10 control of movement - mtsac.edufaculty.mtsac.edu/mpresch/36_lecture_files_unit_2/10 control...
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CONTROLOFMOVEMENT
PhysiologyUnit2
InPhysiologyToday
MotorProgram• Patternofneuralactivityrequiredtoproperlyperformthedesired
movement• Highestlevel
– Motorcortex– Decidewhatmovementwilloccur
• Middlelevel– Cerebellum,basalganglia,thalamus,brainstem,spinalcord,– Posturesandmovementsneededtocarryouttheaction– Receivessensoryinputfromlocallevel
• Locallevel– Brainstem,Spinalcord– Afferentneurons,Motorneurons,Interneurons– Monitorsmusclelengthandtensionconstantlyadjustingmuscle
contraction
ControlofBodyMovement
MotorControl
Hierarchy
LocalControlofMotorNeurons• Localcontrollevelsarerelaypointsforinstructionscomingfromhigherlevelsinthemotorprogram
• Adjustingmotorunitactivitytolocalconditions(obstaclestomovement,pain)
• Localcontrolsystemsusesensoryinformationfromsensoryreceptors– Muscles– Tendons– Joints– Overlyingskin
SomaticNervousSystem
Interneurons• Mostofthesynapticinputfrom
descendingpathwaystomotorneuronsarefrominterneurons
• 90%ofspinalcordneurons• Integrateinputs
– Highercenters– Peripheralreceptors– Otherinterneurons
• Determinewhichmusclesareactivatedandwhen– Coordinatesrepetitive,rhythmic
activities• Walking,running
• Canturnmovementsonoroff– Grabbingahotplate
ReflexArc
• Thebasicanatomical/functionalunitofthenervoussystem
• Components:1. Sensoryreceptor2. 1st ordersensoryneuron3. Integratingcenter(brain/spinalcord)4. Motorneuron5. Effectororgan(skeletalmuscle,cardiacmuscle,smooth
muscle,glands)
ReflexArcComponents
1. Sensoryreceptor– Constantlysamplesitsenvironment
• Phasicreceptors• Tonicreceptors
2. 1st ordersensoryneuron– Afferent,peripheral;leadingtotheCNS
3. Integrating/coordinatingcenter– Centralnervoussystem
• Processesallincomingsensoryinformation• Integratessensoryinformation• Coordinatesmotorcommands
ReflexArcComponents
4. Motorneuron– Efferent,peripheral;leadingfromtheCNS
• Somaticmotorneuron• Autonomicmotorneuron
• Sympatheticdivision• Parasympatheticdivision
5. Effectororgan– Amuscleoraglandthatresponds– Skeletalmuscle(somatic)
– Smoothmuscle,cardiacmuscle,glands(autonomic)
TheSpinalCord:ReflexArc• Controlsreflexactivity
LocalAfferentInput
• Afferentfibersbringinformationfromsensoryreceptorsfrom– Skeletalmuscles(primemovers)
– Nearbymuscles(synergists,antagonists,fixators)– Tendons,jointsandskinaffectedbythemovement
• Sensoryreceptorsforlocalskeletalmusclecontrolmonitor– Lengthandtension– Jointmovement
AscendingTracts
LengthMonitoringSystem• Musclespindlestretch
receptors– Stretchreceptorsembedded
inmuscle
• Monitormusclelength• Themoreorthefasterthe
muscleisstretched thegreatertherateofreceptorfiring
• Contraction oftheextrafusalfibersshortensthemuscleandslowsdowntherateoffiring
Alpha-GammaCo-Activation• Preventslossofsensory
informationwhenthemuscleiscontracting
• Alphamotorneurons– Extrafusal fibers
• Gammamotorneurons– Gammamotorneurons
stimulatethetwoendsoftheintrafusal fiberstocontract
– Maintainstensioninthespindleapparatus
TensionMonitoringSystems• Tensiondependson– Musclelength– Loadonmuscle– Degreeofmusclefatigue
• Sensoryinformationontension– Vision– Somatosensoryinput– Golgitendonorgans
• Inhibitorysynapsespreventexcessivecontractionorpassivestretching
MonosynapticReflex– ReflexresponsethatinvolvesONLY onesynapse
– Sensoryneuronfromtheextensormusclesynapseswiththemotorneuronforthatextensormuscle
– Onlyfoundinthestretchreflex
PolysynapticReflex• Reflexresponsethat
involvesMORETHANonesynapse– Interneurons
• Ipsilateral’sflexormuscle’smotorneuronstimulated– Withdrawalreflex
• Oppsositelimb(contralateral)extendedtosupportthebodiesweight– Crossedextensorreflex
ControlbytheCerebralCortex• Planningandcontrolling
ongoingmovement• Motorcortex,premotor
area– Givesrisetomostnerve
fiberstodescendingpathwaysformotorcontrol
• Corticalneuronsformaneuralnetwork– Manyneuronsparticipatein
eachsinglemovement– Coordinationofmanypartsto
produceasmooth,purposefulmovement
SubcorticalandBrainstemNuclei
• Planningandmonitoringmovement• Establishtheprogramthatdeterminesthespecificsequenceofmovementsneededtoaccomplishadesiredaction
• Basalganglia– Subcorticalnuclei– Linkcircuits• Somefacilitatemovements• Somesuppressmovements
Cerebellum
1. Influencesbalanceandposture– Inputtobrainstemnuclei
2. Providestimingsignalstothecortexandspinalcord– Forpreciseexecutionofdifferentphasesofthemotorprogram
– Agonist/antagonisttiming3. Coordinatesmovementinvolvingmultiplejoints4. Storesmemoriesofmovements- Easiertoaccomplishthenexttime
TypesofDescendingPathways
• PyramidalTract(corticospinalpathway)– Planningtracts– Frommotorcortex– Excitatory
• ExtrapyramidalTract(brainstempathway)
– Coordinatingtracts• Excitatory/Inhibitory
– Frombrainstem– Coordinatethe“plan” fromthemotorcortex–Maintainpostureduringmovement
DescendingPathwaysCorticospinalPathway
• Pyramidaltract• Nervesfrommotorcortex
terminateinthespinalcord
• Decussation ofthepyramidsinmedulla
• Convergence/divergence• Controlmusculature
involvedinfineisolatedmovements– Hands,fingers
DescendingPathwaysBrainstemPathway
• Extrapyramidaltract• Nervesinthebrainstemterminateinthespinalcord
• Mostlyipsilateral• Controllargemusclegroups– Posture– Locomotion– Head,bodymovementsturningtowardsastimulus
MuscleTone• MuscleTone– Resistancetostretch– Tension– Elasticpropertiesofmuscle,tendons
• Slightlycontractedstateofmusclesevenatrest• Maintainedbystretchreflexes• Function– Helpsstabilizejoints– Improvesposture– Createsoptimallengthformusclecontraction
• Requiresconstantsensoryfeedbacktocontrolmuscleactivity