Nervous System for B sc Nursing students

for B sc Nursing students

1. NERVOUSSYSTEM
Nervoussystemcontrolsalltheactivitiesofthebody.Itisquickerthantheothercontrol
systeminthebodynamely,theendocrinesystem.Primarilythenervoussystemis
dividedintotwoparts.
1.CentralNervousSystem(CNS)
2.PeripheralNervousSystem(PNS).
CENTRALNERVOUSSYSTEM
TheCentralnervoussystemincludesbrainandspinalcord.Itisformedby
neuronsandthesupportingcellscalledneuroglia.Thestructuresofbrainand
spinalcordarearrangedintwolayersnamely,thegraymatterandwhitematter.
Thegraymatterisformedbynervecellbodiesandtheproximalpartsnerve
fibersarisingfromthenervecellbody.Thewhitematterisformedbynerve
fibers.Inbrainthewhitematteriscentrallyplacedandthegraymatterisin
theouterpart.Inspinalcordwhitematterisintheouterpartandgraymatter
isintheinnerpart.
Brainissituatedintheskull.Brainandspinalcordaresurroundedbythree
layersofmeningescalledtheouterduramater,middlearachnoidmaterand
innerpiamater.Thespacebetweenthearachnoidmaterandpiamateris
knownassubarachnoidspace.Thisspaceisfilledwithafluidcalled
cerebrospinalfluid.Thebrainandspinalcordareactuallysuspendedinthe
cerebrospinalfluid.
PERIPHERALNERVOUSSYSTEM
Theperipheralnervoussystemisformedbytheneuronsandtheirprocesses
presentinallregionsofthebody.Itconsistsofcranialnervesarisingfrom
brainandspinalnervesarisingfromspinalcord.Itisagaindividedinto2
subdivisions.
1.Somaticnervoussystem:-Itisconcernedwithsomaticfunctions.Itincludesthenerves
supplyingtheskeletalmuscles.Somaticnervoussystemcontrolsthemovementsofthe
bodybyactingontheskeletalmuscles.
2.Autonomicnervoussystem:-Itisconcernedwithregulationofvisceralorvegetative

2. functions.So,itisotherwisecalledvegetativeorinvoluntarynervoussystem.TheANS
consistsof2divisions,sympatheticdivisionsndparasympatheticdivision.
NEURON
Neuronisdefinedasthestructuralandfunctionalunitofthenervoussystem.Itis
otherwisecallednervecell.Neuronislikeanyothercellinthebodyhavingnucleusandall
theorganellesinthecytoplasm.However,itisdifferentfromothercellsbytwoways:
a.Neuronhasbranchesorprocessescalledaxonanddendrites.
b.Neurondoesnothavecentrosome;soitcannotundergodivision.
CLASSIFICATIONOFNEURON
Theneuronsareclassifiedthreedifferentmethods.
Dependinguponthenumberofpoles:-Basedonthenumberofpolesfromwhichthe
nervefibersarise,neuronsaredividedintothreetypes.
UnipolarNeurons–Unipolarneuronsaretheneuronsthathaveonlyonepole.From
thesinglepole,boththeprocesses–axonanddendritearise.Thistypeofnerve
cellsispresentonlyinembryonicstageinhumanbeings.
Bipolarneurons–Theneuronswithtwopolesareknownasbipolarneurons.Axon
arisesfromonepoleanddendritesarisefromtheotherpole.
MultipolarNeurons–Multipolarneuronsaretheneuronswhichhavemanypoles.
Oneofthepolesgivesrisetotheaxonand,alltheotherpolesgiverisetodendrites.
Dependinguponthefunction:-Onthebasisoffunction,thenervecellsareclassified
intotwotypes.
1.Motorneuron–Whichcarrythemotorimpulsesfromcentralnervoussystemto
theperipheraleffectororganslikemuscles,glands,bloodvessels,etc.Motor
neuronsarealsoknownasefferentnervecells.Generally,thoseneuronshave
longaxonsandshortdendrites.
2.Sensoryneurons–Sensorynervecellsarealsocalledafferentnervecells.These
neuronscarrythesensoryimpulsesfromperipherytothecentralnervoussystem.
Generally,thesensoryneuronshaveashortaxonandlongdendrites.
Dependinguponthelengthoftheaxon,neuronsaredividedintotwotypes:
1.GolgitypeIneurons–Ithavelongaxons.Thecellbodyoftheseneuronsis
centralnervoussystemandtheiraxonsreachtheremoteperipheralorgans.
2.GolgitypeIIneurons–Theneuronsofthistypehaveshortaxons.These

3. neuronsarepresentincerebralcortexandspinalcord.
STRUCTUREOFNEURON
Eachneuronismadeupofthreeparts:Nervecellbody,dendriteandaxon.The
dendriteandaxontogetherformtheprocessesofneuron.Ingeneral,thedendritesare
shortprocessesandtheandtheaxonsarelongprocesses.Thedendritesandaxonsare
usuallycallednervefibers.
Nervecellbody:ThenervecellbodyisalsoknownasSomaorperikaryon.Thenervecell
bodyisirregularinshapelikeanyothercellitisconstitutedbyamassofcytoplasmcalled
neuroplasmwhichiscoveredbyacellmembrane.Thecytoplasmcontainsalargenucleus,
Nisslgranules,neurofibrils,mitochondriaandGolgiapparatus.Nisslbodiesand
neurofibrilsarefoundonlyinnervecellandnotinothercells.
Dendrite:Thedendriteisthebranchedprocessoftheneuronanditisbranchedrepeatedly.
Thedendritemaybeabsentorifpresent.Itmaybeoneormanyinnumber.Thedendrite
hasNisslgranulesandneurofibrils.Ittransmitsimpulsestowardsthenervecellbody.
Usuallythedendriteisshorterthantheaxon.
Axon:Theaxonisthelongerprocessofthenervecell.Eachneuronhasonlyoneaxon.
TheaxonarisesfromaxonhillockofthenervecellbodyanditisdevoidofNisslgranules.
Theaxonextendsforalongdistanceawayfromthenervecellbody.Thelengthofthe
longestaxonisaboutonemeter.
MyelinSheath:Myelinsheathisathicklipoproteinsheaththatinsulatesthemyelinated
nervefiber.Myelinsheathisnotacontinuoussheath.Itisabsentatregularintervals.
TheareawherethemyelinsheathisabsentiscallednodeofRanvier.Thesegmentofthe
nervefiberbetweentwonodesiscalledinternode.Myelinsheathisresponsibleforthe
whitecolourofthenervefibers.Myelinsheathisformedbyconcentriclayersofproteins
alternatingwithlipids.Thelipidsarecholesterol,lecithinandcerebroside.
Myelinogenesis:Theformationofmyelinsheatharoundtheaxoniscalledthe
myelinogenesis.ItisformedbySchwanncellsinneurilemma.Beforemyelinogenesis,
Schwanncellsoftheneurilemmaareveryclosetoaxolemmaasinthecaseofunmyelinated
nervefiber.ThemembraneoftheSchwanncellisdoublelayered.TheScwanncellswrap
upandrotatearoundtheaxiscylinderinmanyconcentriclayers.Theconcentriclayers
fusetoproducethemyelinsheathbutthecytoplasmofthecellisnotdeposited.
OutermostmembraneofSchwanncellremainsasneurilemma.Nucleusofthesecells

