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
  • $Latera$l::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)