neurology - bma your career... · neurology hollie wilson. ... other descending tracts to be aware...
TRANSCRIPT
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Neurology
Hollie Wilson
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Objectives
• Anatomy
• Physiology:• Functional centres of brain• UMN lesion vs. LMN lesion• Spinal cord
• Main tracts – ascending and descending• Nerve roots and peripheral nerves – action potentials
• Pathology
• Quiz
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Cortical Organisation
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Broca’s and Wernicke’s areas – speech and language
• Broca’s : frontal lobe• Expressive language
• Wernicke’s : temporal lobe• Receptive language
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Blood supply to the brain
AnteriorcerebralcirculationINTERNALCAROTIDARTERY
Posteriorcerebralcirculation2VERTEBRALARTERIES
RedundancyAnastomoticconnectionsfacilitatecollateralbloodsupplyintheeventofnarrowingorobstructionofavessel
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Threemainpairsofarteriesarising
fromcircleofWillis
•ACA•MCA•PCA
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Anterior Cerebral Artery Middle Cerebral Artery Posterior Cerebral Artery
Medial brain Lateral brain Lateral and Medial
Frontal lobe (primary motor cortex) Frontal lobe(Broca’s, primary motor cortex)
Occipital lobe (primary visual cortex)
Parietal lobe (primary somatosensory cortex)
Parietal lobe (primary somatosensory cortex)
Inferior temporal lobe
Superolateral temporal lobe (Wernicke’s area)
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Pastquestion1.Areaofbraincontrollingspeech?
• Frontallobeofdominanthemisphere
2.Location?• Broca’s area
3.Bloodsupply?• MCA
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Pastquestion
• Distinguishbetweendysarthriaanddysphasia?
• Dysarthriaisaspeechdisordercausedbydisturbanceofmuscularcontrolie aproblemwitharticulation
• Dysphasia/Aphasiaisanimpairmentoflanguageandmaybereceptiveorexpressive.• Expressive(Broca’s area)• Receptive(Wernicke’sarea)
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Stroke
• Aetiology• Ischaemic(85%)
• Thrombosis• Embolism• Hypoperfusion
• Haemorrhagic(15%)
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RiskfactorsModifiable• Hypertension• DM• AF• Smoking• Hyperlipidaemia
Non‐modifiable• Previousstroke/TIA• Increasingage• FH
ABCD2 score predicts risk of stroke following TIA
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Clinicalpresentation• Clinicalpresentationaccordingtovascularterritoryinvolved• MCAmostcommonlyaffectedvessel
• Contra‐lateralhemiparesis• Homonymoushemianopia• Dysphasia
• Clinical• History
• Timeofonset• Ix
• Bloodglucose• CTBrain
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Visualfielddefects1.CompletelossofvisionLeye(opticnervelesion)
2.Bitemporal hemianopia (opticchiasmlesion)
3.Righthomonymoushemianopia(optictractlesion)
4.Righthomonymoussuperiorquadrantanopia
5.Righthomonymousinferiorquadrantanopia
6.Righthomonymoushemianopiawithmacularsparing
Agoodworkingknowledgeofthevisualpathwayisimportanttoaidwiththelocalisationofcerebrallesionsfromclinicalfindingsalone.
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Upper motor neuron lesions vs. lower motor neuron lesions
• Anuppermotorneuronisamotorneuron,thathasit’scellbodyinthecerebralcortex,andsynapseswithlowermotorneuronsintheanteriorhorncellorcranialnervenuclei
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N.B.TheincreasedtoneandhyperreflexiadoesnotdevelopimmediatelyfollowingthedevelopmentofanUMNlesion,duetoaphenomenoncalledSpinalShock.Initiallythetoneandreflexeswillbereduced inanuppermotorneuronlesion.
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“Uppersparesupper”
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Story so far…
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SpinalCordTracts
Thespinalcordtractsruninthewhitematterofthespinalcord
Ascending Descending
FROM periphery TO brain
Mainly sensoryfeedback
FROM brainTO periphery
Mainly motorcontrol
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DescendingSpinalCordTracts
1. Corticospinal Tract (Pyramidal Tract)
Primary Motor Cortex
Internal capsule
Pons & Midbrain
Anterior horn of spinal cord
Crosses over at base of medulla
Other descending tracts to be aware of: 2. Vestibulospinal tract3. Tectospinal tract4. Reticulospinal tract
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Corticospinal Tract
• Originatesinthemotorcortex(cortico)andterminatesintheanteriorhorncellsofthespinalcord
• Passesthroughtheinternalcapsule,downthroughtheponsandmidbrain
• Crossesoveratthebaseofthemedulla andformsapyramidalbulgeontheanterioraspectofthemedulla(hencepyramidaltract).
• Fromhere,itdescendsinthelateralaspectofthecorticospinaltracttotheanteriorhornofthespinalcord,whereitsynapseswithmotorneurons
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Recap:ActionPotentials
K+ effluxNa+ influx
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ActionPotential1• Initiation
• Theintra‐cellularenvironmentoftheaxonisnormallynegativewithrespecttotheextra‐cellularenvironment(restingmembranepotential~‐70mV).
• Allornothingresponse– astimulusmustdecreasethispotential(inotherwordsmaketheinsideoftheaxonlessnegative)inordertobreachthethresholdpotential.
• Oncethethresholdpotentialisbreachedthisresultsinavoltage‐dependentrapidincreaseinmembranepermeabilitytoNa+.TheresultantinfluxofNa+ resultsindepolarisationwhichreversesthepotentialacrosstheneuronalcellmembrane(theinsideisnowtransientlypositiveandtheoutsidenegative).