4. remainsinbetweenmyelinsheathandneurilemma.
FunctionsofMyelinSheath:(1).Myelinsheathisresponsibleforfasterconductionof
impulsethroughthenervefibers.(2).Myelinsheathhasahighinsulatingcapacity.
Becauseofthisquality,themyelinsheathrestrictsthenerveimpulsewithinthesinglenerve
fiber.
FUNCTIONSOFNEURONS
1.Conductionofnerveimpulse-afferentneuronsconveysinformationfromtissuesand
organsintotheCNS.EfferentneuronstransmitsignalsfromtheCNStotheeffector
cells.InterneuronsconnectneuronswithinthespecificregionsoftheCNS.
NEUROGLIA
TheyarethesupportingtissueintheCNSandiscomposedof5typesofcells-
Astrocytes,Microglia,Oligodendrocytes,SchwanncellsandEpendymalcells.
1.Astrocytes-arethestar-shapedcellswithmultipleradiatingcytoplasmicprocesses.
Thesehavealltheorganellesofanormalcellandalsohavelongprocesses.
Astrocytesparticipatewiththebloodvesselendotheliumtoformapermeability
barriercalledtheBlood-BrainBarrier,betweenthebloodandnervecells.
2.OligodendrocytesandSchwanncells-arecomparativelysmallerandhaveless
processthantheastrocytes.Theyformthemyelinsheathonthenervefibersinthe
CNSbutunliketheSchwanncells,theoligodendrocytesformmyelinsheathofmany
fibersatatime.Thesearealsopresentingraymatteraroudthecellbodiesofthe
neurons.Thesearealsocalledneurilemmacells.Oligodendrocytesformmyelin
sheathfortheneuronsinthebrainandSchwanncellsformmyelinsheathforthe
neuronsoutsidethebrain.
3.Microglia-aresmallcellswithlongandthinprocesseswhichlooklikespines.These
arebelievedtobederivedfrombloodandphagocyticinactionandmotile.Ithelpsin
theremovalofbacteriaandcelldebrisfromtheCNS.
4.Ependymalcells-linethefluid-filledcavitieswithinheCNS,someependymalcells
produceCSFandothershelpmovethroughtheCNS.
STIMULUS
Astimulusisachangeintheenvironmentthatcanactivatecertainsensoryneurons.
Thestimulusmustoccurwithinthesensoryneuron’sreceptivefield,theregionthatcan

5. respondtostimulation.
Transduction-Asensoryreceptororsenseorganmustrespondtothestimulusand
transducerorconvertittogeneratepotential.Asensoryreceptororsenseorganisa
specializedcellortypeofneuronthatisselectivelysensitivetoparticularstimuli.Fore.g.
odorantmoleculesintheairstimulateolfactoryreceptorsinthenose,whichtransducerthe
molecularchemicalenergyintoelectricalenergyintheformofgeneratorpotential.
Impulsegenerationandconduction-whenageneratorpotentialreachesthreshold,itelicits
oneormorenerveimpulses.SensoryneuronsthatpropagateimpulsesintotheCNSare
calledFirstorderneurons(afferentneurons).ThepartofCNSintegratesthesensorynerve
impulseintoasensation.Mostconscioussensationsorperceptionsoccurinthecerebral
cortex.ThispartoftheCNSactsastheintegratingcenterandsendstheresponsetothe
stimulusthroughanotherneuronscalledMotorneurons(efferentneurons).
CONDUCTIONOFNERVEIMPULSE
Nerveimpulsemaybedefinedasanelectrochemicalchangeoccurringinthe
membraneofanervefiberwhenthenerveisstimulated.Thepassageofimpulsealongthe
nerveiscalledconductionofnerveimpulse.
Whenareceptorisstimulated,thestimulusistransformedintoanimpulse.Normally
theflowofimpulseisunidirectionalinthenervefibers.Iamotorneuron,impulseflowfrom
thesomaorcellbodytotheaxonandinsensoryneuron,theimpulseflowfromtheaxonto
thesoma.
Therateofnerveimpulsevariesindifferentnervefibers.Itisfasterinthicknerve
fibersandslowerinthinner.Itmovesfasterinmyelinatednervefibersandslowerin
unmyelinated.Thevelocityisgenerally1-300m/sec.Thetransmissionofnerveimpulse
isametabolicprocess.Itinvolvestheactivetransportofionsacrossthemembraneof
nervefiber.Thisprocessinvolvestheconsumptionofoxygen,releaseofcarbondioxide
andtheproductionofheat.
Thenervefiberisalongtubefilledwithaxoplasmandcoveredbyplasmamembrane.
Theaxoplasmcontainslargeamountofnegativelychargedions.Hence,outsideofthe
nervefiberispositivelychargedandinsideisnegativelycharged.Inarestingnervefiber,
theaxoplasmcontainsmoreK+andoutsidethenervefiberismoreNa+.Therestingnerve
fibermembraneismorepermeabletoK+ions.SomoreK+ionsaretransportedfrom
insidetooutside.Atthesametime,Na+aretransportedfromoutsidetoinsidebutata

6. slowerrate.Whenthenerveisstimulated,themembraneofnervefiberbecomesmore
permeabletoNa+thantoK+.HencemoreNa+moveinandlessK+moveout.Asaresult,
theinsideofnervefiberbecomespositivelychargedandoutsidebecomesnegatively
charged.
Afterthetransmissionofimpulse,themembraneofnervefiberagainbecomesmore
permeabletoK+thanNa+.HencemoreK+passesoutandlessNa+movein.Thusonce
againtheoutsidebecomespositivelychargedandinsidenegativelycharged.Theactive
transportofNa+andK+acrossthemembraneiscalledNa+/K+pump.
Thereare4typesofimpulseconduction:
1.Conductionofimpulsethroughanunmyelinatedneuron.
2.Conductionofimpulsethroughamyelinatedneuron.
3.Conductionofimpulsethroughsynapse.
4.Conductionofimpulsethroughneuromuscularjunction.
CONDUCTIONOFIMPULSETHROUGHUNMYELINATEDNEURON
TheimpulseisconductedbythemechanismofNa+/K+pump.Anervefiberisinthe
formofalongtubefilledwithaxoplasmandcoveredwithaplasmamembrane.Inresting
nervefiber,theaxoplasmisnegativelychargedandtheoutsidepositivelycharged.The
axoplasmcontainsmoreK+andoutsidecontainsmoreNa+.Inrestingstate,moreK+
moveoutandlessNa+move.Hencetheplasmamembraneofarestingnervefiberis
polarizedwiththeoutsidebeingpositiveandinsidenegative.Thisdifferenceinelectrical
potentialonthe2sidesofplasmamembraneofanervefiberistermedasResting
MembranePotential.TheRMPisabout70mV-90mV.Thenervefiberatthisstateissaid
tobepolarized.
Thepolarizedstateofthenervefiberhasthefollowingsalientfeatures:-
1.Itistherestingstateofanervefiber.
2.TheaxoplasmisnegativelychargedandECFpositivelycharged.
3.PlasmamembraneismorepermeabletoK+thanNa+.
4.MoreK+moveoutandlessNa+movein.
Whenanervefiberisstimulated,theplasmamembranebecomesmorepermeabletoNa+
thantoK+.Asaresult,moreNa+quicklymovesintotheaxoplasmandtherateofflowof
K+totheoutsideislowered.Sotheaxoplasmbecomespositivelychargedandoutside
negativelycharged.ThisreversalofelectricalchangeiscalledDepolarization.

