IntroductiontotheNervousSystem.Code:HMP100/UPC103/VNP100.Course:MedicalPhysiologyLevel1MBChB/BDS/BPharmLecture1.TheOrganisationoftheNervousSystemLectureOutline1.1Introduction1.2Learningoutcomes1.3FunctionoftheNervousSystem1.4DivisionsoftheNervousSystem1.5The7divisionsoftheCentralNervousSystem1.6The5lobesoftheCerebralHemisphere1.7Summary1.8Activity1.9FurtherReading1.1IntroductionInthislecture,wewillgooverbasicaspectsoftheanatomyofthenervoussystemthatisnecessarytounderstandhowthenervoussystemfunctions,i.e.,itsneurophysiology.Inthelecture2,wewilldiscussthepartsofthenervoussysteminvolvedinsomeofthefunctionsofthenervoussystem.Andinlecture3,wewilldiscussthecellsofthenervoussystem-neuronsandglia-andlookatasimpleneuralcircuit.Oncewehavecompletedthese3lectures,wewillhavethebackgroundtostudyinmoredetailhowthenervoussystemcarriesoutitsmanydiversefunctions.1.3FunctionsoftheNervousSystem

Thenervoussystemisacomplexorganwithextraordinaryfunctions,suchasmemory,learning,language,andmovement.Italsotheorganofourbodythatsees,hears,tastes,createsemotions,controlsoursleep/wakecycleaswellasbeingcreativeandsolvingproblem.Itistheorganthatmakesuswhoweare.Andwecanimaginethatanorganthatcarriesoutsomanyextraordinary

1.2LearningOutcomesAttheendofthislecture,youshouldbeableto:1. StatethefunctionoftheNervousSystem2. NamethedivisionsoftheNervousSystem3. Drawandlabelthe7divisionsoftheCentralNervousSystem4. Drawandlabelthe5lobesofthecerebralhemispheres5. Drawtheorganisationofthespinalcord6. Describetheorganisationofthespinalcord

functionswillbequitecomplexinitsorganisation.Butletusdonotpanic,wedonotneedtoknoweverysinglethingaboutthenervoussystemforthiscourse.However,wedoneedtoknowthebasicthingsaboutthenervoussystemandhowingeneralhowthenervoussystemfunctions.Whatwewilllearnfromtheselecturesonthenervoussystemwillbeusefulinmanydifferenteducationalandprofessionalareas.Someexamplesoftheareaswhereunderstandingofthenervoussystemisusefulareneurology,psychiatry,behaviouralscience,neuropharmacology,psychology,physiotherapy,nursingscience,dentistry,educationandeveneconomics.Ourbodiescontain10physiologicalsystems:cardiovascular,respiratory,renal,gastrointestinal,endocrine,neuronal,integumentary,reproductive,musculoskeletal,andimmune.Ofthese10physiologicalsystems,9arenecessaryforsurvivaland1,thereproductivesystem,forthepropagationofthespecies.Fromotherlecturesinphysiology,welearntthattheoverallfunctionofourphysiologicalsystemsistomaintainhomeostasis,whichthemaintenanceoftheconstancyofthechemicalandphysicalcompositionofourinternalenvironment.Theinternalenvironmentisthefluidthatsurroundsallourcellsanditschemicalandphysicalpropertiesneedtobemaintainedwithinarangeofvaluessoourcellscanfunctionnormally.Forexample,ifthereischangeintheelectrolytes(Na+,K+,Ca2+,Cl-)concentrations,notonlywillsignalinginthenervoussystembeaffectedbutalsoourheartrhythm.Becausetherearemanyvariablesthathavetocontrolledforhomeostasis,differentphysiologicalsystemsarenecessary.But,howistheactivityofthesephysiologicalsystemscontrolledandhowistheiractivitycoordinated?Wehave2physiologicalcontrolsystems:theendocrinalandtheneuronal,thatcontrolandcoordinatetheactivityoftheotherphysiologicalsystems.Theendocrinesystem,whichwewilllearnaboutinlaterlectures,operatesslowlyanditseffectscanlastfromminstodaystoyears.Forexample,atpubertyhormonesarereleasedthatcausechangeinourphysicalstructureandthesechangesarenotreversibleandwillremainwithusfortherestofourlives.Theneuronalsystemisfasterthantheendocrinesystemanditsactivityisturnedonandoffrapidly.(Itworksonamillisecondtimescale).Itisalsothesystemthroughwhichinformationabouttheexternalandinternalenvironmentisreceivedandprocessed.Ithasreceptorsandsensoryorgans(detectors)thatrespondtophysicalforces,energies,andchemicalsthatarepresentinourinternalandexternalenvironment.Forexample,theretina,whichislocatedatthebackoftheeye,containsspecialreceptorsthatrespondtoelectromagneticradiation,whichwecallvisiblelight,andthesignalsproducedfromthesereceptorsareusedtoproduceimagesoftheexternalenvironment.Insideourbody,therearealsoreceptorsthatrespondtochangesinbloodpressure,pH,temperatureandothervariables.So,forexample,ifourbodypHgoesdown,i.e.,becomesmoreacidic,thenervoussystemstartsacompensationprocesswhichincludesincreasetherateanddepthofourbreathingsotoincreasethepHandbringbackitsvaluewithinthenormalrange,andhormonalchangestoincreasetheexcretionofhydrogenionsintheurine.

