2isfrequentlyabsentandthebranchfromT1isreduced,formingaprefixedtypeofplexus.IfthebranchfromC4issmallorabsent,thecontributionfromC5isreduced,thatfromT1islargerandthereisalwaysacontributionfromT2thisarrangementconstitutesapostfixedtypeofplexus.

  • Fig.18.1Planofthebrachialplexus.TheposteriordivisionofthetrunksandtheirderivativesareshadedthefibresfromC7thatentertheulnarnerveareshownasaheavyblackline.C4toC8andT1andT2indicatetheventralramiofthesecervicalandthoracicspinalnerves.

    Fig.18.2Diagramofthebrachialplexus,itsbranchesandthemusclestheysupply.(FromAidstotheExaminationofthePeripheralNervousSystem,4thed.2000.Saunders,London.)

    Closetotheirexitfromtheintervertebralforamina,thefifthandsixthcervicalventralramireceivegreyramicommunicantesfromthemiddlecervicalsympatheticganglion,andtheseventhandeighthramireceivegreyramifromthecervicothoracicganglion.Thefirstthoracicventralramusreceivesagreyramusfrom,andcontributesawhiteramusto,thecervicothoracicganglion.

    Themostcommonarrangementofthebrachialplexusisasfollows:thefifthandsixthramiuniteatthelateralborderofscalenusmediusastheuppertrunktheeighthcervicalandfirstthoracicramijoinbehindscalenusanteriorasthelowertrunktheseventhcervicalramusbecomesthemiddletrunk.Thethreetrunksinclinelaterally,andeitherjustaboveorbehindtheclavicle,eachbifurcatesintoanteriorandposteriordivisions.Theanteriordivisionsoftheupperandmiddletrunksformalateralcordthatlieslateraltotheaxillaryartery.Theanteriordivisionofthelowertrunkdescendsatfirstbehindandthenmedialtotheaxillaryarteryandformsthemedialcord,whichoftenreceivesabranchfromtheseventhcervicalramus.Posteriordivisionsofallthreetrunksformtheposterior

  • cord,whichisatfirstaboveandthenbehindtheaxillaryartery.Theposteriordivisionofthelowertrunkismuchsmallerthantheothersandcontainsfew,ifany,fibresfromthefirstthoracicramus.Itisfrequentlyderivedfromtheeighthcervicalramusbeforethetrunkisformed.

    OverviewofthePrincipalNervesAxillaryNerve(C5,C6)Theaxillarynerveisabranchoftheposteriorcordofthebrachialplexus.Itwindsposteriorlyaroundtheneckofthehumerustogetherwiththecircumflexhumeralvesselsandsuppliesthedeltoidandteresminorandanareaofskinoverthedeltoidregion(Fig.18.3(f0020)).

    Fig.18.3Motorandsensorybranchesoftheaxillarynerve.(FromAidstotheExaminationofthePeripheralNervousSystem,4thed.2000.Saunders,London.WithpermissionofGuarantorsofBrain.)

    RadialNerve(C58,T1)Theradialnerveisthecontinuationoftheposteriorcordofthebrachialplexus(Fig.18.4(f0025)).Intheupperarmitliesinthespiralgrooveofthehumerus,whereitisaccompaniedbytheprofundabrachiiarteryanditsvenaecomitantes.Itenterstheposterior(extensor)compartmentandsuppliestriceps,thenreenterstheanteriorcompartmentofthearmbypiercingthelateralintermuscularseptum.Atthelevelofthelateralepicondyleitgivesofftheposteriorinterosseousnerve,whichpassesbetweenthetwoheadsofthesupinatorandenterstheextensorcompartmentoftheforearm.Theposteriorinterosseousnervesuppliesthesemuscles.Theradialnerveitselfcontinuesintotheforearmintheanteriorcompartmentdeeptothebrachioradialis.Itterminatesbysupplyingtheskinovertheposterioraspectofthethumb,index,middlefingersandradialhalfoftheringfinger.

