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)