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ActionPotential2
• Propagation• Actionpotentialstravelalonganaxonbysaltatory conduction
• GapsinthemyelinsheathformnodesofRanvier alongtheaxonwhichallowtheactionpotentialtojumpfromnodetonode
• Conductionvelocityisthereforeincreasedbymyelination andisalsoproportionaltotheaxondiameter.
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ActionPotential3• Repolarisation
• Thesamevoltage‐dependentincreasewhichfacilitatedNa+influxalsofacilitatesaslowerK+ efflux
• Thislossofpositivechargerestoresthenormalnegativerestingmembranepotential(repolarisation)
• Refractoryperiod– asecondstimulusduringthisperiodwillnotresultindepolarisationduetotransientinactivationofNa+ channels
K+ efflux
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ActionPotential4• Synaptictransmission
• Neuronsareconnectedfunctionallybysynapsesbetweentheaxonofoneneuroneandthedendritesofanother.
• Depolarisationofthepre‐synapticmembraneresultsinincreasedpermeabilitytoCa2+ bytheopeningofvoltage‐gatedCa2+ channels.
• SubsequentCa2+ influxcausesfusionofsynapticvesicleswiththepre‐synapticmembraneandneurotransmitterreleaseacrossthesynapticcleft.
• Bindingoftheneurotransmittertoreceptor‐operatedionchannelsonthepost‐synapticmembraneallowsexcitationorinhibitionofthepost‐synapticneurone.
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The Neuromuscular Junction
• Terminalboutonofnervefibres sitsininfolding ofsarcolemma(musclecellmembrane)calledajunctionalfold
• TheAcetycholinereceptorsfoundattheneuromuscularjunctionarenicotinicacetylcholinereceptors
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NeuromuscularTransmission1. Actionpotentialtravelsdowntheaxonoftheneuroninnervatingthemusclefibre,leadingtotheopeningof
VoltageGatedCalciumChannels2. ThisleadstoinfluxofCa 2+3. Byanunknownmechanism,theincreasedCa 2+causesbindingofvesiclescontainingacetylcholinetothe
pre‐synapticmembrane,causingreleaseofacetylcholineintothesynapticcleftviaaprocesscalledexocytosis
4. Thisacetylcholinebindstoacetycholine receptorsontransmittergatedionchannels,thatopeninresponsetothebindingofacetylcholine
5. ThiscausesNa+influxintothemusclefibre6. Thisdeplolarises themusclefibre,leadingtothegenerationofanactionpotentialwithinthemuscle.Thisis
knownasanexcitatorypost‐synapticpotentialorEPSP7. Inaprocessknowasexcitation‐contractioncoupling,theactionpotentialspreadstothesarcoplasmic
reticulumviaT‐tubules,andthearrivalofanactionpotentialtothesarcoplasmicreticulumleadstoCa2+releasefromtheorganelle.ThisCa2+bindstoTroponinC,andthisleadstoaconformationalchangethatmeansthattropomyosin movesawayfromitsnormalbindingsiteontheactinfilament,allowingthemyosinheadstobindtotheactinfilamentandcausemuscularcontraction
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SpinalCordTracts
Thespinalcordtractsruninthewhitematterofthespinalcord
Ascending Descending
FROM periphery TO brain
Mainly sensoryfeedback
FROM brainTO periphery
Mainly motorcontrol
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AscendingSpinalCordTracts
1. ThePosteriorColumn:finetouch,vibrationandproprioception.Thesetractscrossoverinthemedulla,beforeterminatinginthethalamus.Fromhere,neuronsleavethethalamustoascendintotheparietallobe(primarysomatosensorycortex)
2. TheSpinothalamicTract:anterior(crudetouch)andlateral(painandtemperature)
Thesetractscrossoveratthelevelofthespinalcordatwhichtheyenterthroughthedorsalhorn.Ascendinthespinalcordtoreachthethalamus,fromwherethereareprojectionstotheparietallobe
3. Thespinoreticular tracts4. Thespinocerebellartracts (unconsciousproprioception)
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AscendingSpinalCordTracts
Fine touchVibrationProprioception
Crude touchPainTemperature
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Question:
A 21 year old man was involved in a street fight and brought to ED. He sustained a knife wound to the left side of his neck which damaged his spinal cord unilaterally. What sensory and motor impairment will he have following this injury?
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Objectives
• Anatomy
• Physiology:• Functional centres of brain• UMN lesion vs. LMN lesion• Spinal cord
• Main tracts – ascending and descending• Nerve roots and peripheral nerves – action potentials
• Pathology: strokes, spinal cord damage
• Quiz
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QUIZ
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Additional notes
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SpinalReflexArc
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MuscleSpindle• Musclemechanoreceptorsthatdetectstretchingofmusclefibres
• Composedofintrafusal fibresthatruninparalleltoextrafusalfibres thatformthemusclebulk
• Acttoregulatemuscletoneandmediatetendonreflexes Action Potentials
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MuscleStretchvs MuscleTension
• Musclestretch:changeinlength ofamuscle(usuallyanincreaseinlength).Thisisdetectedbythemusclespindlethatlieswithinthemuscle.Spindlesalsodetecttheratethatthelengthofthemuscleischanging(dynamicinformation).
• Muscletension:weight/force appliedtotheendofamuscle,andisdetectedbytheGolgiTendonOrgan,thatlieswithinthemuscletendon.
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GolgiTendonOrgan• Alsoinvolvedinmuscleproprioception,butinsteadofsignallingchangesinmusclelength,theysignalchangesinmuscletension
• Unlikemusclespindles,the1bafferentfibres synapsewithinterneuronsinthespinalcord,thatinturnsynapsewithalphamotorneurones,toinhibit them
• Acttomediatetheforceofmusclecontraction‐i.e graspingapintglasshardenoughtostopitfalling,butnotsohardthattheglasssmashes
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GolgiTendonReflex