~bn20 cortical motor control.ppt
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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 ~
Sensorimotor Cortical System
Integration of sensory information and directed movements
Anatomy Descending spinal tracts
Lateral pathway Pyramidal Motor System
Ventromedial pathway Extrapyramidal pathway ~
Cortical Anatomy 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 ~
M1
SMA
S1
PM
PPC
M1 S1
PM
SMA
PPC
Prefrontal
Sensorimotor Pathways
Primary Motor Cortex
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 ~
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 ~
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 ~
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 ~
M1 S1
PMA
SMA
Spinal cord
PPC
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) ~
Simple finger flexion only M1 activation
Sequence of complex finger movements M1 + SMA activation ~
Mental rehearsal of finger movements only SMA activation ~
The Descending Spinal Tracts
Brain to Spinal Cord
Upper motor neurons communication with lower () motor
neurons Lateral pathway
direct cortical control Ventromedial pathway
brain stem control ~
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 ~
Dorsal
Ventral
Spinal Cord: Lateral Pathway
Corticospinal tract
Cortico-rubrospinal 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 ~
Major Descending Spinal Tracts
Motor Cortex
Spinal cord
Red Nucleus
Reticular Nuclei
Superior Colliculusvestibular nuclei
VentromedialLateral
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