Pyramidal and Extrapyramidal Tracts: Key Concepts

Overview

• Motor Signals Pathway: For muscle movements such as flexing a bicep, the brain and brainstem send motor signals via the spinal cord.
• Two Main Tracts: Pyramidal and extrapyramidal tracts involved in carrying these signals.

Pyramidal Tracts

• Components: Composed of upper motor neurons directly innervating lower motor neurons in the spinal cord.
• Function: Primarily responsible for voluntary movement control.
• Sub-divisions:
  • Corticospinal Tract:
    • Originates in the motor cortex.
    • Lateral Corticospinal Tract:
      • Comprises 90% of fibers which cross at the medulla (pyramidal decussation).
      • Controls limb muscles.
    • Anterior Corticospinal Tract:
      • Comprises 10% of fibers which do not cross at the medulla.
      • Controls trunk muscles.
  • Corticobulbar Tract:
    • Starts in the motor cortex and travels alongside the corticospinal tract.
    • Directly synapses with cranial nerve nuclei (V, VII, XI, XII) in the brainstem.
    • Some fibers branch to both ipsilateral and contralateral nuclei (e.g., chewing and neck muscles).
• Pathway:
  • Neurons travel through internal capsule to the brainstem, forming medullary pyramids.
  • Synapse on lower motor neurons in the anterior horn of the spinal cord.

Extrapyramidal Tracts

• Function: Coordinates muscle movement by indirectly influencing lower motor neurons via interneurons.
• Characteristics:
  • Do not directly start from the cerebral cortex.
  • Upper motor neurons are located in brainstem nuclei.
  • Involved in the control and coordination of movement.

Additional Details

• Higher Order Functions: Involves various brain functions including attention, consciousness, emotion, language, learning, memory, and stress.
• Associated Systems: Related to the autonomic nervous system, basal ganglia, cerebellum, and more.

Summary

• Pyramidal Tracts: Essential for voluntary motor function, directly innervating lower motor neurons.
• Extrapyramidal Tracts: Facilitate movement coordination through indirect pathways.

References

• Medical textbooks and journals for detailed anatomy and physiology insights.

This summary provides a high-level overview for students studying the neural pathways involved in motor control, specifically focusing on the roles of pyramidal and extrapyramidal tracts in voluntary and coordinated movements.