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N E U R O- M U S C U L A R SYS T EM : b as i c p r i n c i p l es

This text covers the fundamental principles of the neuro-muscular system, including excitability, electrical potential, synaptic modulation, muscle contraction mechanisms, motor unit control, and reflexes.

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N E U R O- M U S C U L A R SYS T EM : b as i c p r i n c i p l es

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  1. NEURO-MUSCULARSYSTEM:basicprinciples P.Kučera,FBMIKladno,winter2013 "…eveninMan,thecrownoflifeisnotthethoughtbuttheact…«(SirCharlesSherrington) Plán 1Základyexcitability,elektrofyziologie Electricalpotentialacrossthemembraneofexcitablecells:-atrest -afteractivation -ionicchannels -useoftheactionpotential -synapticmodulations 2Nervo-svalovýsystém Molecularmechanismsofmusclecontractionanditscontrol Rolesofthemotoract,complexityofmovements Neuralcommand:-motorprogram -organisation:hierarchy&cooperativity -motorunit -controlofmuscularforce Innervationandreceptorsofskeletalmuscles slide: 1 2 3 4 5 6,7 8 9 10,11 12,13 14 15 16 17,18 19,20 Spinalreflexes(exemples) -proprioceptive:myotatic&gammaloop -heteroceptive(nociceptive) -kinesthesia,labyrinth,vision -corticalorganisation&desceningpathways Posturalsense Voluntarymovement Organisationofpurposefulactions 3Úvoddokognitivníchfunkcí Cognitionandasociativecorticalareas Cerebralasymmetryandfunctionallateralisation Summary:phylogeneticalcharacteristicsofMan 21 22-23 24 1

  2. Nakoncitétokapitolybychommělibýtschopni: 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. Vysvětlitklidovýmembránovýpotenciál Vysvětlitprincipexcitability Popsatakčnípotenciálavysvětlitjehobinárnípovahu Vysvětlitvedenívzruchunervovýmvláknem Uvéstcílovétkáněafunkcemodulovanénervovouaktivitou Vysvětlitčasovýaprostorovýzpůsobkódovánínervovýchsignálů Popsatnervo-svalovouaktivaci Vysvětlitmolekulárnímechanismussvalovékontrakce Definovatfunkcekosterníhosvalstva Definovatmotorickoujednotkuamechanismykontrolysvalovésíly Definovatreflexauvéstpříklad(y) Popsatorganizacimotorickéhoprogramu Uvéstmetodyfunkčníhomapování Definovatasociačníoblastimozkovékůryajejichfunkčnívýznam Uvéstpříkladyfunkčnílateralizace Man:Volume~7.107mm3 S S P Respiration Nervous system STI MUL I S A DAPTAT ION BEHAVI OUR BloodImmunesystem internalmilieuHormonal circulationsystem Locomotorsystem Kidney P Skin Digestion RESPONSES P P offluxes(S,P)=0 stableparameters(T,P,V,composition,pHetc.) HomeostaticmechanismsinanmulticellularorganismarecalledREGULATIONS Regulationsarebasedoncooperationofallexchangingsystemsandtheyarecontrolledbynervous,endocrineandimmunesystems 2

