l007 motor system
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MOTOR SYSTEM
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INTRODUCTION
Every movement needs motor systeme.g. : reading, writing, talking, walking,
watching tv, playing instruments, etcOrchestrated by coordinated action ofmulti organs or regions of nervous systemHow if the system doesnt work? e.g. : hemiparesis/plegi, tetraparesis/plegi,
paraparesis/plegi
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Decision
Motor planning areas
Control circuits
Descending motor pathways
Spinal interneurons
Lower motor neurons
Skeletal muscles
Schematic figure ofNeural structures inmotor system
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Lower motor neuron innervate skeletal muscle
Spinal motorneurons act in spinal region
Descending pathway deliver motor information from brain to LMN postural/gross & fine movement pathways
Control circuits Basal ganglia & cerebellum
Motor planning area frontal cortex
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Motor planning
Control circuit
D e s c e n
d i n g p a t
h w a y
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LOWER MOTOR NEURON
2 types : & motoneuronCell body ventral/post horn of spinal cordSpinal cord ventral root (radix ventralis) peripheral nerve skeletal muscleCharacteristics of motoneurons :
Axontype
Size & myelination Innervates
Large myelinated Extrafusal musclefibers
Medium myelinated Inrafusal musclefibers
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Motor Units
An motoneuron & muscle fibers it innervatesVaried in number of muscle fibers innervated
Gastrocnemius : >1000 fibers/motoneuron
Extraocular muscle : 10 fibers/motoneuron
motoneuron activation acetylcholine releasedat NMJ muscle contraction
According to speed of muscle contraction inresponse to single electrical shock, classified into :- Slow twitch : postural muscle, activated first- Fast twitch : powerful movement (gastrocnemius)
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SPINAL REGION
2 types of movement Automatic / Voluntary / Anticipatory
Complex
Supra spinal circuit neededSpinal region coordinationReflexive
Simple
Not need supra spinal circuitSpinal reflex
Proprioceptive reflexCutaneous Reflex
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Proprioceptive ReflexMuscle stretch reflex
Mono/multi synaptic reflexReciprocal inhibition
Inhibit antagonist muscleGolgi tendon organ reflex
Autogenic inhibition
Cutaneous ReflexWithdrawal reflex
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Muscle stretch reflex
Golgi tendon
organ reflex
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Spinal Region Coordination
The role of spinal circuit beyond reflexControl movement as part of motor system
Part of descending tractLesion monoparesis, hemiparesis,
paraparesis, quadri/tetraparesis
Central pattern generatorProven in experimental animalsStill hypothesis in human
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DESCENDING MOTOR PATHWAY(UPPER MOTOR NEURON)
Projects from supraspinal center to lowermotor neuron in brainstem & spinal cord
Classified according to synaps location :Medial activation system
for postural & gross movementLateral activation system
for fine movementNonspecific activating pathway
local reflex arc
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Medial Activation System4 tracts from brain stem
Tectospinal tract Activate cervical spinal cord for head movement
Medial reticulospinal tract
Head movement & limb extensorMedial vestibulospinal tract Control neck & upper back (cervical & thoracal)
Lateral vestibulospinal tract Maintain equilibrium in upright position
1 tract from cerebral cortexMedial corticospinal tract
Control neck, shoulder & trunk muscles
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Nonspecific Activating Pathways
Enhanced the activity of onterneurons andmotorneurons in spinal cord
Consist of :1. Ceruleospinal tract
From locus ceruleus
2. Raphespinal tract From raphe nuclei
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CONTROL CIRCUITS
Basal ganglia and cerebellumInfluence motor area in cortex via thalamus
Project to brainstem to control descendingpathway
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Basal GangliaNucleus (gray matter) in cerebrum & midbrain :
Nucleus caudatusPutamen
Nucleus lentiformis
Globus palidusNucleus subthalamicusSubstantia Nigra
Neurotransmitters :GABA, Substance P & DopaminFunctions :Iniciation, facilitation and sequencing of movements,Motor synergy, regulating muscle tone and muscle force
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Basal Ganglia
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Cerebellum
Basic functions :Coordination of movementPostural controlMuscle tone
Gross anatomy :3 lobes : anterior, posterior, flocculonodularVermis
Functional anatomy :Vestibulocerebellum (flocculonodular) : equilibriumSpinocerebellum (vermis) : movementCerebrocerebellum : planning and accuracy
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Cerebellum
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Vestibulocerebellum
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Spinocerebellum
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Cerebrocerebellum
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THANK YOU