Wewilllearnaboutthenervoussysteminatleast4coursesthatyouwilltakeinlevel1and2courseofstudiesforthedegreeMBChB/BPharm/BDS.Wewilllearnneuroanatomyin1styearhumananatomy,wewilllearnneurochemistryinour1stand2ndyearofBiochemistrycourses,and,ofcourse,wewilllearnhowthenervoussystemfunctions(neurophysiology)inour1stand2ndyearmedicalphysiologycourses.Sowewillhaveseveralopportunitiestolearnaboutthemanydifferentaspectsnervoussystemfromitsanatomicalorganization,toitschemistryandfinallythemechanismofitsfunction.

Before,wediscusshowthenervoussystemfunctions,wewillneedtoknowsomeanatomyofthenervoussystem.Asalreadymentioned,wewilllearnneuroanatomyinmoredetailinyourhumananatomycourse.Here,ourpurposeistoknowenoughanatomicaldetailsofthenervoussystemtounderstandhowthenervoussystemworks.

1.4DivisionsoftheNervousSystemTostudyandlearnaboutthenervoussystem,wefirstdividethenervoussysteminto2majordivisions:(1)thecentralnervoussystem(CNS)and(2)theperipheralnervoussystem(PNS).Now,thoughthesetwodivisionsarepartofthenervoussystem,theyexistindifferentenvironment.TheCNSisenclosedbybonesofthevertebralcolumn,skull,andmembranes.ThiscreatesaseparateenvironmentfortheCNSfromthePNS.Thereisablood-brainbarrier,whichwewilllearnaboutinlaterlectures.ItisaphysiologicalbarrierthatcontrolswhatsubstancescanenterandleaveourCNS.TheboundarybetweenourCNSandPNSisthetoughleatheryoutercoveringoftheCNScalledtheduramater.WecanfurtherdividetheCNSintotwoparts:thespinalcordwhichislocatedinthevertebralcolumn,andthebrain,whichislocatedinsidetheskull.SothewholeoftheCNSisverywellprotectedbybeingsurroundedbythickbones.

Inwhichcourseswillwehaveopportunitytolearnaboutthenervoussystem?

Namethe10physiologicalsystemsthatarepresentinyourbody.

Thiswecanbeseeinfigure1,whichshowsthesaggitalsectionofperson’sheadandneck.Wecanseehowthickaretheskullandvertebralbones

Figure1.1AMagneticResonanceImage(MRI)ofthesagittalsectionofhumanheadandneck.(Neuroanatomy,JackMartin)Figure1.2isadiagramofthePNS.Itismadeupof31pairsofspinalnervesandcranialnerves,andthenervefibersthatgotoallpartsofthebody.