  3. Membraneelectricalpotentialinarestingnervouscell Recall:[Na+]e=145mmol/l [Na+]i=15mmol [K+]e=4mmol/l [K+]e=136mmol/l [Cl-]e=120mmol/l [Cl-]i=8mmol/l Recall: E=+60mV Na Ei-e=-RTlnCi zFCe E=-93mV ion K E=-72mV Cl INa=GNa(Vm-ENa)andIK=GK(Vm-EK) K+ AtsteadystateINa=-IKthen: GNa(Vm-ENa)+GK(Vm-EK)=0thus: GK Na+ ATP ase ext K NachannelGNa channel GK SubstitutionofEionandVmvaluesgives: -75mV ~11-13 GNa GNaENa+GKEK Vm Alternatively:Vm~ K+ Na+ int G+G NaK GiventheNaandKdistribution,theRESTINGMEMBRANEPOTENTIALresultsfromthediffusionofNaandKdependingontheratioofNaandKconductances. Thustheionicdiffusiondissipatestheconcentrationgradientsthatmusthoweverremainstable (homeostasis):thisistheroleoftheNa,K,ATPase Thusionsareconstantlycirculatingacrossthemembranebutelectrochemicalgradientsremainstableattheexpenseofenergy:ATP 1 Membraneelectricalpotentialinanactivatednervouscell Whenthemembraneofanervousfibreissuddenlydepolarised: t=0ms L t=tt K+ Na+ ---++ +- - - - --- SPACE - + mV stimulus +60 ENa +30 actionpotential mV0 -30 TIME 5 10ms restingpotential -60 -90 EK 1)TheNavoltagesesnsitivechannelsopen(GNa>>>GK),NaentersthecellandVmapproachesforsomemillisecondsthevalueofENa~+60mV.Thechannelscloseagainandremainforacertaintimeinsensitivetoanewdepolarisation:refractoryperiod(RP). 2)ThentheKvoltagesensitivechannelsopenforsomemilliseconds(GK>>>GNa)andVmapproachesthevalueofEK~-90mV. 3)TheA,K,ATPasethenre-establishestheinitialionicconditions. Thusthemembranepotentialshowsabriefoscillationofabout100mVbetweentheENaandEK.Suchatransientdepolarisation,the ACTIONPOTENTIAL,isa"binarysignal"propagatingalongthemembraneandservingforarapidcommunicationbetweencells. TheconductionspeedofAPdependsonfiberdiameterandisolation(myelin):0.1-100ms-1.The1/RPdeterminesthemaximalsignallingfrequency:20-2000Hz 2 3

  4. Membraneelectricalpotentialinanactivatednervouscell Explanationatmicroscopicallevel: Inadditiontochannelsresponsiblefortherestingpotential,themembraneofnervousandmusclecellscontainsalsoNa,KandCavoltagesensitivechannels(transmembraneproteins)whichtemporarilyopenorcloseaccording totheactualvalueofVm. R=10G patchpipette Singlechannelcurrents(~pA) ip channelclosed Thebehaviourofmembranechannelscanbeexploredby «patchclamp»technique (Neher&Sackmann,Nobel 1991) V= R.ip Na+ nervecell channelopen patchofelectricallyisolatedmembrane ACTIONPOTENTIALresultsfromcurrentsthroughpopulations ofopenionicchannels voltagecommand Vc Presumedstructureofthe Navoltagesensitivechannel reference(extracellularmedium) 4 4 4 4 4 domainssensitivetovoltage domainsresponsible forconductionandselectivity P P P P P P 4 PP loopsdomainsresponsibleforinactivation 4 4 Thechannelmayadopt3conformationalstates: -closedandactivable -open -closedandtemporarilyinactivable(refractory) 3 Theuseofactionpotential Origin: Propagation: Axondeparturefromtheneuronalbody. Bylocalcircuitsor,inmyelinatedaxons,bysaltatoryconductionfromoneRanviernode(b)toanother. Inaxonterminals:presynapticbuttons(c). Termination: Transmission:Topostsynapticmembranesofanotherneurons(d),ortomusclecells(e),ortoepithelialcells(f). Atthesynapse,APleadstosecretionofneurotransmittersthatbindtoandmodifytheconductanceofpostsynapticmembranechannels. Effect: Excitationorinhibitionofpostsynapticneuron(d),initiationofmusclecontraction(g),modulationofsecretion/absorption(h)... b neuronalactivity: e.g.perception c d b a mechanicalactivity: posture&movement e c AP h g chemicalactivity: e.g.,secretion f c !Suchaneurondoesnotexist! Inreality,everypost-synapticactivity(ontheright) dependsonitsownspecificpre-synapticneuron! 4 4

