Motor hierarchy

III. Classification of Voluntary Movements (Continued):

• Reflexes:
  • Defined by:
    • Involuntary responses to stimuli.
    • Not requiring conscious thought or intention.
    • Examples:
      • Knee jerk reflex
      • Withdrawal reflex from hot objects
      • Stumble reflex
  • Occur at lower levels of the motor hierarchy without needing the brain.
  • Involve motor neurons stimulating skeletal muscles for contraction.

Stereotyped Automatic Movements:

• Defined by:
  • Repetitive, learned movements performed frequently.
  • Examples:
    • Chewing
    • Walking
    • Running
    • Standing
    • Vomiting (though less frequent)
  • Produced by central pattern generators (CPGs) in the spinal cord and brainstem.
  • CPGs are neural circuits that generate rhythmic patterns without extensive cortical input.

Movements of Self-Expression:

• Defined by:
  • Intentional and purposeful movements.
  • Driven by the cortical motor control centers.
  • Examples:
    • Reaching
    • Talking
    • Fine motor skills (picking food out of teeth, writing)
    • Dancing

Motor Hierarchy:

• The lecture introduces the concept of the motor hierarchy, a layered system controlling movement complexity.

  • Lower levels (motor neurons and spinal cord) generate basic movements.
  • Higher levels (brainstem and cortex) add complexity, intention, and meaning.

• A simple twitch is produced by motor neuron excitation.

• Central pattern generators create basic rhythmic movements.

• Brainstem motor control centers enable more complex movements like walking and posture.

• Cortical motor control centers are responsible for intentional movements with meaning and purpose.

• Neocortex involvement imbues movement with intention and transforms it into action. Key Points:

• Reflexes, stereotyped movements, and movements of self-expression are distinct categories based on control level and intentionality.

• The motor hierarchy plays a crucial role in coordinating movement complexity.

• Cortical involvement adds meaning and purpose to movement, transforming it into action.

Note:

• This section expands on the three movement categories and introduces the motor hierarchy concept.

Problem with Motor hierarchy Motor Modulation