PAS Motor 1

• Cortical motor areas and corticospinal tract

  • Cortical motor areas plan movement
  • Corticospinal tract sends plan to spinal cord lower motoneurons

  
• Upper motoneurons


  Plan movement

  
• Lower motoneurons


  Carry out movement by causing muscle contraction
• How Do We Move

  Nervous system has a BIG investment in the structures and connections that allow us to move, making it effortless for us
• Components of Body Movement

  • Motor Cortex
  • Brainstem
  • Spinal cord
  • Cerebellum
  • Basal Ganglia

  
• Motor Cortex


  • Involved in planning and executing movement
  • Sends signals to spinal cord via corticospinal tract

  
• Corticospinal tract


  Connects cortical motor areas with spinal cord lower motoneurons

  
• Upper and Lower Motoneurons

  1. Upper motoneurons create the movement plan

  2. Lower motoneurons carry out the plan and cause muscle contraction

  
• Lower motoneurons


  • Located in anterior horn of spinal cord
  • Receive excitatory signals from muscle spindles for stretch reflex
  • Muscle tone is regulated by descending components of motor system

  
• Upper motoneurons


  • Supply the message for movement
  • Regulate overall activity in the stretch reflex circuit

  
• Source of Upper Motoneurons

  • Precentral gyrus - Motor Cortex (MC)
  • Premotor Cortex (PMC)
  • Supplementary Motor Area (SMA)

  
• Motor Cortex (MC)


  • Stimulation causes contraction of small groups of muscles involved in simple movements
  • Small populations of neurons specify the direction and force for a movement

  
• Premotor Cortex (PMC)


  • Involved in planning of movement
  • Involved in movements utilizing sensory guidance
  • Stores learned movements

  
• Supplementary Motor Area (SMA)

  • Involved in planning movements
  • Communicates with SMA on opposite side for tasks that require both hands
  • Stores learned movements
• Lesions of Cortical Motor Areas

  • Motor Cortex Lesions cause weakness/paralysis on the opposite side of body
  • Premotor Cortex/Supplementary Motor Area Lesions cause inability to perform learned motor tasks, but without weakness or paralysis (Apraxia)

  
• Pathway to spinal cord - Corticospinal tract


  1. All cortical motor areas contribute to the corticospinal tract

  2. Corticospinal tract connects cortical motor areas with spinal cord lower motoneurons

  3. Travels down through corona radiata, internal capsule, brainstem, medulla/spinal cord junction - pyramidal decussation

  4. Most fibers cross to form Lateral Corticospinal Tract in spinal cord

  5. ~10% stay ipsilateral but cross later to form Anterior Corticospinal Tract
• Corticospinal Tract


  Also known as the pyramidal tract because its fibers form the pyramids of the medulla
• Cortico-Bulbo-Spinal Tract


  1. Travels with corticospinal tract from cortex

  2. Synapses on red nucleus and reticular formation in brainstem

  3. Axons from each nucleus form rubrospinal tract and reticulospinal tract that descend to spinal cord
• Red Nucleus and Reticular Formation


  • Upper motoneurons that modulate the activity of lower motoneurons

  
• Reticulospinal Tract


  Provides inhibition that reduces lower motoneuron activity and muscle tone
• Corticospinal Tract Lesions