  5. Twospinesoriginatingfromthesameneuronareshown.Theleftoneis“strong”(largeexcitatorypostsynapticpotential,EPSP),therightoneisTwospinesoriginatingfromthesameneuronareshown.Theleftoneis“strong”(largeexcitatorypostsynapticpotential,EPSP),therightoneis “weak”(smallEPSP). SYNAPTICMODULATIONS Phase1:IONOTROPIC Excitationontheleftactivatesthespine:depolarisation,amplifiedbydendriticvoltagedependentchannelspropagatesalongthedendriteandirradiatestowardstheneighbouringspines.Iftherightspineisactivatedatthesametimeandifsuchaco-activationhappensrepeatedly,itcandevelopalargerEPSP,i.e.itbecomesmoreefficient(longtermpotentiation MEMORYTRACE:possiblemechanismsspinesdependonelectrotonicpropagation(spineimpedance),dimensions(cytoskeleton)distributionofchannelsandmodulationby inhibitoryinputs. Phase2:METABOTROPIC Excitationontheleftalsotriggerscascadesofbiochemicalreactionsleadingtomodificationsofexistingpostsynapticreceptors. Phase3:Genomicmodifications Theinducedbiochemicalsignalsmayinducesynthesisandmembraneincorporationofnewreceptors. Phase4:RESTRUCTURATION Formationofnewandmorecomplexspines:increasedprobabilityofassociationbetweenthetwoexcitatorystimuli:MEMORYTRACE LTP).Thecommunicationamongthedendritic 5 Recall:muscle=linearmotormadeofproteins musclefibersconsistingofmyofibrils nervesfromspinalcord m.biceps decontracted contracted Z-line Z-line thinfilaments madeofproteinfilaments thickfilaments SARCOMERESrepeatingunits:striatedmuscle thinfilaments Z-line Z-line FORCEdeveloped duringcontraction: ~100N/cm2ofsection Noshorteningbutslidingoffilaments:L=workingstroke(cca9nm) L Actin PROTEIN:Actin Myosin Tropomyosin Ca++ + Troponin Myosin Actin head:bindingofactinATPaseworkingstroke inhibitsacto-myosin allowsinteraction FUNCTIONS:bindingsitesformyosin L 6 5

  6. Electro-mechanicalcoupling (excitation-contractioneventsinstriatedmuscle) acetylcholinefrompresynapticnerveterminals sarcolemma AP T-tubule nicotinicAChreceptor-channel sarcoplasmicreticulum + Na+ Ca++ ATP Ca++ contraction relaxation AM crossbridgecycling stroke:work+heat ~25% Force delay AP 10 20 40 50ms ATP creatinelacticacid ADP+P creatinephosphateglucose(glycogene) fattyacids/glucose+O2 energymetabolism RESERVESfor20s 60s 7 longeffortCO2 Rolesofthemuscles:POSTURE,MOVEMENT,HEAT,COMMUNICATION 8 6

  7. HOWISTHEMOTORACTORGANISED? CORTEX motor VISION ACCELERATIONsensory VOLUNTARY ACT associative HEARING sensoryselectionofintention programsmotivation motor plan analysis THAL AMUS ! ORIGINOFACTIVITY: CENTRALNERVOUSSYSTEM moduationofthecorticalactivity tractuscortico spinal posturevsmovementadjustment plan filtering initiation BRAINSTEM CEREBELLUM CENTRALGREYNUCLEI modulationof andmotorunits spinalcircuits MOELLE activationofMU MOTORUNIT contraction: forceshortening motoneuron RECEPTORS REFLEX peripheralstimulus motoract 9 RECRUITEMENT: ↑Nbofmotorunits motoneuronalpool Howthebrain controlsthemuscleforce? 10 7

  8. SUMMATION: ↑frequencyofAP Unitfiringrate(Hz) Howthebrain controlsthemuscleforce? voluntaryforce(g) 11 Innervationandreceptorsoftheskeletalmuscle musclespindle: ventralroot Spinalcord intrafusalmotorfibres&Aterminals dorsalroot annulo-spiralterminals extrafusalmotorfibres tendonorgan Musclespindle:inparallelwiththemusclefibersofmotorunits formedby-sensorypart(IandIIterminalssensibletoelongation) -motorpart(striatedmusclefibersinnervatedbymotorneurons) Tendonorgan(Golgi)inserieswiththemusclefibersofmotorunits formedbynervousterminalsintermingledwiththetendonconnectivefibers 12 8