Figure1.2Diagramoftheperipheralnervoussystem.(source:medcalterms.info)Figure1.3showsthespinalcord.Wecanseethatthereisadarkerregioninsidethespinalcord.Thisiscalledthegraymatterandthespinalcordnervecellsarelocatedhere.Surroundingthisgraymatterisalighterregioncalledthewhite

matter,whichconsistsofnervefibresgoinguptoandcomingdownfromthebrain.

Figure1.3Spinalcordandthespinalnerves.(Source:facutly.ucc.edu)Thespinalnervehastworoots:(1)Theventralroot,labelledA,throughwhichnervefibresofthenervecellsinthegraymatterleavethespinalcord,and(2)thedorsalroot,labelledD,throughwhichnervefibresenterthespinalcord.Thenervecellsofthenervefibresofthedorsalrootareoutsidethespinalcordinswellingswecanseeinthedorsalroot(WherethearrowheadofDistouchingthedorsalspinalcord).Thesearecalledthedorsalrootgangliaandrunaschainalongthelengthofthevertebralcolumn-thedorsalrootgangliachain.

Figure1.4OrganisationoftheNervousSystem.Source:Purvesetal.Fig10.1Figure1.4,showsthedivisionofthenervoussystemintoCNS(colouredyellow-brown)andPNS(purplecoloured).Studyingfigure1.4,wecanseethattheCNScommunicateswiththePNSandthePNScommunicateswithdifferenttissuesofourbody.SotheCNScontrolstheactivitiesofthesetissuesthroughthePNS.Thereisthemotorpartofnervoussystem(thelightpurplecolor)andasensorysystem(darkerpurplecolour).ThesignalsfromthereceptorsonourskinandinsideourbodiesaresendthroughthePNStotheCNS.w

SoourPNSissub-dividedinto2parts:amotorpartandasensorypartandthemotorpartisfurtherdividedinto(1)somaticmotorsystem,whichcontrolsallourskeletalmuscles,and(2)visceralmotorsystemwhichcontrolsthesmoothmusclesofinternalorgans,thecardiacmuscle,andglandularactivityinsideourbody.Thevisceralmotorsystemitselfisfurtherdividedintothesympathetic,parasympathetic,andentericdivisions.Thesympatheticandparasympathetic

1. Whatarethe2divisionsofthemotorcomponentofperipheralnervoussystem?

2. Whattissuesarecontrolledbythese2divisions?3. Whatarethe3divisionsofthevisceralmotorsystem?

togethermakeuptheautonomicnervoussystem(ANS).Theentericnervoussystemisfoundwithinthewallsofourgastrointestinaltract.Inthelecturesongastrointestinalphysiology,wewilllearnmoreabouttheentericnervoussystem.Sointhissection,wehavelearntthatthenervoussystemisdividedinto2majordivisions:CNSandPNS,andthePNSisfurthersub-dividedintotwomajordivisions:somaticandvisceralmotorsystem,andthevisceralmotorsystemisfurtherdividedinto3sub-divions.Inthenextsection,wewilllookatsub-divisionsoftheCNS.StudyAide:Agoodstudyaideistodrawthediagramsandlabelthem.Wewillfindthisreinforcesourmemoryandhavingaclearmentalpictureofthenervoussystemwillhelpusinlearningaboutthenervoussystemeasier.1.5TheSevenDivisionsoftheCentralNervousSystemInsection,wewillidentifyandlocatethe7sub-divisionsoftheCNS.Figure1.5showsasaggitalviewofaperson’sheadtakenwiththetechniqueofmagneticresonanceimaging(MRI).TheMRIproducesdetailedimagesoflivingtissuethatareusedusedalotinthehealthcareprofessionfordiagnosispurposes.Now,startingfrombottomofthepicture,weseethepartoftheCNScalledthespinalcordlocatedwithinthevertebralcolumn(colouredinpurple).Theupperboundaryofthespinalcordisatthebaseoftheskull,andlowerendinanadultisaboutthe2ndlumbarvertebra.Thenaswemoveupthroughtheholeinthebaseoftheskull(foramenMagnum),wecometothemedullaoblongata(colouredinyellow).ThisisaveryimportantpartoftheCNS.Itcontrolsourbreathingandheartrate.DamagetothisareaofourCNSwillresultindeath.Infact,deathisthedyingofthenervecellsinthemedullaoblongata.Continuingtomoveup,wecometothethirdpartoftheCNS-thepons(showninorange).AndontopoftheponswecometothefourthpartoftheCNS–themidbrain(showningreencolour).Abovethemidbrain,theregioncolouredpurpleisthediencephalon.Themedulla,pons,midbrain,anddiencephalonarecollectivelycalledthebrainstem.

