Download 10 Control of Movement

Physiology
Unit2
CONTROLOFMOVEMENT
InPhysiologyToday
MotorProgram
• Patternofneuralactivityrequiredtoproperlyperformthedesired
movement
• Highestlevel
– Motorcortex
– Decidewhatmovementwilloccur
• Middlelevel
– Cerebellum,basalganglia,thalamus,brainstem,spinalcord,
– Posturesandmovementsneededtocarryouttheaction
– Receivessensoryinputfromlocallevel
• Locallevel
– Brainstem,Spinalcord
– Afferentneurons,Motorneurons,Interneurons
– Monitorsmusclelengthandtensionconstantlyadjustingmuscle
contraction
ControlofBodyMovement
Motor
Control
Hierarchy
LocalControlofMotorNeurons
• Localcontrollevelsarerelaypointsfor
instructionscomingfromhigherlevelsinthe
motorprogram
• Adjustingmotorunitactivitytolocalconditions
(obstaclestomovement,pain)
• Localcontrolsystemsusesensoryinformation
fromsensoryreceptors
–
–
–
–
Muscles
Tendons
Joints
Overlyingskin
SomaticNervousSystem
Interneurons
•
•
•
Mostofthesynapticinputfrom
descendingpathwaystomotor
neuronsarefrominterneurons
90%ofspinalcordneurons
Integrateinputs
– Highercenters
– Peripheralreceptors
– Otherinterneurons
•
Determinewhichmusclesare
activatedandwhen
– Coordinatesrepetitive,rhythmic
activities
• Walking,running
•
Canturnmovementsonoroff
– Grabbingahotplate
ReflexArc
• Thebasicanatomical/functionalunitofthe
nervoussystem
• Components:
1.
2.
3.
4.
5.
Sensoryreceptor
1st ordersensoryneuron
Integratingcenter(brain/spinalcord)
Motorneuron
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
• Afferentfibersbringinformationfromsensory
receptorsfrom
– Skeletalmuscles(primemovers)
– Nearbymuscles(synergists,antagonists,fixators)
– Tendons,jointsandskinaffectedbythemovement
• Sensoryreceptorsforlocalskeletalmuscle
controlmonitor
– Lengthandtension
– Jointmovement
AscendingTracts
LengthMonitoringSystem
• Musclespindlestretch
receptors
– Stretchreceptorsembedded
inmuscle
• Monitormusclelength
• Themoreorthefasterthe
muscleisstretched the
greatertherateofreceptor
firing
• Contraction ofthe
extrafusalfibersshortens
themuscleandslowsdown
therateoffiring
Alpha-GammaCo-Activation
• Preventslossofsensory
informationwhenthe
muscleiscontracting
• Alphamotorneurons
– Extrafusal fibers
• Gammamotorneurons
– Gammamotorneurons
stimulatethetwoendsof
theintrafusal fibersto
contract
– Maintainstensioninthe
spindleapparatus
TensionMonitoringSystems
• Tensiondependson
– Musclelength
– Loadonmuscle
– Degreeofmusclefatigue
• Sensoryinformationon
tension
– Vision
– Somatosensoryinput
– Golgitendonorgans
• Inhibitorysynapses
preventexcessive
contractionorpassive
stretching
MonosynapticReflex
– Reflexresponsethat
involvesONLY one
synapse
– Sensoryneuronfromthe
extensormuscle
synapseswiththemotor
neuronforthatextensor
muscle
– Onlyfoundinthestretch
reflex
PolysynapticReflex
• Reflexresponsethat
involvesMORETHANone
synapse
– Interneurons
• Ipsilateral’sflexormuscle’s
motorneuronstimulated
– Withdrawalreflex
• Oppsositelimb
(contralateral)extendedto
supportthebodiesweight
– Crossedextensorreflex
ControlbytheCerebralCortex
• Planningandcontrolling
ongoingmovement
• Motorcortex,premotor
area
– Givesrisetomostnerve
fiberstodescending
pathwaysformotorcontrol
• Corticalneuronsforma
neuralnetwork
– Manyneuronsparticipatein
eachsinglemovement
– Coordinationofmanypartsto
produceasmooth,
purposefulmovement
SubcorticalandBrainstemNuclei
• Planningandmonitoringmovement
• Establishtheprogramthatdeterminesthe
specificsequenceofmovementsneededto
accomplishadesiredaction
• Basalganglia
– Subcorticalnuclei
– Linkcircuits
• Somefacilitatemovements
• Somesuppressmovements
Cerebellum
1. Influencesbalanceandposture
– Inputtobrainstemnuclei
2. Providestimingsignalstothecortexandspinal
cord
– Forpreciseexecutionofdifferentphasesofthemotor
program
– Agonist/antagonisttiming
3. Coordinatesmovementinvolvingmultiplejoints
4. Storesmemoriesofmovements
- Easiertoaccomplishthenexttime
TypesofDescendingPathways
• PyramidalTract(corticospinalpathway)
– Planningtracts
– Frommotorcortex
– Excitatory
• ExtrapyramidalTract(brainstempathway)
– Coordinatingtracts
• Excitatory/Inhibitory
– Frombrainstem
– Coordinatethe“plan” fromthemotorcortex
– Maintainpostureduringmovement
DescendingPathways
CorticospinalPathway
• Pyramidaltract
• Nervesfrommotorcortex
terminateinthespinal
cord
• Decussation ofthe
pyramidsinmedulla
• Convergence/divergence
• Controlmusculature
involvedinfineisolated
movements
– Hands,fingers
DescendingPathways
BrainstemPathway
• Extrapyramidaltract
• Nervesinthebrainstem
terminateinthespinal
cord
• Mostlyipsilateral
• Controllargemuscle
groups
– Posture
– Locomotion
– Head,bodymovements
turningtowardsa
stimulus
MuscleTone
• MuscleTone
– Resistancetostretch
– Tension
– Elasticpropertiesofmuscle,tendons
• Slightlycontractedstateofmusclesevenatrest
• Maintainedbystretchreflexes
• Function
– Helpsstabilizejoints
– Improvesposture
– Createsoptimallengthformusclecontraction
• Requiresconstantsensoryfeedbacktocontrolmuscle
activity