Lecture Notes: Rubrospinal Tract

Introduction

• Continuation of the series on descending tracts.
• Focus on the rubrospinal tract in this lecture.

Origin of the Rubrospinal Tract

• Begins in the red nucleus, located in the midbrain.
• Associated structures:
  • Midbrain, pons, medulla, spinal cord, cerebral cortex, cerebellum.

Function of Red Nuclei

• Primarily involved in the activation of flexor muscles.
• Believed to supply upper limb flexors.
• Research suggests it maintains lower limb flexors through an unclear mechanism.

Stimulation of Red Nuclei

• Cerebral Cortex:
  • Contributes fibers (cortical rubral fibers) for stimulation.
  • Involves primary motor cortex, premotor cortex, and supplementary motor area.
• Cerebellum:
  • Through deep cerebellar nuclei: globose and emboliform nuclei.
  • Provides unconscious proprioceptive information.

Pathway

• Decussation:
  • Occurs in the midbrain at the ventral tegmental decussation.
  • Fibers cross to the contralateral side.
• Descent:
  • Travels down to the lateral white column of the spinal cord.
  • Assists the lateral corticospinal tract.

Termination and Function

• Influences alpha and gamma motor neurons in the anterior gray horn.
  • Alpha neurons: Affect extrafusal muscle fibers.
  • Gamma neurons: Maintain tension in muscle spindles.
• Affects flexor muscles, primarily in the upper limbs.
• Recent findings suggest a regulatory role on lower limb flexors.

Summary

• The rubrospinal tract is essential for stimulating upper limb flexors and potentially regulating lower limb flexors.
• Key stimuli are from the cerebellum and cortical rubral fibers.
• Crosses at the midbrain and descends with the lateral corticospinal tract.

Upcoming Topics

• Next lecture will cover the medullary reticulospinal tract.
• A complete overview of descending tracts will follow.

Note: These notes summarize the key points from the lecture on the rubrospinal tract, covering its origin, pathway, function, and associated research findings. Use this guide to review the fundamental concepts discussed in class.