Control of Movement

1
Control of Movement

• Lecture 19

2
Motor Systems

• Functions
• movement
• posture balance
• communication
• Guided by sensory systems
• internal representation of world self
• detect changes in environment
• external internal

3
3 Classes of Movement

• Voluntary
• complex actions
• reading, writing, playing piano
• purposeful, goal-oriented
• learned
• improve with practice

4
3 Classes of Movement

• Reflexes
• involuntary, rapid, stereotyped
• eye-blink, coughing, knee jerk
• graded control by eliciting stimulus
• Rhythmic motor patterns
• combines voluntary reflexive acts
• chewing, walking, running
• initiation termination voluntary
• once initiated, repetitive reflexive

5
Movement Muscles

• Movement occurs at joints
• Contraction relaxation of of opposing muscles
• agonists
• prime movers
• antagonists
• counterbalance agonists
• decelerate movement

6
Movement Muscles

• Movement control more than contraction
  relaxation
• Accurately time control of many muscles
• Make postural adjustment during movement
• Adjust for mechanical properties of joints
  muscles
• inertia, changing positions

7
Sensorimotor Integration

• Perceptual development
• Active interaction required
• environmental feedback important
• Held Hein (1950s)
• kittens passively moved
• depth perception deficits
• related responses, blinking, looming

8
Sensorimotor Integration

• Sensory inputs guide movement
• visual, auditory, tactile
• location of objects in space
• Proprioceptive vestibular
• position of our body
• Critical for planning refining movements

9
Error Correction Feedback

• During or after movement
• Compare actual position with intended position
• if different ----gt make correction
• muscle contractions
• Limited to slow movements

10
Error Correction Feed-forward

• Sensory events control movements in advance
• ballistic movements
• Prediction
• internal model of events
• e.g. catching ball
• representation of ball trajectory
• properties of musculoskeletal system
• Reevaluation after response completed

11
Sensorimotor Impairments

• Impaired proprioception ---gt motor deficits
• Large-fiber sensory neuropathy
• Aa Ab afferents degenerate
• proprioceptive tactile feedback
• Cant hold arm steady w/o visual input
• starts to drift after few seconds
• psuedo-athetosis

12
Sensorimotor Impairments

• Feed-forward control
• eyes open ballistic movements OK
• eyes closed
• ballistic movements highly inaccurate
• hand drifts at end of movement
• Eyes open only prior to movement
• errors greatly reduced
• lack of info about starting position

13
Organization of Motor Control

• Hierarchical Parallel
• Parallel
• pathways active simultaneously
• e.g. moving arm
• 1. muscles producing movement
• 2. postural adjustments during movement
• Recovery of function after lesion
• overlapping functions

14
Hierarchical Control of Movement

• 3 levels of control
• Spinal cord (SC)
• Brainstem
• Cortex
• Division of responsibility
• higher levels general commands
• spinal cord complex specific
• Each receives sensory input
• relevant to levels function

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Hierarchical Control Spinal Cord

• Automatic stereotyped responses
• reflexes
• rhythmic motor patterns
• Can function without brain
• Spinal interneurons
• same circuits as voluntary movement
• Pathways converge on a motor neurons
• final common path

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Hierarchical Control Spinal Cord

• Motor neurons in ventral horn
• Topographical organization of motor nuclei
• a.k.a. motor neuron pools
• longitudinal columns across 1-4 spinal segments
• according to 2 rules

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Topographical organization of motor nuclei

• Flexor-Extensor rule
• ventral extensors
• dorsal flexors

• Proximal-distal rule
• medial proximal muscles
• lateral distal muscles
• Parallel control systems
• proximal postural
• distal manipulative

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Hierarchical Control Brain Stem

• Modulates neurons in spinal cord
• interneuerons motor neurons
• 2 main parallel pathways
• Medial
• to ventromedial spinal cord
• postural / proximal muscles
• Lateral
• to dorsolateral spinal cord
• manipulative / distal muscles

19
Hierarchical Control Cortex

• 2 tracts
• Corticobulbar ---gtcranial nerves
• facial muscles
• Corticospinal ---gt spinal nerves
• Origin of axons
• 1/3 from primary motor cortex (M1)
• 1/3 from premotor areas
• 1/3 from somatosensory cortex

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Corticospinal Tract

• Direct control Indirect control
• Parallel pathways
• Direct ---gt spinal neurons
• Indirect control via
• cortico-reticulospinal tact
• cortico-rubrospinal tract

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Corticospinal Tract

• More parallel pathways
• Lateral corticospinal tract
• contralateral projections
• decussate at medullary pyramid
• distal muscles
• Ventral corticospinal tract
• ipsilateral projection
• proximal muscles

22
Effects of Lesions

• Motor cortex projections
• locus of damage determines deficit
• Cerebral Vascular Accidents (CVA)
• most common cause

23
2 classes of abnormal function

• Negative signs
• Loss of function
• e.g., weakness, loss of strength
• Positive signs
• stereotyped, abnormal responses
• release phenomena
• loss of normal inhibitory influences
• e.g., lesion of basal ganglia ---gt involuntary
  movements

24
Positive Signs Babinski Sign

• Lesion of corticospinal tract
• Plantar reflex
• Stroke firmly stroke sole of foot
• heel ---gt toe
• Normal flexion
• toe curl down
• Lesion Extension
• toes curl up and fan

25
Muscle Weakness

• Lesions produce different syndromes
• Lower motor neuron syndrome
• spinal motor neurons
• lesion soma or axon
• symptoms
• weakness
• fasciculations
• atrophy

26
Muscle Weakness

• Upper motor neuron syndrome
• descending motor pathways
• imbalance of excitatory/inhibitory interneurons
• symptoms
• spasticity occurs
• tonicity deep tendon reflexes
• atrophy is rare
• no fasciculations

27
Parallel Control Recovery

• Fractionation of movement
• independent control of single muscles
• via direct input from corticospinal tract
• Lesion in medullary pyramids
• can no longer grasp objects
• locomotion, posture unaffected
• Parallel pathways assume control

28
Parallel Control Recovery

• Monkeys If premotor outflow spared
• indirect control via brainstem
• strength returns
• but movement slow
• M1 ---gt lateral brainstem intact
• cortico-rubrospinal cortico-reticulospinal
  tracts assume control
• humans fewer fibers ---gt less recovery