  9. 2passiveelongation 1initiallength 3 Intrafusalcontraction 4extrafusalcontraction 5extra-&intrafusalcontraction (Astimulation)(Astimulation) Musclespindle: mechano-receptorcontrolledbythebrain -recordsthemusclelength -itssensitivityandgainiscontrolledbytheCNS Iafibreactivity musclelength 13 Proprioceptivereflexes MYOTATIC(STRETCH/JERK)REFLEX INVERSEMYOTATICREFLEX Stimulus:muscleelongation (gravity!)Response:contractionofthe elongatedmuscle Importance:maintainspostural (antigravitationaltone) Stimulus: tendonelongation(musclecontraction!)relaxationofthecontractedmuscle Response: Importance:limitstheforce,defendsagainstthemusclelesion 14 9

  10. Heteroceptivereflexes NOCICEPTIVEREFLEX Stimulus:pain(lesion)Response:contractionofmuscles leadingtowithdrawalfromthestimulus Importance:protectionagainst lesions 15 POSTURALSENSE:kinesthesia+vision+equilibrium SKIN, ARTICULATIONS posteriorfascicles spinocerebellartract CNS tectospinalepathways perturbations definitionofthebehaviouralvertical/horizontal,awakeningreaction,affectivity,interpretation vestibulo-ocularpath vestibulospinalpathways fasc.longitudinalmedial vestibulo-ocularpathways PositionoftheHEADwithrepecttotheBODY MUSCLES TONIC&PHASIC* REFLEXES EYES retinotectalpathway LABYRINTH vestibularnerve *MODULATIONOFTHEMUSCLETONE(verticalaxispassingthroughthegravitycenterwithinthesustentationpolygon) **COMPENSATORYMOVEMENTS (nystagmus,swaying,jump) 16 10

  11. VOLUNTARY MOTORCOMMANDCortico-spinal(pyramidal)tract motorcortex somato-sensorycortex 17 muscles VOLUNTARYMOTORCOMMAND Organisationofthemotorcortex PRECISECARTOGRAPHYOFTHEMUSCLES: somatotopicalprojection:pointbypoint “pianokeys→correspondingcords” MOTORHOMUNCULUS INNERVATIONDENSITY: moredelicateisthemovementhigheristhenumberofmotorneuronsinnervatingthemuscle Specificallyhumanfunctions: manualexplorationandmanipulationverbalcommunication tothemuscles: cortico-spinaltract 18 11

  12. Increaseofthebloodperfusion Butwhereisthepianist? Functionalcartography Principle: activeregionsaremoreirrigated Realisation: measurementof thebloodperfusion MRIf whichcerebralstructuresareinvolvedinthediscriminationofformesbytherighthand? successivelyexplore2objects,thendecideiftheyareidentical Example: Task: -understandingandrecallofinstructions -tactileexploration -extractionfromthesensoryinformationofthecharacteristicalfeaturesoftheobject -mentalreconstructionoftheobject -memorisationoftheobject -comparaisonwiththementalimageoftheotherobject -decision -motorcommand:response ThetaskisdistributedoverMULTIPLECORTICALANDSUBCORTICALSTRUCTURES. AllthesestructuresareindicatedontheslideNb8. 19 SUMMARY:Organisationofamotorprogramme PREPARATION EXECUTION MOTIVATION&INTENTION Iwill(must)writemysignature Association&Limbiccortex CentralGreyNuclei CONTEXT Where?Size?Speed?Paper?Blackboard?Standing?Sitting? ACTION Motorcortex Association&(Pre)motorcx Cerebellum STATE Eyesopen?Equilibrium? Position:shoulder->wrist Forcevsresistance… Association&Sens.-mot.cx APRAXIA: noparalysisbutimpossibilitytoexecutecomplexmovements Motorlearning: aperceptive(observation) cognitive Motormemory:implicit(non-declarative),«procedural» CEREBELLUM CENTRALGREYNUCLEI ASSOCIATIVECORTEX 20 12

