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The Motor Systems

The Motor Systems. What’s the motor system?. Parts of CNS and PNS specialized for control of limb, trunk, and eye movements Also holds us together From simple reflexes (knee jerk) to voluntary movements (96mph fast ball) Remarkable: Muscles only contract. Plan.

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The Motor Systems

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  1. The Motor Systems

  2. What’s the motor system? • Parts of CNS and PNS specialized for control of limb, trunk, and eye movements • Also holds us together • From simple reflexes (knee jerk) to voluntary movements (96mph fast ball) • Remarkable: Muscles only contract

  3. Plan • Components of the motor systems • Basic principle of movement control • What is helpful for understanding basic motor system organization • Motor programs • Descending motor pathways

  4. Cortical motor areas Basal ganglia Cerebellum Descendingcortical motor paths Descendingbrain stem paths Spinal cord: Intermediate zone Ventral horn MotorSystems Motor systems Muscle

  5. Functional Hierarchy of Motor Paths Motor execution: force & direction

  6. Parallel Organization Basal ganglia Cerebellum

  7. Motor Cortical areas Internal capsule from Basal ganglia from Cerebellum

  8. Organization of Movements • Diverse & adaptive • Hierarchical: 3 major types • Reflexes • Postural adjustments • Voluntary movements

  9. Organization of Movements • Hierarchical: 3 major types • Reflexes Spinal cord circuits • Postural adjustments Spinal & Brain stem • Voluntary movements Spinal cord, Brainstem, and cortex Postural adjustments & voluntary movementsdepend more on cerebellar and basal gangliafunction than reflexes

  10. Reflexes • Stimulus-evoked involuntary muscle contraction • Monosynaptic (+) reflex • Knee-jerk • Jaw-jerk

  11. Knee Jerk From musclestretch receptors to muscle

  12. Reflexes • Stimulus-evoked involuntary motor muscle contraction • Monosynaptic (+) reflex • Knee-jerk • Jaw-jerk • Disynaptic reflex (+) • withdrawal

  13. Why Disynaptic? • Greater control (gate) • Very simple context • More complex response

  14. Greater control: Spinal Circuits from periphery from highercenters Response inhibitedby inhibition to muscle

  15. Greater control: Spinal Circuits from periphery from highercenters Response blockedby inhibition to muscle

  16. Motor I/O Knee-jerk Automaticpostural adjustments • Balance • Limb support • Flexible than reflexes • Constrained than voluntary

  17. Postural adjustments • Context important • Maintain balance--supported v/s unsupported • Feedback control-reactive • Error correction • Response lags stimulus; sometimes too late • Feed-forward control-predictive • Response anticipates stimulus • More timely, but depends on internal models • Practice, learning

  18. Voluntary movements • Organized around purposeful acts • Flexible input-output relationships • Limitless • Price to pay: whole brain

  19. Motor I/O Knee-jerk Automaticpostural adjustments Voluntarymovement

  20. Voluntary movements • Organized around purposeful acts • Flexible input-output relationships • Limitless • Price to pay: whole brain Discuss: • Goal representation • Motor program

  21. The goal of voluntary movements is represented… somewhere • Motor equivalence • Individual motor actions share important characteristics even when performed in different ways • Abstract representation; effector independent • Hand writing • Soccer • Goal representation

  22. Voluntary movements are organized by motor programs • Translate goal into action • Formation of a movement representation, or motor program • Program • To produce the desired goal, which muscles should contract and when • 2 Key movement characteristics • Spatial (hand path; joint angles) Kinematic plan • Forces/loads Dynamic plan • All accomplished by contracting muscles

  23. Kinematic & Dynamic Plans • Reach to target • Straight hand path • Reach up • Against gravity • More force to achieve goal • Reach down • Gravity assists • Less force to achieve goal • Kinematic and dynamic representations of upcoming movement

  24. Summary • Motor behavior hierarchy • Reflexes • Postural adjustments • Voluntary movements • Internal representations • Reflexes and postural adjustments--simple; invariant • Voluntary movements--complex; flexible • Voluntary movements • Kinematic and dynamic representations • Goal representation • Motor hierarchy • spinal, brain stem, cortical motor circuits • Descending motor pathways

  25. Cortical motor areas Descendingcortical motor paths Descendingbrain stem paths Spinal cord: Intermediate zone Ventral horn MotorSystems Motor systems 1° motor cortex Premotor cortex Red nucleusReticular formationVestibular nuclei Superior colliculus Muscle

  26. Indirect Direct Motor Pathways Hierarchy Premotorareas Motor Pathways Hierarchy

  27. From brain Segmental interneuron Motor neuron Spinal Motor Columns Short Long Propriospinal-- Intersegmental-- neurons Motor columns (motor neurons)

  28. Lateral pathways: limb control Ventral HornOrganization:Proximal - distal rule Medial pathways: trunk control

  29. Tectum Red nucleus Reticularformation Vestibularnuclei Tectospinaltract Reticulospinaltracts Rubrospinal tract Vestibulospinaltracts Brain Stem Motor Paths Medial Lateral

  30. Brain Stem Pathways • Lateral • Rubrospinal tract: distal limb control; crude • Medial • Tectospinal tract: eye-head coordination • Reticulospinal tract: automatic postural adjustments and movements (hip; shoulder) • Vestibulospinal tract: balance (axial muscles); automatic postural adjustments

  31. Brain stem nuclei Superior colliculus Tectospinal tract Red nucleus Rubrospinal tract Vestibular nuclei Vestibulospinal tracts Reticular formation Reticulospinal tracts

  32. Vestibular & Reticular nuclei Red nucleus Rubro- spinal tract Medialbrain stempaths Medial Lateral CorticalMotor Paths Pyramidal X LateralCortico-spinaltract Ventralcorticospinaltract

  33. Cortical Motor Areas

  34. Primary motor PMC Lateral and ventral CST Corticobulbar tract Lateral Brain View

  35. SMA Primary motor CMA Lateral and ventral CSTs Corticobulbar tract

  36. Why bother study the motor pathways? • Anatomical substrates: How it works • Multiple parallel paths & diversity of spinal connections • Damage to 1° motor cortex and pre-motor cortex projections recover some lost functions • Damage to cortex and brain stem paths recover some lost functions • Loss of direct connections and alternate paths can recover some lost functions

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