7. CENTRALNERVOUSSYSTEM
BrainisthemostimportantpartoftheCNSthatcontrolsandco-ordinatesallthebody
functions.Itiswellprotectedfromoutsidebyahardbonyskull.Inside,thebrainis
protectedby3meningesnamelyouterDuramater,middleArachnoidmaterandinner
Piamater.ThespaceinbetweenarachnoidmaterandpiamateriscalledSub-arachnoid
spacefilledwithcerebrospinalfluid.Attheendoffourthweekoftheembryonicperiod,the
braindevelopsfrom3rudimentaryregionsoftheembryocalledprimarybrainvesicles.
Theyare-Prosencephalon,MesencephalonandRhombencephalon.
ProsencephalonorForebrainisfurtherdividedintoTelencephalonandDiencephalon.
Telencephaloncomprisesofcerebralhemispheres,hippocampus,amygdalaetcand
Diencephaloncomprisesofthalamus,hypothalamus,epithalamusandsubthalamus.
MesencephalonisotherwiseknownasMidbrainandisnotdivided.
RhombencephalonorhindbrainisdividedintoMetencephalonandMylencephalon.
MetencephaloncomprisesoftheponsandcerebellumandMylencephaloncomprisesofthe
medullaoblongata.Themedulla,ponsandmidbrainformsthebrainstem.Allthecranial
nervesaresituatedinthebrainstem.
CEREBELLUM
Itliesdorsaltothebrainstemandoneachside.Itisconnectedtothebrainstemby
3peduncles:
1.Inferiorcerebellarpeduncletothemedulla.
2.Middlecerebellarpeduncletothepons.
3.Superiorcerebellarpeduncletothemidbrain.
Anatomically,thecerebellumisdividedinto2largelaterallyplacedcerebellar
hemispheresandasmallmedialportioncalledvermis.
Functionally,cerebellumisdividedinto3partsaccordingtotheconnectionsthey
makewiththeothercomponentsofthemotorcontrolsystemas:
1.Vestibulocerebellum-relatedtothevestibularapparatusandconcernedwiththecontrol
ofbodypostureandequilibrium.
2.Spinocerebellum-receivesinformationfromthespinalcord,occupiesthemedialportion
ofthecerebellumandreceivesproprioceptiveinputfromthebody.Itisconcernedwith
thecontrolofaxial(trunk)andlimbmusclesandposturalreflexes.
3.Neocerebellum-receivesinformationfromthecerebralcortexandponsandisconcerned

8. withskilledvoluntarymovements.
FUNCTIONSOFCEREBELLUM:
1.Controlofbodypostureandequilibrium-Thevestibulocerebellumisconcernedwiththe
controlofbodypostureandequilibrium.Afferentsfromthevestibularapparatuspass
directlytothisportionofcerebellum.
2.Controlofmuscletoneandstretchreflex
3.Controlofmovements-Thecerebellumdoesnotinitiatemovements;insteadit
coordinatesmovementsthatareinitiatedinthemotorsystem.Itcontrolsthe
involuntaryandvoluntarymovements.
CEREBELLARDISEASE(CEREBELLARLESION)
Thecerebellarlesionofonehemisphereproducesdysfunctiononthesamesideof
thebody.Lesionsofcerebellarcortexcausemovementabnormalitieswhichgradually
disappearascompensationoccurs.Damagetotheneocerebellumcausesmostofthe
dysfunctionoroftheclinicalcerebellardiseaseinmansinceitformsabulkofthetotal
massoftheorgan.
Characteristicfeatures:-
1.Disturbanceinposture
a.Atoniaorhypotonia:Themuscletoneiseithercompletelylostormarkedlydecreasedon
theaffectedside.Therefore,themusclesfeelsoft(orloose)andthelimbmovestoandfro
freely.
b.Attitude:Thebodyweightisthrowntothehealthylegsothetrunkisbentwiththe
concavitytowardstheaffectedside.
c.Nystagmus:Itisthetremoroftheeyeballswhichoccurswhenthepatientattemptsto
fixhiseyesonanobject.
d.Deepreflexes:Thedeepreflexesbecomeweakandpendular.Thisisduetohypotoniaof
themuscles.
2.Disturbancesofvoluntarymovement
a.Asthenia:Itisthefeeblenessofmovements.Themusclestirereadily,therefore,
voluntarymovementsarecarriedoutslowly.
b.Ataxia:itistheincoordinationofmovements
3.Intentiontremor-Itisacommonremarkablefeatureofcerebellarlesions.Such
patientscannotperformmovementssmoothly.Thistremoroccurswhenthepatient

9. triestodoawork;theirmovementsarejerkyandaccompaniedbyoscillatingtoand
fromotionswhileperformingthatwork.Thetremorsarecoarseandcanbeclearly
seenwhenthepartisusedinavoluntarymovement.
4.Gait-Thepatientwalksawkwardlywiththefeetwellapart.Theyhavesuch
difficultymaintainingbalancethattheirgaitappearsdrunken,socalledDrunkenGait.
Thepatientwalksinazig-zagmanneranddeviatestotheaffectedsidedueto
hypotonia.
5.Speech-Itisslowandlalling(likeababy).
BASALGANGLIA
Thetermbasalgangliaisappliedtoagroupofnuclei(massofgraymatter)intheforebrain
andupperpartofthebrainstemthathavemotorfunctionofgreatimportance.Itincludes
CorpusstriatumcontainingCaudatenucleusandLenticularnucleuswhichcomprisesof2
othernucleinamelyPutamenandGlobuspallidus,SubthalamicnucleusandSubstantianigra.
FUNCTIONSOFBASALGANGLIA:
1.ThebasalgangliaisinvolvedinthePlanningandprogrammingofmovementsinthe
processesbywhichanideaofvoluntarymovementisconvertedintotheprecise
action.
2.Theactivityofbasalgangliaincreasesduringslow,steadydampmovementandis
silentduringrapidmovement.
3.Thebasalgangliainhibitsthestretchreflex(muscletone)throughoutthebodyby
stimulationofthecaudatenucleus.Thisiswhydamagetothebasalganglia
producesrigidity.
4.Itregulatesthesubconsciousgrossmovementsoccurringingroupsofmuscles.
5.Thecaudatenucleusplaysanimportantroleincognitiveprocesses.
6.Theglobuspallidusprovidesappropriatemuscletoneforperformanceofskilled
movements.
7.Thesubstantianigraiscenterforcoordinationofthoseimpulseswhichareessential
forskilledmovements.
8.Thebasalgangliaisresponsibleforcontrolofnormalautomaticandassociated
movementssuchasswingingofarmswhilewalking.
PARKINSON'SDISEASE
Parkinson'sdiseaseistheslowlyprogressivedegenerativediseaseofnervoussystem

