l007 motor system

8/12/2019 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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l007 motor system

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