  • Fig.18.4Motorandsensorybranchesoftheradialnerve.Variationexistsinthecutaneousinnervationofthedorsalaspectsofthedigits.Here,theradialnerveisshownsupplyingallfivedigits.Thedorsumoftheringandlittlefingersisfrequentlyinnervatedbythedorsalbranchoftheulnarnerve.(FromAidstotheExaminationofthePeripheralNervousSystem,4thed.2000.Saunders,London.WithpermissionofGuarantorsofBrain.)

  • MusculocutaneousNerve(C57)Themusculocutaneousnerveisformedfromthecontinuationofthelateralcordofthebrachialplexus.Itpiercesthecoracobrachialissuppliesit,bicepsandbrachialisthencontinuesintotheforearmasthelateralcutaneousnerveoftheforearm(Fig.18.5(f0030)).

    Fig.18.5

  • Motorandsensorybranchesofthemusculocutaneousnerve.(FromAidstotheExaminationofthePeripheralNervousSystem,4thed.2000.Saunders,London.WithpermissionofGuarantorsofBrain.)

    MedianNerve(C68,T1)Themediannerveisformedbytheunionoftheterminalbranchofthelateralandmedialcordsofthebrachialplexus(Fig.18.6(f0035)).Ithasnobranchesintheupperarm.Itenterstheforearmbetweenthetwoheadsofpronatorteresandgivesofftheanteriorinterosseousnerve,whichsuppliesalltheflexormusclesoftheforearmexceptforflexorcarpiulnarisandtheulnarhalfofflexordigitorumprofundus.Themediannerveitselfpassesdeeptotheflexorretinaculumatthewrist.Onenteringthepalm,itgivesoffmotorbranchestothethenarmusclesandtheradialtwolumbricalsandcutaneousbranchestothepalmaraspectofthethumb,indexandmiddlefingersandtheradialhalfoftheringfinger.

  • Fig.18.6Motorandsensorybranchesofthemediannerve.Flexordigitorumprofundustotheringandlittlefingersissuppliedbytheulnarnerve.Flexorpollicisbrevismaybesuppliedbyboththemediannerveandtheulnarnerve.(FromAidstotheExaminationofthePeripheralNervousSystem,4thed.2000.Saunders,London.WithpermissionofGuarantorsofBrain.)

    UlnarNerve(C7,C8,T1)Theulnarnerveisthecontinuationofthemedialcordofthebrachialplexus(Fig.18.7(f0040)).Likethemediannerve,ithasnobranchesintheupperarm.Itenterstheposteriorcompartmentoftheupperarmmidwaydownitslengthbypiercingthemedialintermuscularseptumandpassesbehindthemedialepicondyleofthehumerustoentertheforearm.Itpassestothewristdeeptoflexorcarpiulnaris,givingbranchestothismuscleandtotheulnarhalfofflexordigitorumprofundus.Justproximaltothewristitgivesoffadorsalcutaneousbranchthatsuppliestheskinoverthedorsalaspectofthelittlefingerandtheulnarhalfoftheringfinger.TheulnarnervecrossesintothepalmsuperficialtotheflexorretinaculuminGuyon'scanal.Itdividesintoamotorbranch,whichsuppliesthehypothenarmuscles,theintrinsics(apartfromtheradialtwolumbricals)andadductorpollicis,andcutaneousbranches,whichsupplytheskinofthepalmaraspectofthelittlefingerandulnarhalfoftheringfinger.

  • Fig.18.7Motorandsensorybranchesoftheulnarnervetogetherwiththemedialcutaneousnervesofthearmandforearm.Flexordigitorumprofundustoindexandmiddlefingersissuppliedbythemediannerve.Flexorpollicisbrevismaybesuppliedbyboththemediannerveandtheulnarnerve.(FromAidstotheExaminationofthePeripheralNervousSystem,4thed.2000.Saunders,London.WithpermissionofGuarantorsofBrain.)