10. associatedwithdestructionofbraincellsproducingdopamine.Itiscauseddueto
destructionofsubstantianigraandnigrostriatalpathway.ItisalsocalledParkinsonismor
paralysisagitans(shakingpalsy).ThesignsandsymptomsofParkinson'sdiseaseis
collectivelycalled“TRAP”-Tremor,Rigidity,AkinesiaandPosturaldefects.
1.Tremor-consistsofregular,rhythmic,alternatecontractionofthemuscles.Its
frequentpresencecnbeseenasPill-rollingmovementsi.e.rhythmiccontractionof
thethumboverfirst2fingers.Commonsitesarefingers,hands,lipsortongueand
oftenitcausesmovementsofpronationandsupination.Itispresentatrestbut
disappearsduringactivity,thereforepopularlycalledasrestingtremor.Itincreases
inemotionalstates,excitementoranxietyduetosecretionofepinephrinefromthe
adrenalmedulla,whichinturnexcitestheRAS.However,thetremordisappears
duringsleepduetodecreasedactivityoftheRAS.
2.Rigidity-stiffnessofthemusclesduetoincreasedmuscletone.Itaffectsmainly
largeproximalgroupofmusclesofthelimbs.Inadvancedcases,asaresultof
markedrigidity,statuelikestateisproducedandbothvoluntaryandinvoluntary
movementsbecomeprogressivelymoredifficult.
3.Akinesia-weaknessorpovertyofmovements.Itleadstodifficultyininitiating
movements,slowandmonotonousspeech,defectsinmovementofexpression,the
facebecomesmask-like,lossofnormalsubconsciousassociatedmovements;
thereforenoswingingofarmsoccursduringwalking.
4.Posturaldefects-Stoopingofthebody,quickwithshortsteps.
5.Emotionalandspeechproblems;dementia.
THALAMUS
Thalamusisalargeovoidmassofgraymatter,situatedbilaterallyinthediencephalon.
Itisamajorrelaystation.Allgeneralandspecialsensationsexceptsmellandafferent
impulsesfromtheRASsynapsehere.
FunctionsofThalamus
1.Thethalamusisagreatsensoryrelaystationandintegratingcenterformostinputs
beforerelayingthemtothecerebralcortex.Forex:relaystationinthepathwayof
somestheticsensationscomingfromtheoppositehalfofthebody;relaystationfor
theimpulsescomingfromoppositecerebellumontheirwaytothemotorcortex;relay
stationfortheimpulsescomingfromthereticularformation;relaystationinthe

11. auditoryandvisualpathways;relaystationforautonomicandemotionalreactions
duetotheitsconnectionswiththehypothalamusandlimbicsystem.
2.ItisresponsibleformaintainingconsciousandalteringresponsesofRAS.
3.Itisresponsibleforthesubcorticalperceptionofsensations.Perceptionof
sensationstosomeextentispossiblewithoutthesensorycortex.
4.Itisconcernedwithcontrolofmuscularmovementsviaitsvariousconnectionswith
thebasalganglia,cerebellumandmotorcortex.
5.Itisanintegratingcenterforsleep.
6.Itisconcernedwithrecentmemoryandemotion.
7.Itisconcernedwithlanguage(speech)function.
8.ItplaysanimportantroleingenesisofEEG.
HYPOTHALAMUS
Thehypothalamuswhichliesbelowthethalamusisseparatedfromthalamusby
hypothalamicsulcus.
FunctionsofHypothalamus
1.Regulationofbodytemperature-hypothalamusplaysanimportantroleinthe
integratedcontrolofheatproductionandheatlossfromthebody.
2.Regulationofanteriorpituitaryglandactivity-regulatestheactivityoftheanterior
pituitarythroughthereleaseofreleasingfactorsandrelease-inhibitingfactors.
3.Regulationofposteriorpituitaryhormonesecretion.
4.Controlofcircadianrhythm-Thereisacircadianrhythmordiurnalvariationformany
bodyfunctions,whichisabout24hours.
5.Controlofsleep-wakingcycle
6.ControloftheANS-ThehypothalamusiscalledtheheadganglionofANS.For
example-stimulationoftheanteriorhypothalamuscausesparasympatheticresponse
likecontractionoftheurinarybladder;stimulationofthelateralareasofthe
hypothalamusproducessympatheticresponseslikeriseinBP,pupillarydilationetc.
7.Controlofhungerandfeeding-Foodintakeisregulatedby2centerspresentinthe
hypothalamus;feedingcenterandsatietycenter.
8.Regulationofwaterbalance-hypothalamusregulateswatercontentofthebodyby2
mechanisms-thirstmechanismandADHmechanism.
9.Roleinemotionalandbehavioralchanges

12. 10.Regulationofsexualfunction,responsetosmell.
CEREBRALCORTEX
Thecerebralcortexisalsocalledpallidumanditconsistsof2hemispheres.The2
cerebralhemispheresareseparatedbyadeepverticalfissure.Theseparationiscomplete
anteriorlyandposteriorly.Butinthemiddleportion,thefissureextendsonlyuptocorpus
callosum.Corpuscallosumisabroadbandofcommissuralfibers,connectingthe2
hemispheres.Thesurfaceofthecerebralcortexischaracterizedbycomplicatedpatternof
sulci(singular-sulcus)andgyri(gyrus).Sulcusisaslightdepressionorgrooveandgyrus
isaraisedridge.Thesulciandgyridivideeachcerebralhemisphereinto4lobes.The
lobesare-Frontallobe,Parietallobe,OccipitallobeandTemporallobe.
The2cerebralhemispheresarenotfunctionallyequivalent.Morethan90%ofthe
individualsarerighthanded.Intheseindividuals,thelefthemisphereisdominantandit
controlstheanalyticalprocessandlanguagerelatedfunctionssuchasspeech,readingand
writing.Hence,thelefthemisphereofthesepersonsiscalleddominantorcategorical
hemisphere.Therighthemisphereisalsocalledrepresentationalhemispheresinceitis
associatedwithartisticandvisuo-spatialfunctionslikejudgingthedistance,determining
thedirection,recognizingthetonesetc.Lesioninthedominanthemisphereleadsto
languagedisordersandlesionintherepresentationalhemispherecausesonlymildeffects.
Broadmanndividedeachofthecerebralhemisphereintoseveralareascalled
Broadmann’sareas.Eachcerebralhemispherecontainsatotalof47areas.Theseareas
wereoriginallynumberedseparatelythinkingthateachareahasanabsolutelyselective
function.Afewimportantareaswiththeirnumbersareasfollows:
1.Areas3,1,2:PrimarySomatosensory(somasthetic)areaintheParietallobe.
2.Area4:PrimarymotorareaintheFrontallobe.
3.Area6:Premotorareainthefrontallobe.
4.Areas5,7:Somatosensoryassociationareaintheparietallobe.
5.Area8:Frontaleyefieldinthefrontallobe.
6.Area17:PrimaryVisualareaintheoccipitallobe.
7.Area18:Visualassociationareaintheoccipitallobe
8.Area19:Occipitaleyefield.
9.Area22:AuditopsychicareaorWernicke’sarea(concernedwiththeinterpretation
ofauditorysensation).

