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Introduction to the Motor Systems

Introduction to the Motor Systems. John H. Martin, Ph.D. Center for Neurobiology and Behavior. Plan. Components of the motor systems Focus on spinal control of limbs and trunk Same principles apply to to head control via brain stem Basic principles of movement control

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Introduction to the Motor Systems

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  1. Introduction to the Motor Systems John H. Martin, Ph.D.Center for Neurobiology and Behavior

  2. Plan • Components of the motor systems • Focus on spinal control of limbs and trunk • Same principles apply to to head control via brain stem • Basic principles of movement control • What is helpful for understanding basic motor system organization • Motor programs for voluntary movement • Descending motor pathways

  3. Cortical motor areas Basal ganglia Cerebellum Descendingcortical motor paths Descendingbrain stem paths Spinal cord: Intermediate zone Ventral horn MotorSystems Motor systems PNS Fig. 33-12 Muscle

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

  5. Parallel Organization Association & limbic cortex Basal ganglia Cerebellum

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

  7. Hierarchical & Parallel Organization of the motor systems • Top down organization of the motor pathways--opposite that of sensory paths • Subcortical motor centers--cerebellum & basal ganglia--access cortical motor areas via the thalamus (not just sensory) • Organization of multiple subcortical and cortical motor circuits-reminiscent of parallel sensory pathways

  8. Organization of Movements • Hierarchical: 3 major types • Reflexes • Postural adjustments • Voluntary movements • …from simple to complex • Diverse & adaptive • Purposeful

  9. Organization of Movements • Hierarchical: 3 major types • Reflexes Spinal cord circuits • Postural adjustments Spinal & Brain stem • Voluntary movements Spinal cord, Brainstem, & cortex Postural adjustments & voluntary movementsdepend more on cerebellar and basal gangliafunction than reflexes Dual purpose: 1) upcoming lectures; 2) context for motor pathways

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

  11. Knee Jerk From musclestretch receptors Ventralhorn to muscle

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

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

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

  15. Motor I/O Knee-jerk Automaticpostural adjustments • Balance • Limb support • Flexible than reflexes (greater #; each w/control) • Constrained than voluntary

  16. Postural adjustments • Context important • Can reorganize depending on context • Feedback control-reactive • Error correction • Response lags stimulus; sometimes too late; sometimes vicious circle • Feed-forward control-predictive • Response anticipates stimulus • More timely, but depends on practice • Depends on cerebellum,brain stem pathways & spinal cord • More complex neural representation

  17. Voluntary movements • Organized around purposeful acts • Flexible input-output relationships • Limitless • Price to pay: whole brain • Recruits all motor systems components & much of the association cortex Discuss: • Goal representation • Motor programs

  18. 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 • ??Association & Premotor cortex

  19. Voluntary movements are organized by motor programs • Translate goal into action • Formation of a movement representation, or motor program • ??Premotor cortex --> Primary motor cortex • Program • To produce the desired goal, which muscles should contract and when • 2 Key movement characteristics that are programmed • Spatial (hand path; joint angles) Kinematic program • Force Dynamic program

  20. Kinematic & Dynamic Programs in Reaching • Reach to target--(Sensation to Action) • Visual cortex-->Association cortex-->Premotor-->1° motor • Distinct kinematic and dynamic programs • Reach up • Against gravity • More force to achieve goal • Reach down • Gravity assists • Less force to achieve goal • Flexible control

  21. Summary • Motor behavior hierarchy • Reflexes • Postural adjustments • Voluntary movements • Internal/neural representations • Reflexes simple; invariant • Postural adjustments • Voluntary movements complex; flexible • Voluntary movements • Goal representation • Kinematic and dynamic programs • No wonder why voluntary movement recruit entire motor system

  22. Cortical motor areas Descendingcortical motor paths Descendingbrain stem paths Spinal cord: Intermediate zone Ventral horn MotorPathways Motor systems 1° motor cortex Premotor cortex Red nucleusReticular formationVestibular nuclei Superior colliculus PNS Fig. 33-12 Muscle

  23. Indirect Direct Origins of motor paths Motor Pathways Hierarchy Premotorareas Motor Pathways Hierarchy

  24. Premotorareas Motor Pathways Hierarchy

  25. Premotorareas Motor Pathways Hierarchy

  26. Premotorareas Motor Pathways Hierarchy

  27. Premotorareas Motor Pathways Hierarchy

  28. Motor pathways organized around the motor nuclei

  29. From brain Segmental interneuron Motor neuron Spinal Motor Columns Short Long Propriospinal-- Intersegmental-- neurons Motor columns (motor neurons) PNS Fig. 33-13

  30. Lateral pathways: limb control Ventral HornOrganization:Proximal - distal rule Medial pathways: trunk control NTA Fig. 10-2

  31. Tectum Red nucleus Reticularformation Vestibularnuclei Tectospinaltract Reticulospinaltracts Rubrospinal tract Vestibulospinaltracts Bilateral Contralateral Brain Stem Motor Paths Medial Lateral PNS Fig. 33-14

  32. Brain Stem Pathways • Lateral • Rubrospinal tract: distal limb control; crude(red nucleus) • Medial • Tectospinal tract: eye-head coordination (superior colliculus) • Reticulospinal tract: automatic postural adjustments and movements (hip; shoulder)(reticular formation) • Vestibulospinal tract: balance (axial muscles); automatic postural adjustments (vestibular nuclei)

  33. Vestibular & Reticular nuclei Red nucleus Rubro- spinal tract Medialbrain stempaths Bilateral Contralateral Medial Lateral CorticalMotor Paths Pyramidal X LateralCortico-spinaltract Ventralcorticospinaltract PNS Fig. 33-15

  34. Cortical motor paths • Lateral corticospinal tract • Limb control mostly • Ventral corticospinal tract • Proximal muscle control; mostly upper body • For cranial muscle control: Corticobulbar tract • with medial and lateral components

  35. Origins of cortical motor paths • Primary motor cortex • Premotor cortex • Supplementary motor area (SMA) • Cingulate motor area (CMA)

  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 • With spinal cord injury. loss of monosynaptic connections and alternate paths via segmental and intersegmental interneurons can recover some lost functions

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