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Motor system basics

Motor system basics. Development. Motor neurons & Muscle fibers. Local motor control. Muscle spindles enforce the “stretch reflex”: feedback about muscle length. Golgi tendon provide feedback about level of force. Spinal chord. Central pattern generators.

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Motor system basics

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  1. Motor system basics

  2. Development

  3. Motor neurons & Muscle fibers

  4. Local motor control Muscle spindles enforce the “stretch reflex”: feedback about muscle length. Golgi tendon provide feedback about level of force.

  5. Spinal chord

  6. Central pattern generators Taking care of the basic simple functions...

  7. Central pattern generators

  8. Central pattern generators Decerebratewalking cat

  9. Central pattern generators Decerebratewalking cat

  10. Cortical control

  11. Postural control Vestibular and Reticular nuclei (medial motor system). Adaptation and Anticipation – Sailor “sea legs”

  12. Voluntary control • Cortico-spinal and Rubro-spinal pathways (lateral motor system). • Fine motor control. • ~ 1 Million fibers originating in: • Primary motor cortex (one third) • Premotor cortex (one third) • Somatosensory cortex (one third)

  13. Motor system hierarchy

  14. Motor system hierarchy Performing actions is complicated… Incorporate: Visual information Auditory information Somatosensory information Make a decision Make a motor plan (timing, forces, balance, etc…) Execute

  15. Somatotopic organization of M1

  16. Encoding of M1 neurons: Force

  17. Encoding of M1 neurons: Direction Textbook stories describe M1 neurons as responsible for the final motor execution step…

  18. Higher motor levels Visual – movement performed according to cue. Internal – movement performed as part of a memorized sequence.

  19. Anterior parietal & Premotor cortex Visuomotor coordination Object manipulation Grasping

  20. Areas F5 and AIP/PF Canonical neurons – object specific actions Regardless of where objects are located Murata (1997, 2000)

  21. Microstimulations Story is a bit more complex. Long microstimulations in premotor, anterior parietal, and primary motor cortex generate complicated multi-effector movements. Like grasp to eat… Idea of motor primitives

  22. Supplementary motor cortex Neurons that respond to a specific movement only when it is part of a sequence (a) or to any movement, but only according to its location in the sequence (b).

  23. Functional specialization Damage in M1 creates weakness in the relevant part of the body. Damage in parietal and premotor cortex creates problems with movement planning and coordination. Damage in SMA creates problems with learning new movement sequences

  24. Motor control What is the purpose of the motor system?

  25. Encoding space Head centered? Hand centered? Eye centered?

  26. Inverse model You need to translate external space to internal space…

  27. Inverse model Eventhough you use different joints and muscles for different movements: Movements remain straight, smooth, with symmetric velocity profile. Your motor system cares about making smooth efficient movements in external space… (Morasso 1981)

  28. Motor primitives Invariance to scale…

  29. Motor primitives Invariance to effector… Raibert1977

  30. Inverse model is flexible… (Brashers-Krug, Shadmehr, and Bizzi1996)

  31. Inverse model is flexible…

  32. Motor memory

  33. Where does motor learning happen?

  34. How do we study neurophysiology?

  35. Dendrites Cell body Axon

  36. Neural activity

  37. In vitro electrophysiology Control > ASD

  38. In vivo electrophysiology Control > ASD

  39. In vivo electrophysiology Control > ASD Anesthetized or awake

  40. Electrode location Control > ASD

  41. Magnetic resonance imaging (MRI)

  42. Anatomy - Separating tissues 1T 2T

  43. Anatomy – Cortical thickness

  44. Anatomy – Cortical folding

  45. Anatomy – white matter Tractography Fiber volume Fiber length

  46. Brain function Neurovascular coupling

  47. Vasculature

  48. Changes in oxygenated blood זמן Heeger et. al. 2002

  49. fMRI experiment

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