Transcript BN20 cortical motor control

Cortical Control
of Movement
Lecture 20
Hierarchical Control of Movement
Association cortices & Basal Ganglia
 strategy : goals & planning
 based on integration of sensory info
 Motor cortex & cerebellum
 tactics: activation of motor programs
 Spinal cord
 execution: activation of alpha motor
neurons ~
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Sensorimotor Cortical System
Integration of sensory information
 and directed movements
 Anatomy
 Descending spinal tracts
 Lateral pathway
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Pyramidal Motor System
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Ventromedial pathway
Extrapyramidal pathway ~
SMA
Cortical Anatomy
M1
S1
PM
S1 - postcentral gyrus
 PPC - Posterior Parietal Cortex
 M1 - Precentral Gyrus
 Frontal Lobe
 somatotopic organization
 M2 - Secondary Motor Cortex
 SMA - Supplementary Motor Area
 PM - Premotor Cortex ~
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PPC
Sensorimotor Pathways
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SMA
M1
PM
S1
PPC
Primary Motor Cortex
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Somatotopic organization
 neurons have preferred direction of
movement
Motor homunculus ~
M1: Coding Movement
Movement for limbs
 Neuron most active
 Preferred direction
 but active at 45 from preferred
 How is direction determined?
 Populations of M1 neurons
 Net activity of neurons with
different preferred directions
 vectors ~
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M1: Coding Movement
Implications
1. Most M1 active for every
movement
2. Activity of each neuron
1 “vote”
3. direction determined by
averaging all votes ~
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Motor Association Cortex
Motor area other than M1
 Premotor & Supplemental Motor Areas
 Active during preparation for movement
 Planning of movements
 Stimulation - complex movements
 motor programs
 Active during preparation for movement
 Planning of movements
 e.g. finger movements ~
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Motor Association Cortex
Active before movement
 Supplemental Motor Area
 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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SMA
M1
S1
PPC
PMA
Spinal cord
Planning Movements
Targeting vs trigger stimulus
 recording activity of neurons
 active when movement planned
 for specific direction
 Different populations of neurons active
 during planning (targeting)
 & execution (trigger stimulus) ~
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Simple finger flexion
 only M1 activation
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Sequence of complex finger movements
 M1 + SMA activation ~
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Mental rehearsal of finger movements
 only SMA activation ~
The Descending Spinal Tracts
Brain to Spinal Cord
Upper motor neurons
 communication with lower (a) motor
neurons
 Lateral pathway
 direct cortical control
 Ventromedial pathway
 brain stem control ~
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The Lateral Pathway
Voluntary movement
 distal limbs
 Corticospinal (Pyramidal) tract
 Primary pathway (> 1 million neurons)
 Contralateral control movement
 Cortico-rubrospinal tract
 Via red nucleus
 But some recovery if damage to
corticospinal ~
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Spinal Cord: Lateral Pathway
Dorsal
Ventral
Corticospinal
tract
Corticorubrospinal
tract
The Ventromedial Pathway
Neurons originate in brainstem
 Vestibulospinal & tectospinal tracts
 head & posture posture
 orienting responses
 Pontine & medullary reticulospinal tracts
 originate in reticular formation
 trunk & antigravity leg muscles
 tracts are antagonistic ~
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Major Descending Spinal Tracts
Motor Cortex
Lateral
Red
Nucleus
Ventromedial
Reticular
Nuclei
Spinal cord
Superior Colliculus
vestibular nuclei