Figure1.5Sagittalsectionoftheupperpartofthespinalcordandthebrainshowingthe7divisionsofthenervoussystem.(Source:JackMartin,TeachingToolsinNeuroscience,Ethiopia,2015)Sowehavenowcovered5divisionsoftheCNS.Thefinal2arethecerebellumandthecerebralhemispheres.Thecerebellumisshowninapurplecolourjuttingoutfromthebrainstem.Thispartofthebrainisveryimportantinthecontrolofmovement.Sittingontopofthebrainstem,showninpink,arethehugecerebralhemispheres.Theyarecalledthehemispheres(halfspheres)becausewehavetwoofthem,oneintherightsideofourskullandtheotherintheleftpartofourskull.Inthissection,wehavelearntaboutthe7sub-divisionsoftheCNS.

1.6The5LobesoftheCerebralHemispheresNowwecontinuetosub-dividetheCNS.Herewewilllookathowthesurfaceofthecerebralhemispheresisdividedinto4lobes:frontal,parietal,temporal,andoccipital.

1. Drawadiagramofthebraininthesaggitalplaneandlabelthe6divisionsoftheCNSfoundinsidetheskull.

2. Whatdoestheword‘diencephalon’meaninplainEnglish?

Howwerethesedivisionsdone?Howonthesurfaceofthecerebralhemispherescantheselobesbeidentified?Thesearequestionsthatwewillbelookingatinthefollowingpartofthelecture.Figure1.6,showsaphotographofahumanbrain,inparticular,thelateralviewofthecerebralhemispheres.Youcanseethatthesurfaceofthecerebralhemispherehasfoldsorwrinkles.Thesefoldsorwrinklesarecalledthesulci(singular:sulcus)andtheareasbetweenthesulciarecalledthegyri(singular:gyrus).Sothesurfaceofthebrainlookslikealargepieceofpaperthathasbeencrumpledtofitintoasmallspace.

Figure1.6.Lateralviewoftheleftcerebralhemisphere.Thefrontistowardstheright.Ifwetakeadozenorsohumanbrainsandcomparethem,westarttonoticethatthereissimilarityofpatterninthesulciandgyribetweentheindividualhumanbrains.Eachhumanbrainhasroughlysimilarpatternofsulciandgyri.Wecanusetheregularityofthepatternofsulciandgyriasgeographicalmarkersonthesurfaceofthecerebralhemispheres.Whilethesurfaceofthebrainlooksverycomplicated,showingquiteanumberofsulciandgyri,therearenotmanysulciandgyrithatwehavetolearnthenamesandlocationof.StudyAide:Averygoodexerciseistodrawoutthelateral(side)andsagittal(middle)viewofthebrainwithallthesulcidrawn.Thiswayyouwillquicklylearnthefeaturesofthesurfaceofthecerebralhemispheresandthenamesofthemajorgyrithatformtheboundariesofthedifferentlobes.OnYouTubeyoucanwillfindvideosshowinghowtodrawtheseviews.Letusfindtheboundariesofthe4lobesofthecerebralhemispheres.Ifwelookdownatthebrainfromthetop,youseeadeepdivisionbetweenthetwocerebralhemispheres.Thiscalledthemediallongitudinalfissure.Lookingatthebrainfromthelateralside,wecanseeanotherdeepspace,runningatanangle,fromthefronttowardsthebackofthebrain.ThisisthelateralfissureortheSylvanfissure.(Thedifferencebetweenasulcusandfissureisthatafissureisdeeper

thanasulcus.)Animportantsulcusisthecentralsulcus.Thisrunsallthewayfromthetopofeachcerebralhemispheretothelateralfissure.Thisisnicelyshowninfigure1.7withthelateralfissureandthecentralsulcusmarkedinred.