13. 10.Areas41,42:Primaryauditoryarea(concernedwithperceptionofauditory
impulses,analysisofpitchanddeterminationofintensityandsourceofsound).
11.Areas44,45:Broca’sareaormotorareaforspeech.
LIMBICSYSTEM
Limbicsystemisacomplexsystemofcorticalandsubcorticalstructuresthatforma
ringaroundthehilusofcerebralhemisphere.Limbicsystemisoneoftheoldestpartsof
thebrainandisrelatedtoolfactorylobe.Itisprimarilyrelatedtoemotionalpartofourlife
andisextensivelyconcernedwithmemory.
FunctionsofLimbicsystem:
1.Olfaction-Thepyriformcortexandamygdaloidnucleusformtheolfactorycenters.
2.Regulationofendocrineglands-Hypothalamusplaysanimportantroleintheregulationof
endocrinesecretions.
3.Regulationofautonomicfunctions-Hypothalamusplaysanimportantroleinthe
regulationofautonomicfunctionssuchasheartrate,BP,waterbalance,bodytemperature
etc.
4.Regulationoffoodintake-Alongwithamygdaloidcomplex,thefeedingcenterandsatiety
centerpresentinthehypothalamusregulatefoodintake.
5.Controlofcircadianrhythm-Hypothalamusistakingamajorroleinthecircadian

14. fluctuationsofvariousphysiologicalactivities.
6.Regulationofsexualfunction-hypothalamusisresponsibleformaintainingsexual
functions.
7.Roleinemotionalstate-Theemotionalstateofhumanbeingsismaintainedbythe
hippocampusalongwithhypothalamus.
8.Roleinmemory-HippocampusandPapezcircuitplayanimportantroleinmemory.
9.Roleinmotivation-Rewardandpunishmentcenterspresentinthehypothalamusand
otherstructuresoflimbicsystemareresponsibleformotivationandthebehaviorpatternof
humanbeings.
CEREBROSPINALFLUID(CSF)
CSFisaclear,colorlessandtransparentfluidthatcirculatesthroughventriclesof
brain,subarachnoidspaceandcentralcanalofthespinalcord.ItisapartofECF.The
normalvolumeofCSFisabout150mLanditvariesbetween100and200mL.
Ventriclesofthebrainareseriesofinterconnectedchamberswithinthebrain.Theyare:
1.2Lateralventricles,oneineachcerebralhemisphere
2.3
rd
ventricleinthemidbrainwhichcommunicateswiththelateralventriclesby
ForamenofMonroandbelowwiththe4
th
ventriclebyAqueductofSylvius
3.4
th
ventriclethatliesinbetweenponsandmedulla.
PropertiesandcompositionofCSF:
Properties:Volume:150mL
Rateofformation:0.3mL/minute
Specificgravity:1.005
Reaction:Alkaline
Composition:
AsCSFisapartoftheECF,itcontainsmoreamountofsodiumthanpotassium.
CSFalsocontainssomelymphocytes.TheCSFsecretedbytheventricledoesnotcontain
anycell.Thelymphocytesareaddedwhenitflowsthroughthespinalcord.
CSF
LymphocytesinCSF:
6/cu.mm

15. Water-99.13% Solids-0.87%
Organicsubstances Inorganicsubstances
Proteins,aminoacids,sugar, Na,K,Ca,Mg,Cl,
Phosphate,
Cholesterol,urea,uricacid, Bicarbonates,sulfates.
Creatinine,lacticacid.
FORMATIONOFCSF
CSFisfromedbythechoroidplexusessituatedwithintheventricles.Thechoroids
plexusesareatuftofcapillaryprojectionspresentinsidetheventriclesandarecoveredby
piamaterandependymalcovering.AlargeamountofCSFisformedinlateralventricles.
CSFisformedbytheprocessofsecretion.TheformationofCSFdoesnotinvolve
ultrafiltrationordialysis.Ontheotherhand,withtheexpenditureofenergy,activetransport
mechanismisinvolvedinthesecretion.
CIRCULATIONOFCSF
MajorquantityofCSFisformedinthelateralventriclesandpassesthroughthe
foramenofMonrointothe3
rd
ventricle.Fromhere,itpassestothe4
th
ventriclethroughthe
aqueductofSylvius.Fromhere,itentersthecisternamagnaandcisternalateralisthrough
foramenofMagendieandforamenofLuschka.Aportionofthecisternalfluidcirculates
throughthespinalsubarachnoidspace.Thegreaterpartofthefluidpassesupwardsover
thebrainstemtothesurfaceofcerebralhemispheres.
PressureexertedbyCSFinmanvariesindifferentpositions:
Lateralposition=10-18cmofH2O
Lyingposition=13cmofH2O
Sittingposition=30cmofH2O
Certaineventslikecoughingandcryingincreasethepressurebydecreasingtheabsorption.
CompressionoftheinternaljugularveinalsoraisestheCSFpressure.
FUNCTIONSOFCSF:
1.Protectivefunction-CSFactsasafluidbufferandprotectsthebrainfromshock.Since
thespecificgravityofbrainandCSFismoreorlessthesame,brainfloatsinCSF.When
headreceivesablow,CSFactslikeacushionandpreventsthemovementofbrainagainst
theskullboneandtherebypreventsthedamageofbrain.