    DermatomesOurknowledgeoftheextentofindividualdermatomes,especiallyinthelimbs,isbasedlargelyonclinicalevidence(Fig.18.8(f0045)).ThedermatomesoftheupperlimbarisefromspinalnervesC58andT1.C7suppliesthecentralpartofthehand.Considerableoverlapexistsbetweenadjacentdermatomesinnervatedbynervesderivedfromconsecutivespinalcordsegments.

  • Fig.18.8Arrangementofdermatomesandcutaneousnervesoftheleftupperlimb.A,Viewedfromtheanterioraspect.Theheavyblacklinerepresentstheventralaxiallineoverlapacrossitisminimal.Inmarkedcontrast,overlapisconsiderableacrosstheinterruptedlines.B,Viewedfromtheposterioraspect.Theheavyblacklinerepresentsthedorsalaxiallineoverlapacrossthislineisminimal.Overlapisconsiderableacrosstheinterruptedlines.

    MyotomesEachspinalnerveoriginallysuppliesthemusculaturederivedfromitsownmyotome.Wheremyotomalderivativesremainentities,theyretaintheiroriginalsegmentalsupply.Whenderivativesfromadjoiningmyotomesfuse,theresultingmusclesdonotalwaysretainanervesupplyfromeachcorrespondingspinalnerve.Becausemusclesdevelopinsitu,inthemesodermalcoresofthedevelopinglimbs,itisimpossibletoidentifytheiroriginalsegmentsbyadevelopmentalstudy.Mostlimbmusclesareinnervatedbyneuronesfrommorethanonesegmentofthespinalcord.Tables18.1to18.4(t0010)summarizethepredominantsegmentaloriginsofthenervesupplyforeachoftheupperlimbmusclesandformovementstakingplaceatthejointsoftheupperlimbdamagetothesesegmentsortotheirmotorrootsresultsinmaximalparalysis.

    Table18.1Movements,musclesandsegmentalinnervationintheupperlimb

  • Table18.2Segmentalinnervationofmusclesoftheupperlimb

    C3,C4

    Trapezius,levatorscapulae

    C5 Rhomboids,deltoids,supraspinatus,infraspinatus,teresminor,biceps

    C6 Serratusanterior,latissimusdorsi,subscapularis,teresmajor,pectoralismajor(clavicularhead),biceps,coracobrachialis,brachialis,brachioradialis,supinator,extensorcarpiradialislongus

    C7 Serratusanterior,latissimusdorsi,pectoralismajor(sternalhead),pectoralisminor,triceps,pronatorteres,flexorcarpiradialis,flexordigitorumsuperficialis,extensorcarpiradialislongus,extensorcarpiradialisbrevis,extensordigitorum,extensordigitiminimi

    C8 Pectoralismajor(sternalhead),pectoralisminor,triceps,flexordigitorumsuperficialis,flexordigitorumprofundus,flexorpollicislongus,pronatorquadratus,flexorcarpiulnaris,extensorcarpiulnaris,abductorpollicislongus,extensorpollicislongus,extensorpollicisbrevis,extensorindicis,abductorpollicisbrevis,flexorpollicisbrevis,opponenspollicis

    T1 Flexordigitorumprofundus,intrinsicmusclesofthehand(exceptabductorpollicisbrevis,flexorpollicisbrevis,opponenspollicis)

    Table18.3Segmentalinnervationofjointmovementsoftheupperlimb

    Shoulder Abductorsandlateralrotators C5

    Abductorsandmedialrotators C68

    Elbow Flexors C5,C6

    Extensors C7,C8

    Forearm Supinators C6

    Pronators C7,C8

    Wrist Flexorsandextensors C6,C7

    Digits Longflexorsandextensors C7,C8

    Hand Intrinsicmuscles C8,T1

    Table18.4

  • Movementsandmu