Figure1.7Thelateralviewofthebrainsurface.(Thefrontofthebrainistowardstheright.)(Source:en.wikipedia.org)Sousingthefissuresandsulciaslandmarks,thesurfaceofthecerebralhemispherescanbedividedinto4majorlobes.Theareainfrontofthecentralsulcusgoingdowntothelateralfissureisthefrontallobe.Theareabehindthecentralsulcusdowntothelateralfissureandgoingbacktotheparito-occipitalsulcusonthetopofthecerebralhemisphereistheparietallobe.Theareagoingtothebackofthecerebralhemispherefromtheparito-occipitalsulcusistheoccipitallobe.Theareaofcortexbelowthelateralfissureisthetemporallobe.Atthepointwheretheparietal,temporalandoccipitallobesmeet,thereisnophysicalboundary.Itisanimaginedboundary.Ifwelookatthemedialsurfaceofthecerebralhemisphereinfigure1.8wecanseethatlobesalsoextendontothemedialsurface.Also,hereinthemedialsurface,wecanseethe5thlobe,whichiscalledthelimbiclobe.Wewilllearnmoreaboutthislobewhenwestudythenervoussystempartsthatareinvolvedinproducingemotionandmotivation

Figure1.8.Themedialsurfaceofthecerebralhemispheresshowinghowfaronthemedialsurfacethefrontal,parietal,occipitalandtemporallobesextend.Thethelimbiclobeisalsoshown.(Source:en.wikipedia.org)Thelobesalsoextendroundthebaseofthecerebralhemispheres.Thisisshowninfigure1.9.Inthesamefigureoffixedhumanbrain,wecanseewhatthemedullaoblongataandtheponslooklike.Wecanseea“white”crossinmiddlejustinfrontoftwoovalishswelling.Thisistheopticnervecarryingelectricalsignalsfromtheretinainoureyestothebrain.Wewillmoreabouttheseinthelecturesonvisualfunction.

Figure1.9.Thelobesofthebrainextendroundthebaseofthecerebralhemisphereseyearesendtotheoccipitallobe.Inalivingbrainthecutendswouldextendtoyoureyes.(Source:en.wikipedia.org)Thebonesoftheskulloverlyingthe4lobesonthelateralsurfaceofthecerebralhemispheresarealsonamedbythelobestheboneslieover.Soknowingthenamesofthebonesoftheskull,wealsoknowthenamesofthelobes.

Ifwegobacktothefigure1.8,showingthemedialviewofcerebralhemisphere,youcanseeaC-shapedstructure,coloredinwhite,inthemiddle.Thisisthecorpuscallosumbecauseitisalarge,hencecallosum,nervefibertractthroughwhichthetwocerebralhemispherescommunicatewitheachother.

Inthepictureofthelateralsurfaceofthecerebralhemispheresmarkoutandlabelthe4lobesseenonthelateralsurfaceofthecerebralhemisphere.

Brodmann’sClassificationBeforeweleavethediscussiononthemethodofdecidingonsub-divisionsofthecerebralhemispheres,weneedtodiscussanothermethodthatisusedtomarkoutdifferentareasofthesurfaceofthecerebralhemisphere.Itisimportantforyoutoknowthisclassificationmethodbecauseitisalsousedinclinicalstudestotalkaboutspecificareasofthecerebralhemispheres.Thismethod,calledBrodmann’sclassification,dividesupthebraininto50parts,andsoitcreatesamorefinerdivisionthanthemethodusedforthelobedivisions.Themethodisbasedontheorganisationofthenervecells(cytoarchitecture)inthedifferentareasofthecortexofthecerebralhemispheres.Inthisclassification,thedifferentregionsarelabelledbynumbersratherthanlettersor

words.

