chapter v movement disorders part i: anatomy and physiology of motor system
TRANSCRIPT
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CHAPTER VMovement disorders
Part I: Anatomy and physiology of motor system
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Motor systems
• Motor systems are complex and include sophisticated control systems the purpose of which is to serve locomotion, posture and work.
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Several feedback systems monitor muscle activity
The length of muscles and the strength of contractions are monitored by:
– Input from proprioceptive receptors in muscles, joints and tendons
– Local feedback from motor nerves (Renshaw inhibition)
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Posture
Monitored by
• proprioceptors,
• vestibular system
• vision
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Causes of movement disorders
• More or less anatomically specific neural degeneration
• Injuries (trauma, strokes, surgery, etc)
• Chemicals (alcohol, drugs)
• Inflammations and infections (viral)
• Tumors
• Genetic
• Neural plasticity
• Genetic
• Idiopathic
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Motor disorders
• Lack of function
• Inadequate function
• Hyperactivity
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Disorders of motor systems
• Hypokinesia
• Hyperkinesia
– Spasticity
• Ataxia
• Gait and balance disturbances
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Two different descending motor pathways:
• Lateral system– Fine movements
• Medial system– Posture etc.
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Cortex(MI)
Internal capsule
BrainstemNucleus ruber
Midline
Propriospinalinterneuron
Pyramids
Spinal cord
a motoneuron
Distal limb muscles
Lateral system
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Medial system
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Motor pathways
The motoneurons (alpha motoneurons) are the final common pathways
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The alpha-motoneurons (common final pathway) receive many inputsSome are facilitating and some are inhibitory
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Motor pathways
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Somatotopic organization of the motor cortex
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Colony
Colony
Two motoneurons receiving input from cortical cells
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Motor areasSensory areas
Terminations of the corticospinal tract projections of sensory pathways
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Corticospinaltracts
Propriospinalinterneuron
Supraspinalinput
Ia interneuronSegmental
input
Renshaw cellMuscle
a motoneuron
a motoneuron
Midline
Renshaw inhibition
Fibers of the corticospinal tract terminate onmotoneurons or interneurons
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Extensive processing of motor command occurs in the spinal
cord (and brainstem)
• Spinal reflexes play an important role in all motor functions
• Some functions such as walking is programmed in the spinal cord
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From supraspinalsources
InterneuronPresynaptic(Axo-axonic)
synapse
Muscle
Muscle spindelafferent
la fibers
DRG
a motoneuron
Monosynaptic stretch reflex
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Stimulus
Stimulus
Stimulus strength (V)
Antidromicmotor
Motor
Orthodromicmotor (reflex)
EMG
A
B
C
10ms
M-wave H-reflex
400
2
4
6
8
80 120
M
H
Hoffman reflex
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Reflexes are modulated from supraspinal sources
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Supraspinalinput
la interneuron
Inhibition ona motoneuron
Agonistmuscle
Antagonistmuscle
Musclespindel
Stretch reflex arc
DRG
a motoneuron
Reciprocal spinal reflex
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From semicircular canals
From uticulus
Lateralvestibularnucleus
Medialvestibularnucleus
Medialvestibular
spinal tractLateral
vestibularspinal tract
Spinal cord
a motoneurons
motoneurons
Descending vestibularpathways
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Medial systemPosture and automatic functions
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Reticulospinal tract
la interneuron
Muscle
Tendon
Golgi tendonafferent
DRG
a Motoneuron(inhibitory input)
Tendon reflex
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Reticulospinal pathway
la interneuron
Extensormuscle
Flexsormuscle
Flexor reflexafferents
a Motoneurona Motoneuron
Inhibitoryinterneuron
Excitatoryinterneuron
Flexor reflex
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Interneuron
Input A
B
A
a motoneuron
Input B
Intracellularpotential in
a motoneuron
Input A
B
A
a motoneuron
Input B
Intracellularpotential in
a motoneuron
Convergence of excitatory inputs
Convergence of inhibitory and excitatory inputs
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Muscle
lb inhibitory
Forelimbafferents
la excitatory
Decending motor tracts
a motoneuron
Input to propriospinal neurons of the forelimb of the cat
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From Rosler Fig 2B
Magnetic stimulation of motor cortex in an awake individual
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MuscleMuscle
la afferents
Fromantagonist
musclespindle
From agonist muscle spindle
Renshaw
FRA
Corticospinal tractand interneurons
Contralat. Vest.Spinal, FRA etc.
Ipsi. vestibular tractPropriospinal input
Antagonista motoneuron
Agonista motoneuron
Input to an Ia inhibitory interneuron
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Muscle
laNorepinephrineserotonin tract
Dorsal reticularspinal tract
lb
Decending motor tracts
Joint receptors
Skin receptors
a motoneuron
Input to an Ib (inhibitory) interneuron
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BASAL GANGLIA
Extrapyramidal system
Pyramidal system
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Cortex
To spinal cord
Thalamus
Basalganglia
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Cerebellum
Corticospinaltract
Brain stemmotor pathways
Interneurons
Motor cortex
Basalganglia
Thalamus
a motor neuron
muscle
Two descending motor tracts
The alpha-motoneuron is the final common pathway
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Fig 5.27B
Anatomical localizationmotor pathways
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Motor cortex
Caudatenucleus
Putamen
Claustrum
Globuspallidus Subthalamic
nucleus
Substantianigra
Thalamus
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Basal ganglia
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Parkinson’s disease
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Huntington’s disease
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SMA/PMC/CM
GPi/SNr
Putamen
Indirect Direct
GPe
STN
BrainstemSpinal Cord
VLoVApc/mc
CM
Direct and indirect pathways
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SMA MI
Putamen
Globus pallidus
STNThalamusVlo-CM
Basal ganglia connect to supplementary motor areas and primary motor cortex
SMA: Supplementary motor area
STN: Subthalamic nucleus
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Cortex
Thalamus
Dentatenucleus
Pontinenuclei
Cerebellarcortex
Involvement of the cerebellum
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Cerebral cortex(MI and SI)
Thalamus
Cerebellarnucleus
Pontinenuclei
Rednucleus
Cerebellarcortex
Fromspinal cord
Rubrospinaltract
Involvement of the cerebellum and pontine nuclei
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Overview of motor pathways
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ANATOMICAL LOCATIONS OF THE BASAL GANGLIA
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Middle cerebral artery
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BASAL GANGLIA
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ANATOMICAL LOCATION OF THE CAUDATE NUCLEUS
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Somatotopic organization of the motor cortex
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Cortical motor areas
The central sulcus divides motor and sensory areas
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Overview of motor pathways
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Cerebellum
Corticospinaltract
Brain stemmotor pathways
Interneurons
Motor cortex
Basalganglia
Thalamus
a motor neuron
muscle
Two descending motor tracts
The alpha-motoneuron is the final common pathway
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Motor cortex
Spinal cord
Basalganglia
BrainstemCerebellum
Thalamus
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80
90
100
110
120
2 3 4 5 6 7 8 9 10Conditioning-test interval (ms)
Effect from spasticity
Soleus H-reflex: Effect on Ib inhibition on reflex response
Hemiplegic side
Normal side
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Inhibitory supraspinal input to motoneuron pool
Segmental input
Muscle
la(from muscle spindles)
lb(from Golgi tendon organs)
Supraspinal input
a motoneuron
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Spinal cord
T11-L4
S3-S4
Viceralafferents
Uterus
Efferent
Nociceptors
Viceralafferents
DRGDRG
Viceralafferents
Painfibers
Viceralreceptors
Bladder
Visceral afferent innervation in the lower body and motor (efferent) innervation.