bn20 cortical motor control ppt 2384
TRANSCRIPT
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Cortical Control
of Movement
Lecture 20
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Hierarchical Control of Movement
Association cortices & Basal Ganglia
strategy : goals & planning
based on integrationofsensory info Motor cortex & cerebellum
tactics: activationofmotor programs
Spinal cord execution: activationofalpha motor
neurons ~
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Sensorimotor Cortical System
Integrationofsensory information
and directed movements
Anatomy Descendingspinal tracts
Lateral pathway
Pyramidal MotorSystem Ventromedial pathway
Extrapyramidal pathway ~
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Cortical Anatomy
S1 - postcentral gyrus
PPC - Posterior Parietal Cortex
M1 - Precentral Gyrus Frontal Lobe
somatotopic organization
M2 - SecondaryMotor Cortex SMA - SupplementaryMotorArea
PM - Premotor Cortex ~
M1
SMA
S1
PM
PPC
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M1 S1
PM
SMA
PPC
P
r
e
fr
o
n
ta
l
Sensorimotor Pathways
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Primary Motor Cortex
Somatotopic organization
neurons have preferred directionof
movement
Motor homunculus ~
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M1: Coding Movement
Movement for limbs
Neuron most active
Preferred direction but active at 45r from preferred
How is direction determined?
PopulationsofM1neurons Net activityofneurons with
different preferred directions
vectors ~
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M1: Coding Movement
Implications
1.Most M1 active for every
movement
2. Activityofeach neuron1 vote
3. direction determined by
averaging all votes ~
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Motor Association Cortex
Motor area other thanM1
Premotor & Supplemental MotorAreas
Active during preparationfor movement
Planningofmovements
Stimulation - complex movements
motor programs
Active during preparationfor movement
Planningofmovements
e.g.finger movements ~
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Motor Association Cortex
Active before movement
Supplemental MotorArea
Bilateral lesions unable to move or
speak voluntarily
Some reflexive movement retained
Premotor
Unilateral lesion impaired stability,gait, hand coordination
Fine motor control OK ~
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M1 S1
PMA
SMA
Spinal cord
PPC
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Planning Movements
Targeting vs triggerstimulus
recording activityofneurons
active when movement planned forspecific direction
Different populationsofneurons active
during planning (targeting) & execution (triggerstimulus) ~
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Simple fingerflexion
onlyM1 activation
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Sequence ofcomplex finger movements
M1 + SMA activation ~
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Mental rehearsal offinger movements
onlySMA activation ~
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The Descending Spinal
Tracts
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Brain to Spinal Cord
Upper motorneurons
communication with lower (E) motor
neurons
Lateral pathway
direct cortical control
Ventromedial pathway brainstem control ~
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The Lateral Pathway
Voluntary movement
distal limbs
Corticospinal (Pyramidal) tract Primary pathway (> 1 millionneurons)
Contralateral control movement
Cortico-rubrospinal tract Via red nucleus
But some recovery ifdamage to
corticospinal ~
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Dorsal
Ventral
Spinal Cord: Lateral Pathway
Corticospinal
tract
Cortico-
rubrospinal
tract
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The Ventromedial Pathway
Neuronsoriginate inbrainstem
Vestibulospinal & tectospinal tracts
head & posture posture orienting responses
Pontine & medullary reticulospinal tracts
originate in reticularformation trunk & antigravity leg muscles
tracts are antagonistic ~
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Major Descending Spinal Tracts
Motor Cortex
Spinal cord
Red
Nucleus
Reticular
Nuclei
Superior Colliculus
vestibularnuclei
VentromedialLateral