Lecture Notes: Motor Pathways

Introduction to Motor Pathways

• Motor pathways are nerve pathways transmitting impulses from the brain to effectors.
• Also called descending pathways as they carry information from the CNS to the PNS.
• Output can cause muscle contraction or gland secretion.

Organization of Motor Pathways

• Originates from the motor cortex, descends through brain stem, and spinal cord to effectors.
• Different from sensory pathways (first, second, third order neurons) and divided into:
  • Upper Motor Neurons (UMN): Originate from cerebral cortex/brain stem.
    • Execute voluntary movements.
    • Regulate muscle tone, posture, balance.
  • Lower Motor Neurons (LMN): Originate from brain stem/spinal cord.
    • Project to skeletal muscles through cranial/spinal nerves.

Pathway Types

• Direct (Pyramidal) Pathways:
  • Extend from primary motor cortex.
  • Include corticospinal and corticobulbar tracts.
• Indirect (Extrapyramidal) Pathways:
  • Originate from other brain regions (basal nuclei, cerebellum, etc.).
  • Include rubrospinal, tectospinal, vestibulospinal, and reticulospinal pathways.

Direct Motor Pathways

• Corticospinal Pathways:
  • Conduct impulses to control limbs and trunk.
  • Two tracts:
    • Lateral Corticospinal Tract:
      • Decussate in medulla, control distal limbs.
      • Involved in precise movements (e.g., playing piano).
    • Anterior Corticospinal Tract:
      • Decussate in spinal cord, control trunk/proximal limbs.
      • Involved in larger, less precise movements.
• Corticobulbar Pathway:
  • Controls movements of the head.
  • Some axons decussate; others do not.
  • Involves cranial nerves, affecting eyes, tongue, neck.

Indirect Motor Pathways

• Rubrospinal Pathway:
  • Controls contralateral muscle movements in the distal parts of upper limbs.
• Tectospinal Pathway:
  • Controls reflexive movements of the head, eyes, trunk in response to stimuli.
• Vestibulospinal Pathway:
  • Controls ipsilateral posture and balance in response to head movements.
• Reticulospinal Pathways (Medial/Lateral):
  • Influence ipsilateral posture and muscle tone in response to body movements.

Summary

• Direct pathways originate in primary motor cortex; indirect pathways from other brain regions.
• Both pathways integrate to coordinate voluntary and reflexive movements.
• Understanding these pathways is crucial for grasping motor control mechanisms in the body.