bn20 cortical motor control ppt 2384

8/3/2019 Bn20 Cortical Motor Control Ppt 2384

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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

bn20 cortical motor control ppt 2384

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