Movement the motor system jun 13 2014
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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)


MPTP ?

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

…What is the mechanism?


MPTP ?

  • MPTP metabolized to MPP+ by MAO enzyme

  • MPP+ brought into cells – DA reuptake transporter

  • Selective for neurons in substantianigra

    • Neurotoxic


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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