16. 2.Regulationofcranialcontentvolume-regulationofcranialcontentisessentialbecause,if
thecranialcontentsincreaseinvolume,thereisincreaseintheabsorptionofsubstances
intothevenoussinuses.Ithappensincasesofcerebralhemorrhageandtumorsinthe
brain.
3.Mediumofexchange-CSFisthemediumthroughwhichmanysubstancesparticularlythe
nutritivesubstancesandwastematerialsareexchangedbetweenbloodandbraintissues.
COLLECTIONOFCSF
Lumbarpuncture-Postureofbodyforlumbarpuncture
Therecliningbodyisbentforward,soastoflexthevertebralcolumnasfaras
possible.Thenthebodyisbroughtneartheedgeofatable.Thehighestpointoftheiliac
crestisdeterminedbythepalpation.Alineisdrawnonthebackofthesubjectbyjoining
thehighestpointsoftheiliaccrestsofbothsides.Oppositethelidplane,thislinecrosses
the4
th
lumbarspine.Afterdeterminingtheareaof4
th
lumbarspine,the3
rd
lumbarspineis
palpated.Andtheneedleisintroducedthroughthesofttissuespacebetweenthe2spines
sothattheneedlereachesthesubarachnoidspace.
Reasonsforselectingthissite:
1.Thespinalcordwillnotbeinjured,becauseitterminatesbelowthelowerborderof
the1
st
lumbarvertebra.Thecaudaequinemaybedamaged.Evenifitisinjured,it
isregenerated.
2.Thesubarachnoidspaceiswiderinthissite.Itisbecausethepiamaterisreduced
verymuch.
BLOOD-BRAINBARRIER
Bloodbrainbarrierisaneuroprotectivestructurethatpreventsentryofmany
substancesandpathogensintothebraintissuesfromblood.Itwasobservedmorethan
50yearsago,thatwhentrypanblue,theacidicdyewasinjectedintolivinganimals,all
tissuesofthebodywerestainedbyitexceptthebrainandspinalcord.Thisobservation
suggestedthattherewasahypotheticalbarrier,whichpreventedthediffusionoftrypanblue
intothebraintissuesfromcapillaries.ThisbarrierwasnameastheBlood-BrainBarrier.
Thebarrierexistsinthecapillarymembraneofallpartsofthebrainexceptinsomeareasof
hypothalamus.Thetightjunctionsoftheendothelialcellsofthebrainareresponsiblefor
theBBBmechanism.BBBactsasbothamechanicalbarrierandatransportmechanism.
Itpreventspotentiallyharmfulchemicalsubstancesandpermitsmetabolicandessential

17. materialsintothebraintissues.Bypreventinginjuriousmaterialsandorganisms,BBB
provideshealthyenvironmentsforthenervecellsofthebrain.
SubstanceswhichcanpassthroughtheBBBinclude-oxygen,carbondioxide,water,glucose,
aminoacids,electrolytes,drugssuchasL-dopa,tetracyclineandmanylipidsolubledrugs,
anestheticgasessuchasether,nitrousoxidewhicharelipidsolubleandotherlipidsoluble
substances.
SubstanceswhichcannotpasstheBBBinclude-injuriouschemicalagents,pathogenslike
bacteria,drugssuchaspenicillinandthecatecholamines(Dopaminealsocannotpass
throughBBB.SoParkinsonismistreatedwithL-dopainsteadofdopamine),bilepigments
(howeversincethebarrierisnotwelldevelopedininfants,thebilepigmentsenterthebrain
tissues.Duringjaundiceininfants,thebilepigmentsenterthebrainandcausesdamageto
thebasalganglialeadingtokernicterus).
SPINALCORD
Spinalcordisthemainpathwayconnectingthebrainandtheperipheralnervous
system.Itextendsdownthespacebetweenthefirstandsecondlumbarvertebrae.The
coveringsofthespinalcordarethesameasthatofthebrain-meninges.Thelengthof
spinalcordinmalesis45cmandinfemalesis43cm.Spinalcordisdividedinto31
segments.Theyare-Cervical-8;Thoracic-12;Lumbar-5;Sacral-5andCoccygeal-1.
Belowthelumbarvertebra,thespinalcordnarrowsrapidlytoaconeshapedtermination
calledConusmedullaris.Thepiamaterextendsbelowtheconusmedullarisasthefilum
terminalewhichanchorsthespinalcordtothecoccyx.Acollectionofnervesfibers
continuetotravelbelowtheconusmedullarisandarecalledCaudaequina.Spinalcord
helpsinthetransmissionofimpulsesbetweenthebrainandrestofthebodyandcontrols
numerousreflexes.
Ontheanteriorsurfaceofthespinalcord,thereisadeepfissureknownasthe
anteriormedialfissure.Inthemiddleofthespinalcordgraymatter,thereisasmall
openingcalledthespinalcanalthroughwhichtheCSFflows.Inthespinalcord,thegray
matterisseeninsideandwhitematteroutside.Graymatterofthespinalcordisa
collectionofnervecellbodies,dendritesandpartsofaxons.Itisplacedcentrallyinthe
formofwingsofabutterflyanditresemblestheletter‘H’.Graymattercontains2typesof
multipolarneurons,GolgiTypeIneurons(havinglongaxonsandusuallyfoundintheanterior
hornsformingthelongtractsofspinalcord)andGolgiTypeIIneurons(havingshortaxons

18. andfoundmostlyinposteriorhorns).Thegraymatterofspinalcordisorganizedin2
methods-NucleiorcolumnsandLaminaeorlayers.Whitematterofthespinalcord
surroundsthegraymatter.Itisformedbythebundlesofbothmyelinatedandumyelinated
fibers,butpredominantlythemyelinatedfibers.Thenerverootsofthespinalcorddivide
thewhitematterinto3columnsnamely-Anteriororventralwhitecolumn,Lateralwhite
columnandPosteriorordorsalwhitecolumn.
Thesegmentsofthespinalcordcorrespondtothe31pairsofspinalnervesina
symmetricalmanner.Eachspinalnerveisformedbyandanteriororventralandaposterior
ordorsalroot.
Functionsofspinalcord:
ItactsasanimportantpartofCNS.
Sensorypathwaysareorganizedinthespinalcordandmotorimpulsesfromthebrain
comesdownthroughthemotorpathwayssituatedinthespinalcordandreachesthe
muscles.
Itactascentreforanumberofreflexeslikekneejerk,withdrawalreflexandposturalreflex.
Itincludesthevisceralfunctionslikebreathing,urination,defecationandsexualfunctionsin
male.
VasomotorfunctiontakesinthesegmentsofT11–L3.Thespinalcordcontrolsvasomotion,
sweatingandpiloerection.
REFLEXACTIVITY
Reflexactivityistheresponsetoaperipheralnervousstimulationthatoccurswithout
oconsciousness.Itisatypeoprotectivemechanismanditprotectsourbodyfrom
irritabledamages.Forex:Whenahandisplacedonahotobject,itiswithdrawn
immediately.Whenaverybrightlightisthrownintotheeyes,eyelidsareclosedandpupil
isconstrictedtopreventthedamageofretinabytheentranceofexcessivelightintothe
eyes.
REFLEXARC
Thepaththroughwhichreflexactiontakesplaceisknownasreflexarci.e.itisthe
anatomicalnervouspathwayforareflexaction.Asimplereflexarcincludesfive
components.
1.RECEPTOR:ItItheendorgan,whichreceivesthestimulus.Whenthereceptoris
stimulated,impulsesaregeneratedinafferentnerve.

