Movement and the Motor System (Chapter 5b)

Initiation of Movement:

  • Frontal lobes
    • Prefrontal::planning of movement
    • Premotor::organize motor sequences
    • Primary::produce specific movements
  • Support w/neuroimaging - sensation and motor bands, supporting motor areas

Components:

  • Upper and lower motor neurons::movement of Actin and Myosin along the muscle fibers, causing contraction of muscle
  • Neuromuscular junction and ACh
  • Decassation of the medulla (just like somatosensory cortex)

Corticospinal Tracts:

  • Topographic map associated w/the spinal cord
  • Lateral corticospinal tract::moves limbs and digits
  • Ventral corticospinal tract::moves muscles of midline of the body
  • Interneurons project to motor neurons - motor neurons project to muscles of the body

The Spinal Cord:

  • Divided into different segments
    • Cervical region::hands and arms
    • Lumbar::legs
    • Thoracic::trunk/organs
  • Quadriplegia::leg and arm paralysis above C4
  • Paraplegia::leg paralysis; damage to thoracic and lumbar segments
  • Paralysis patients a real driving force behind stem cell work
    • Stem cells = dirty word in neuroscience
    • Pluripotent stem cells
    • Adult cells are collected from the patient and reprogrammed and derived to the affected cell types (endothelial, muscle, etc)

The Brainstem and Species-Typical Movement:

  • Coding of species-specific unconscious behaviors
  • Derived from the brainstem
  • Ex: flailing before a fall, chest puff after being threatened, facial expressions

Mirror Neurons:

  • Active during preparation of a movement; active while watching someone else perform a similar movement
    • Empathize with emotions that someone else is having
  • May be important for understanding, identifying, and imitating other people; may be involved in social behaviors
  • Unknown whether they cause or result from social behavior
  • Located in the parietal lobes and the dorsal lateral prefrontal cortex

The Basal Ganglia:

  • Allows us to adjust force of our movements
  • Inputs - motor cortex, premotor cortex, prefrontal cortex, substantia nigra
  • Outputs - motor cortex, substantia nigra
  • Caudate/putamen::input from cortex, output to globus pallidus
  • Globus pallidus::connect to and inhibits the thalamus
  • Basal ganglia selects a movement to make by ceasing to inhibit it

Damage to the Basal Ganglia:

  • Caudate/putamen
    • Hyperkinetic::too much movement
    • Huntington’s Chorea::uncontrollable flailing motions; doesn’t appear until your 40s; always fatal about 7-10 years after diagnosis
    • Tourette’s Syndrome::bodily tics
  • Substantia nigra
    • Hypokinetic::too little movement
    • Parkinson’s Disease::inability to initiate movement over time

Cerebellum:

  • Essential for acquiring and maintaining motor skills - practice and precision
  • About 20% of brain volume and 1/2 of all neurons
  • Damage
    • Midline::balance, eye movement, upright posture, walking
    • Lateral::arm, hand, finger movements
  • Movement control
    • Timing of movements (metronome and tapping)
    • Movement accuracy (throwing darts)

Repair, Regeneration, and Recovery:

  • What is recovery?
    • Complete return of function vs marked improvement in function vs degree of improvement
    • Question of compensation - brain damage usually improved
  • Factors likely to influence recovery in CNS
    • Severity, #, spacing of insults
    • Age at time of insult
    • Extent to which function can be taken over by another
    • Extent/quality of rehabilitation
    • Difference in brain structure
    • Overall brain integrity
    • Motivation/emotional factors
  • Peripheral nerve regeneration
    • Henry Head
    • Superficial radial nerve and external cutaneous nerve
    • Protopathic vs. Epicritic
    • Hot and cold - 7wks
    • Light touch - 1yr
    • Schwann cells will come into damage area and guide axon (like orange barrels on highway)

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