  13. Corticalassociationareas:indispensableforCOGNITIVEBEHAVIOUR Cognition=thehighestmentalfunctions: abstraction (self-)consciousness language purposefulactions MOTORAREAS SOMATO-SENSORYAREAS spatialcoordinatesofthebody &environment planificationofcomplexmovementelaborationofthoughts spokenlanguage understan-dingoflanguage memory reading HEARING instinctive behaviouremotions motivation visualrecognitionofobjects VISION Corticalassociationareas(CAA) ThefunctionsoftheCAAarededucedfrom: -analysisofregionalbloodflow -PET(positronemissiontomography) -functionalmagneticresonanceimaging 1)Physiologicaldata: -havenodirectconnections withthesensoryormotorperiphery -arelocalisedin:frontal,parieto-occipito-temporalandlimbicbrainregions -areextensivelydevelopedinhumans 2)Clinicalobservations(neuropsychologydeficits): -agnosias(difficultiestorecognizeandunderstand) -apraxias(difficultiestoexecutecomplexmovements) -aphasias(difficultiestounderstandand/orproducelanguage) 21 -alterationsofpersonalityandsocialbehavior StudiesofLANGUAGE InthemajorityofsubjectsthelanguageisassociatedwiththeLEFThemisphere: CEREBRALDOMINANCE WordsseenpassivelyWordsheard WordsrepeatedSpontaneousspeech CorticalassociationareasinvolvedinLANGUAGE(functionalbrainimaging) Wernicke Wordsseenpassively Wordsheard Broca !Subcorticalstructuresareactivatedaswell:e.g.,basalganglia,thalamus! Spontaneousspeech Wordsrepeated LesionsofareaofWernicke,areaofBroca,andtheirreciprocalconnectionsresultin APHASIAs Alterationsoforalexpression,comprehensionandrepetition 22 13

  14. section Lateralisationofcerebralfunctions Studiesinhumans“Splitbrain” Thehumansshowmany FUNCTIONALasymmetries: -manualpreference -ocularpreference -language -othercomplexfunctions Selectiveinterrogationofhemispheresrevealedthatfunctionsoftheleft andrighthemispheresarenotsymmetricalalsoinother, non-verbaldomains Thecerebrallateralisation: -isnotpredictablebythemanualpreference -isnotpredictablebyanygeneticmodel -developsduringchildhood -ispronouncedmoreinmalesthaninfemales LEFTHEMISPHERE RIGHTHEMISPHERE VISUALSYSTEM Ietters,words compleximages(faces) AUDITORYSYSTEM soundslinkedtolanguage music,soundsnon-linkedtolanguage SOMATOSENSORYS. tactilerecognition(Braille) MOTORSYSTEM complexvoluntarymovements MEMORY verbal visual LANGUAGE speaking,reading,writing SPACE orientation,complexgeometry “COGNITIVESTYLE” rational,analytic,sequential,detail intuitive,synthetic,simultaneous, holistic 23 SUMMARY(organisationofcognitivefunctions): ThecorrectfunctioningofCAAismandatoryfor -integrationofpluri-sensoryinformation -planningandinitiation(alsoinhibition)ofbehavior -formationandstorageofinternalconcepts -abstraction(thoughts,language,consciousness) -emotionality Openquestions: Doeseachhemispherehaveitsownconsciousness? Ifso,whatmechanismsunifythebehavior? Whatistheadvantageoffunctionalasymmetry? Abitofphilosophy:whatarethehumancharacteristics? Locomotiononhindlegs:forelimbsfreeforotherfunctions Prehensilehand:toolsanddevelopmentoftechnology Enlargementofbrainrelativetobodysize(inhibitoryneurons!) Developmentofspeechandlanguage Consciousessofselfandofenvironment Developmentofsocialinteractionsandculture NO! tomy«id» Divisionoflabourinsociety Ethics,artisticandspiritualexpresion 24 14

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