19. 2.AFFERENTNERVE:Afferentorsensorynervetransmitssensoryimpulsesfromthe
receptortothecenter.
3.CENTER:Thecenterreceivesthesensoryimpulsesviaafferentnervefibersandin
turn,itgeneratesappropriatemotorimpulses.Thecenterislocatedinthebrain
orspinalcord.
4.EFFERENTNERVE:Efferentormotornervetransmitsmotorimpulsesfromthe
centertotheeffectororgan.
5.EFFECTORORGAN:Theeffectororganisthestructuresuchasthemuscleor
glandwheretheactivityoccursinresponsetothestimulus.
Afferentandefferentnervefibersmaybeconnecteddirectlytothecenter.In
someplaces,oneormoreneuronsareinterposedbetweenthesenervefibersand
thecenter.
Suchneuronsarecalledconnectorneuronsorinterneurons.
CLASSIFICATIONOFREFLEXES
Reflexesareclassifiedbyfivedifferentmethodsdependinguponvariousfactorasgiven
below:
I. Whetherinbornoracquired
II.Situationofthecenter
III.Purposeorfunctionalsignificance
IV.Numberofsynapse
V. Clinicalbasis.
I. DEPENDINGUPONWHETHERINBORNORACQUIRED
1.UnconditionedreflexesorInbornreflexes:Unconditionedreflexesareneuralreflexes
whicharepresentsincethetimeofbirthhencethenameinbornreflexes.Such

20. reflexesdonotrequirepreviouslearning,training,orconditioning.Thebestexample
isthesecretionofsalivawhenadropofhoneyiskeptinthemouthofanewborn
babyforthefirsttime.Thebabydoesnotknowthetasteofthehoneystillsalivais
secreted.
2.ConditionedreflexesorAcquiredreflexes:Conditionedreflexesarethereflexesthat
aredevelopedafterconditioningortraining.Thesereflexesarenotinbornbut
acquiredafterbirth.Suchreflexesneedpreviouslearning,training,orconditioning.
Theexampleisthesecretionofsalivabythesecretionofsalivabythesight,smell,
thoughtorhearingofaknownediblesubstance.
II.DEPENDINGUPONTHESITUATIONOFTHECENTER
1.Cerebellarreflex:Cerebellarreflexesarethereflexeswhichhavethecenterin
cerebellum.
2.Corticalreflexes:Corticalreflexesarethereflexesthathavethecenterin
cerebralcortex.
3.Midbrainreflexes:Midbrainreflexesarethereflexeswhichhavethecenter
inmidbain.
4.Bulbarormedullaryreflexes:Thesearethereflexeswhichhavethecenter
inmedullaoblongata.
5.Spinalreflexes:Reflexeshavingtheircenterinspinalcordarecalledspinal
reflexes.Dependinguponthesegmentsinvolved,thespinalreflexesare
dividedinto3groups:
a.Segmentalspinalreflexes
b.Intrasegmentalspinalreflexes
c.Suprasegmentalspinalreflexes.
III.DEPENDINGUPONTHEPURPOSEORFUNCTIONALSIGNIFICANCE
1.Protectivereflexesorflexionreflexes:Theprotectivereflexesarethe
reflexeswhichprotectthebodyfromnociceptic(harmful)stimuli.These
reflexesarealsocalledwithdrawalreflexesorflexorreflexes.Protective
reflexesinvolveflexionatdifferentjointshencethenameflexorreflexes.
2.AntigravityreflexesorExtensorreflexes:Thesearethereflexesthatprotect
thebodyagainstthegravitationalforce.Thesereflexesarealsocalledthe
extensorreflexesbecause,theextensormusclescontractduringthese

21. reflexesresultinginextensionatjoints.
IV.DEPENDINGUPONTHENUMBEROFSYNAPSE
1.Monosynapticreflexes:Reflexeshavingonlyonesynapseinthereflexarcare
calledmonosynapticreflexes.Stretchreflexisthebestexampleformonosynapticreflex
anditiselicitedduetothestimulationofthemusclespindle.
2.Polysynapticreflexes:Reflexeshavingmorethanonesynapseinthereflexarcare
calledpolysynapticreflexes.
V.DEPENDINGUPONCLINICALBASIS
Inclinicalpractice,thereflexesareclassifiedinto4types.
Superficialreflexes(Mucousmembranereflex:Ex.Cornealreflex,Cutaneousreflex:Ex.
Plantarreflex)
Deepreflexes(Ex.Kneejerkreflex)
Visceralreflexes(Ex.Pupillaryreflex)
Pathologicalreflexes(Ex.Babinski’ssign:Agentlescratchovertheouteredgeofthe
soleofthefootcausesdorsiflexionofgreattoeandfanningofothertoes.)
NerveTracts:
Nervetractisabundleofnervefiberscarryingsensoryormotorimpulsesfromonepartof
theCNStoanotherpart.Thetractsarebroadlyclassifiedinto3types.
AscendingTracts:theseareorganizedin3differentcolumnsofspinalcord.Theyare,
Posteriorcolumn,LateralcolumnandAnteriorcolumn.
PHYSIOLOGYOFPAIN
Painisdefinedasunpleasantexperienceassociatedwithorwithoutactualtissue
damage.Itisproducedbyrealorpotentialinjurytothebody.Oftenitisexpressed
intermsofinjury.Forexample,painproducedbyseveresustainedcontractionof
skeletalmusclesisexpressedascramps.Painmaybeacuteorchronic.Acute
painissharppainofshortdurationeasilyundefinedcause.Oftenitislocalizedina
smallareabeforespreadingtoneighboringareas.Usuallyitistreatedby
medications.Chronicpainistheintermittentorconstantpainwithdifferent
intensities.Itlastsforlongerperiods.Itissomewhatdifficulttotreatchronicpain
anditneedsprofessionalexpertcare.
COMPONENTSOFPAINSENSATION
Apainstimulusproducestwopainsensations

22. Fastpain
Slowpain.
Fastpainisthefirstsensationwheneverapainstimulusisapplied.Itisexperiencedas
abright,sharpandlocalizedpainsensation.Thefastpainisfollowedbytheslow
painwhichisexperiencedasadull,diffusedandunpleasantpain.
Thereceptorsforboththecomponentsforpainarethesame,i.e.thefreenerveendings.
But,theafferentnervefibersaredifferent.ThefastpainiscarriedoutbyAδfibers
andtheslowpainsensationiscarriedoutbyCtypeofnervefibers.
LateralSpinothalamictract:
Thefibersofthistractcarryimpulsesofpain
andtemperature.Thistractisformedbyfibersfrom
thesecondorderneuronsofthepathwayforthe
sensationsofpainandtemperature.Thistractis
situatedinthelateralfuniculustowardsmedialside.
Origin:Thefibersofthelateralspinothalamictract
takeoriginfromsubstantiagelatinosaofRolando
formthesecondorderneuronofthepainand
temperaturepathway.Theaxonsfromthesecond
orderneuronsmostlycrosstotheoppositesideand
reachthelateralcolumnofsamesegment.Few
fibersmayascendoneortwosegments,thencross
totheoppositeside,andascendinthelateral
column.Allthefiberspassthroughmedulla,pons
andmidbrainandreachthalamusalongwiththe
fibersofanteriorspinothalamictract.Someofthe
fibersoflateralspinothalamictractformcollaterals
andreachthereticularformationofbrainstem.The
fibersoflateralspinothalamictractformspinal
lemniscusalongwiththefibersofanterior
spinothalamictractatthelowerpartofthemedulla.
Thefibersoflateralspinothalamictract
terminateintheventralpostero-lateralnucleusof
thalamusalongwithanteriorspinothalamictract
fibers.Fromhere,3
rd
orderneuronfibersrelayto