Anumberofstudentswhenaskedtodrawadiagramoftheneuronalcircuitryinvolvingthespinalcordputthenervecellbodiesinthewhitematterofthespinalcord.Thisisabsolutelywrongandyouwillgetazeromarkformakingsuchatrivialmistake.

Figure1.10.ThesurfaceofthecerebralhemispheredividedintodifferentareasusingtheBrodmann’sclassificationwhichisbasedonthecytoarchitectureinthedifferentpartsofthecerebralhemispheresurface.

AwaytorememberthedifferencebetweenAfferentandEfferentisAisforarrivalofneuronalsignalstothespinalcordandEisforneuronalsignalsthatexitthespinalcord.

Usefulmethodtolearnistodrawtreediagrams.Sodrawanupsidedowntreediagramstartingwiththenervoussystematthetopandallthedivisionsandsubdivisionsasyougodown.

Sointhissection,wehavediscussedhowthefoldsandwrinklesonthesurfaceofthecerebralhemisphereareusedtomarkthe4majorlobesofthecerebralhemispheresandtheiranatomicallocation.Sonowwehavecoveredthebasicorganisationofthenervoussystem.Inthenextlecturewewilllookatthebrainfromthepointofviewoffunction.Wewillbeaskingthequestion:Whatpartsofnervoussystemareinvolvedinthedifferentfunctionsthenervoussystem,howtheyareorganized,andhowthefunctioniscarriedout?1.7SummaryInthisfirstlectureontheintroductiontotheNervousSystem,wehavelearntthatthenervoussystemisdividedintodifferentdivisionsandthanthesedivisionhavesub-divisions.Wehavelearntofthe7divisionsoftheCNS,the3divisionsofthePNSandtheorganisationofthespinalcord.

Confusingonwhichsideofthespinalcordthesensoryinputcomesinfromwhichsidethemotoroutputleavesthespinalcordisanotherelementarymistakestudentmake.Inputisdorsal;outputisventral.

1.8Activity1.9ReadingmaterialSampleExamQuestionsMultipleChoiceQuestions(MCQs)Selectforeachquestion,thebestcorrectanswer.1) Thesulciorfissuredividingthefrontallobefromtheparietallobe.

a) Mediallongitudinalfissureb) Centralsulcusc) Lateralfissured) Parieto-occipitalfissuree) Slyvianfissure

2) Theauditorycortexislocatedonthea) Superiortemporalgyrusb) Superiorfrontalgyrusc) Middletemporalgyrusd) Middlefrontalgyruse) Inferiortemporalgyrus

3) Thenervefibertractwhichtheleftandrightcerebralhemispheresusetocommunicatewitheachotherisa) Corticospinaltractb) Corpuscallosumc) Spinothalamictractd) Sensorytracte) Cerebralpenduncles

4) Themotorpathwaycrossthenervoussystemmidlineata) Diencephalonb) Midbrainc) Ponsd) Medullae) Spinalcord

5) Insensorysystemthecrossoverofthenervefiberstotheothersidetakesplaceinthea) Diencephalonb) Midbrainc) Ponsd) Medullae) Spinalcord

ShortAnswerQuestions(SAQs)Note:SAQshavemaximumof5marks.Theanswertothequestionhastobeprecisegivingallthekeypointsrequired.IftheSAQrequiresadiagramor

illustration,wemustprovidethedrawingotherwisewewillimmediatelylosehalfthemarks.Weshouldpracticedrawingoutkeyillustrationordiagramsgiveninthelectureandinthetextbooks.

1. Describethedivisionsofthenervoussystem.

2. Drawadiagramofthelateralsurfaceofthecerebralhemisphereshowingthe4lobesandthenamingthemainsulciandgyrithatmakeuptheboundaries.

3. Withanillustrationofthesagittalareaofthecentralnervoussystem

(CNS)labelthe7divisionsoftheCNS.

4. Drawthelateralsurfaceofthelefthemisphereandshowthelocationoftheprimarymotorcortex,theprimarysensorycortex,theprimaryvisualcortex,andtheprimaryauditorycortex.