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Movement & the Motor System Jun 13, 2014. SENSORIMOTOR CONTROL. From Sensory to Motor. Sensory info -- guide motor system Somatosensory, vestibular, visual Book works from the TOP to BOTTOM Sensory “ up”, motor “ down” Here -- SIMPLE to COMPLEX . Organization. HIERARCHY

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from sensory to motor
From Sensory to Motor
  • Sensory info -- guide motor system
    • Somatosensory, vestibular, visual
  • Book works from the TOP to BOTTOM
    • Sensory “up”, motor “down”
  • Here -- SIMPLE to COMPLEX
organization
Organization

HIERARCHY

  • Analogy to a corporation
    • Workers = muscles
    • Supervisors = spinal cord & brainstem
    • Quality control = basal ganglia & cerebellum
    • Manager = primary cortex
    • President/CEO = higher order cortex
muscles
Muscles
  • Skeletal muscle - stability to bony skeleton
  • Move around axes
  • 1000s of muscle fibers
    • “Fast” twitch fibers – speed
    • “Slow” twitch fibers – endurance
muscles1
Muscles
  • Innervated by motor neurons from spinal cord
    • ACh (neuromuscular junction)
  • Motor unit – motor neuron & muscle fibers
  • Receptors for proprioception
    • Ch. in length (stretch), tension
muscles2
Muscles
  • Only actively contract - more than one direction depends on antagonistic pairs
    • Contraction/relaxation
    • Ex. biceps & triceps
  • Flexorsbend, extensorsstraighten
spinal cord
Spinal Cord
  • Via motor neurons
  • Sensory feedback from muscle & somatosensory
  • Can be independent of the cortex
    • Basic reflex circuits
    • Copy of information to cortex
    • Quick, unconscious
basic motor reflexes
Basic Motor Reflexes

Withdrawal reflex

Sensory info  spinal cord  motor response

“Walking” reflex

In response to foot contact, ankle rotation

Infants

basic motor reflexes1
Basic Motor Reflexes

Stretch reflex

  • After sudden stretching force
  • Muscle stretch receptor  spinal cord muscle
  • Compensatory contraction
  • Controls external force on body position

Infant reflexes

  • Sucking, rooting, grasping, startle
basic motor reflexes2
Basic Motor Reflexes
  • Requires info to muscle contracting, antagonist, and contralateral
    • Adjust and coordinate both sides
reflexes
Reflexes
  • Some directed by brainstem
    • Eye movements (saccades, smooth pursuit)

Complex movement under control of the cortex and descending motor pathways

primary motor cortex
Primary Motor Cortex

Most “movement” requires cortical control

Cortex to motor neurons (spinal cord) & brainstem

Directed movement, interaction with the environment

primary motor cortex1
Primary Motor Cortex
  • Pre-central gyrusof frontal lobe
    • Adjacent to somatosensory area (post-central gyrus)
    • Why is this relevant?
  • Homunculus
    • Fingers, tongue, face – fine motor control
descending pathways
Descending Pathways
  • Several tracts
  • Different tracts/locations  different motor deficits
  • Control of posture/whole body movements vs. limb movements
descending pathways1
Descending Pathways

Dorsolateral corticospinal tract

  • Distal muscles (limbs, hands, fingers, etc.)
  • Primary motor cortex medulla (crossover)  spinal cord  muscles
descending pathways2
Descending Pathways

Three other tracts…

  • Indirect to spinal cord
  • Synapse w/ cranial nerve motor info
  • Proximal trunk muscles

1o cortex receives info from secondary motor cortex

basal ganglia
Basal Ganglia
  • Interconnected nuclei
  • Communicates w/ midbrain, rest of cortex
  • Distribution of tone, coordinating muscle groups
    • Shifting weight, posture
  • Cognitive roles
    • Compulsion, motivation, reward
cerebellum
Cerebellum
  • Comm. w/ cortex, basal ganglia, brainstem
  • Corrects movements, motor errors
    • Based out output
  • Rapid movement req. fine control, adapting to changing conditions
  • Also has cognitive roles
secondary motor cortex
Secondary Motor Cortex

Premotor cortex

  • Frontal lobe
  • To primary motor
  • Decisions, coordination, programming of motor plans (sequence of events)
    • Order of movements, patterns
    • Imagining action
secondary motor cortex1
Secondary Motor Cortex
  • Complex integration of secondary areas
    • Input about target, body position
  • Mirror neurons – observation of motor action
    • Social learning & cooperation
  • Input from association cortex (in prefrontal cortex)
association cortex
Association Cortex
  • Dorsolateral prefrontal cortex
  • Project to premotor area
  • Control over motor system
    • Directing attention, eye movements
    • Decision to make movements
    • Sensory feedback
association cortex1
Association Cortex
  • General programs stored, adapted to situations
  • Can be developed w/out practice
  • Can be modified w/ practice
    • Group behaviors together
    • Shift control to lower hierarchy (less cortex)
motor dysfunction
Motor Dysfunction

At any point in the hierarchy

  • Muscle weakness, atrophy, paralysis
    • Communication betw. spinal cord & motor unit
  • Descending pathways
    • Motor control, coordination, etc.
    • Cerebellar or basal ganglia disorders
motor dysfunction1
Motor Dysfunction
  • Apraxia – dysfunction in voluntary movement
    • Not due to muscle, comprehension, motivational deficit
  • Reappearance of infant reflexes w/ cortical damage (withdrawal, grasping)
    • Don’t “outgrow” them, inhibited w/ development
huntington s chorea
Huntington’s Chorea
  • Basal ganglia & cortex
  • Genetic case - autosomal dominant
    • 30-50 years old
    • Protein damages neurons, over-stimulates target cells
    • Death of neurons
  • Severe cognitive, motor dysfunction
  • Jerks, twitches, writhing (dancing movements)
parkinson s disease
Parkinson’s Disease
  • Death of neurons proj. to basal ganglia
    • Substantianigra
  • Rigidity, tremor, slowed movement; cognitive
  • Starting, stopping voluntary motion
  • Genetic, environmental causes
parkinson s disease1
Parkinson’s Disease

Treatment – replace DA

  • DA can’t cross BBB
  • L-Dopa to replace DA
  • Neurons continue to die
  • Serious side effects
the frozen addicts
The Frozen Addicts

Awakening the Frozen Addicts (BBC, 1993)

http://youtu.be/QJIMC9d9l2o

MPPP (synthetic opioid)

slide49
MPTP

Ingestion of MPTP causes severe, immediate Parkinson’s symptoms…

…What is the mechanism?

slide50
MPTP
  • MPTP metabolized to MPP+ by MAO enzyme
  • MPP+ brought into cells – DA reuptake transporter
  • Selective for neurons in substantianigra
    • Neurotoxic
slide51
MPTP
  • Implications for control of movement?
    • SN projects to basal ganglia (putamen/caudate)
  • Animal models
    • Primates
    • Some rodents (rats are immune)
  • MPP+ toxicity as a natural cause of Parkinson’s?
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