23. PyramidalSystem:
Itincludesthedescendingpathwaysfromthecerebralcortextothebrainstemand
spinalcord.Thistractgoingtospinalcordformtwopyramidalstructuresinthemedullaon
eithersideofthemidline,henceitnamedaspyramidalsystem.Theotheroriginofthe
nameisthepyramidalcellsofthemotorcortexbutthesecellscontributeonlyaverysmall
numberofthefibers.Thesefibersactuallyinclude
Corticospinal
Corticonuclear
Othercorticobulbarfibers.
CorticospinalPathway:Thispathwaywhichextendsfromthecerebralcortextothespinal
cordisnamedascortico–spinalpathway.
Origin:Theprimarymotorareawhichhasthemostimportantcontributiontothetractbut
only2–4%ofthefibersoriginatefromthegiantpyramidalcellsofbetzinthisarea.
Course:Thistract,afteroriginatinginthecortexmovethroughthecerebralhemisphereto
thebrainstemandhencetothespinalcordasfollows:
1.Incerebralhemisphere:Thefibersarecontributedbydifferentpartsofthecerebral
cortex,theoriginofthetractisspreadwidely.Thefanshapedarrangementofthefibers
comingdownfromthecortexiscalledCoronaradiata.
2.IninternalCapsule:Itisacompressedbandoffiberswhichconnectsthecerebral
cortexhemispherewithotherpartsoftheCNS.Itissituatedbetweenthethalamus,and
theheadofthecaudatenucleusmediallyandlentiformnucleuslaterally.
3.Inmidbrain:Theheadofthefibersoccupymediallyandlagsarelaterally.
4.Inpons:Fiberspassingthroughthebasilarpartofthepons.
5.Inmedulla:Lowerborderofponsallthefibersreuniteagaintoformacompactbandto
producethemedullarypyramids,whichoccupytheupperhalfofthemedulla.Inthelower
partofthemedullafibersdecussatewiththefibersoftheoppositesideformingthe
pyramidaldecussation.
6.Inspinalcord:Fibersreunitetodifferenttractsanddescendthroughthespinalcord.
Termination:Corticospinalfibersterminateinthefollowingway:
1.Thelateralcorticospinalfibersenddirectlyonthemotorneuronessituatedlaterallyin
theanteriorgreycolumnandalsoonthenearbyinterneurones.
2.Anteriorcorticospinaltractfibersendmainlyviainterneuronesonthemedialgroupof

24. motorneuronesofanteriorhornofbothsides.
3.Theuncrossedlateralcorticospinaltractendonthesameside.
4.Fiberscomingfromthesensoryandotherpartsofparietalcortexmainlyendonthe
interneuronesintheposteriorgreycolumn.
Functionsofthepyramidalsystem:
4.Itisresponsibleforexecutionoftheskillfulvoluntarymovementsinvolvingthedistal
limbmusclesthroughthefibersendingsdirectlyonthealphamotorneurones.
5.Itinfluencesthestretchreflexesandalsothesensoryinputs.
6.Ithelpsinposturalmovementsbyitscontrolontheaxialmusles.
7.Thispathultimatelyinfluencesthemusclesbothviaalphaandgammamotorneurones.
Babinskisign:Itisasignofpyramidaltractlesion.Itmeansanextensorplantar
responsethatis,extensionofgreattoeandfanningoutoftheothertoeswhenthesoleof
thefootisscratched.Inbabies,thenormalplantarresponseisextensor.Thisisbecause
thepyramidaltractsarenotproperlydeveloped.Whenthebabylearnstowalk(15
th
-18
th
monthsofage)theplantarresponsebecomesflexor.
Extrapyramidalsystem:
Thedescendingfibersfromthebraintothespinalcord,exceptingtheseincludedin
thepyramidalsystem.Thetractsare:
1.Reticulospinal
2.Vestibulospinal
3.Rubrospinal
4.Tectospinal
Functions:
Itregulatesskeletalmuscletonebyinfluencingbothalphaandgammamotor
neurones.Itbringsaboutpatternsofactivity.Eg:-Flexorpattern,extensorpattern.Itis
responsibleforSynchronizationofmovements.Theextrapyramidalsystemperformsthe
grossposturalmovementstogetherwithmaintenanceofpostureandequilibrium.
UPPER&LOWERMOTORNEURONS:
Alltheneuronscontributingtothepyramidalandextrapyramidalsystemsshouldbe
calledUMN.Theanteriorhorncellsandtherelatedneuronsinthemotornucleiofsome
crainalnervesarecalledLMN.Thesearethelowestinpositioninthemotorsystemand
receiveallinputsfromhigherlevelandtransmitthesametothetargetorgans.Asallthe

25. impusesformotoractivityaretobefunneledintothemandthesearealsocalledFinal
Commonpath.
BROWN-SEQUARDSYNDROME
Itisanervousdisorderresultingfromthehemisectionofthespinalcord.
Causes:-
Brown-Sequardsyndromemaybecausedbyaspinalcordtumour,trauma(suchasa
gunshotwoundorpuncturewoundtotheneckorback),ischemia(obstructionofablood
vessel),orinfectiousorinflammatorydiseasessuchastuberculosis,ormultiplesclerosis.
Thesymptomsare:-
1.Atthesiteofinjury-Inthesamesideandoppositesideofthebody-severesensory
andmotorloss.
2.Abovethesiteofinjury-inthesameside;noserioussensoryormotorloss.
Theneuro-physiologicalchangestakingplacebelowthesiteofhemi-section
ofspinalcordisknownasBrownSequardsyndrome.Inthesamesidelossof
sensationlikefinetouch,vibration,touchdiscriminationetcbutsensationofpainand
temperaturemaybepresent.Intheoppositesidelossofpainandtemperature
sensation,verylittlemotorloss,finetouchsensationispresent.
PLEGIA
Plegiareferstoparalysisorstroke.
Monoplegia-Paralysisofanyoneofthe4limbs.
Hemiplegia-Paralysisofonesideofthebody.
Paraplegia-Paralysisofthelegs.
Quadriplegia-Paralysisofallthe4limbs.