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