• voluntary movement is the only way to express who we are
  • voluntary muscles are striated
    • exception: heart striated muscles are not voluntarily controllable
    • heart requires no input from motor neurons to contract
  • voluntary muscles are also called striated muscles

  • some voluntary muscles can only be actuated in groups

  • voluntary movement system
    • muscle and motorneuron types
    • reflexes
    • automatic, stereotype movements
    • self-expression movements
  • movement types
    • reflexes
      • hot stove reaction
      • stumble recovery
      • knee-jerk reaction to hammer bump
    • stereotype movements
    • self-expression

motor hierarchy

  • going bottom-up, the hierarchy is as follows
    • skeletal muscle
    • motorneurons CNS
    • motor interneurons
    • central pattern generators
    • brainstem motor control centers
    • cortical motor control centers
  • as one goes up the hierarchy, there is more meaning and intention
    • movements become an action as more intent is imbibed in it
  • at the bottom layers, there is no inherent self expression

reflexes

  • handled by
    • skeletal muscle
    • motorneuron CNS
    • motor interneurons
  • twitches

stereotype movements

  • i.e. urinating and defecating handled by
    • central pattern generators
  • simple movements

self expression

  • cortical motor control centers handle
    • reaching out
    • talking
    • dancing
    • writing
  • complex movements

problems with motor hierarchy

lower level

  • motorneurons CNS breakage - Polio is an example
  • neuromuscular problems - myasthenia gravis with drooping eyelid
    • junctions between the nerves and the muscles

  • perepheral neuropathy - gwillian barre affected nerves betwrrn motorneuron CNS and skeletal muscle

  • reflexes cannot happen
  • stereotypical movements cannot happen

  • actions cannot happen

  • if motorneurons are gone, then complete paralysis
    • no movement occurs
    • flaccid paralysis
  • with disuse, muscles tend to flaccid and eventually atrophy

higher level

  • stroke in primary motor cortex
    • reflexes happen, but lower level motions are exaggerated
    • stereotypical movements like walking and chewing can happen, not smooth motion
    • but no access to voluntary movements
  • motor neurons do not talk back to the cortex due to the stroke
    • the top talk to the underlings but the underlings dont talk back to the top

motor modulation

  • cerebellum is the orchestral conductor for the muscles working well together
    • cerebellum is the motor modulator
    • it doesnt talk directly to motor neurons
    • it handles action selection
  • it is a modulatory pathway and not a part of the hierarchy
    • it only talks to the top three parts of the hierarchy
      • central pattern generators
      • brainstem motor control centers
      • cortical motor control centers
  • cerebellum get input from
    • skin and muscle
    • motor hierarchy about intent
  • when the cerebellum modulation doesnt work, they have ataxia
    • dysmetria is a subset of not being able to target something
    • muscles cannot be smoothly stopped on target
      • decomposition of movement occurs