Lecture on Descending Tracks

Overview

• Focus on corticospinal tracts
• Discussion on descending tracks, including other types in separate videos (e.g., rubrospinal, vestibulospinal, etc.)
• Corticospinal tracts: Two types
  • Lateral corticospinal tract: Controls distal limb musculature
  • Anterior (ventral) corticospinal tract: Controls axial musculature

Corticospinal Tract Details

Basic Anatomy

• Originates in the cortex
• Comprised of upper motor neurons (UMN) and lower motor neurons (LMN)
  • UMN start in the cortex
  • LMN are in the spinal cord's anterior grey horn

Descending Pathway

• UMN Pathway: Cortex ➔ Brainstem ➔ Spinal Cord
• Synapses occur in the spinal cord
• Other cortical tracts: Corticonuclear fibers (cortex to cranial nerve nuclei)

Cortex Anatomy

• Precentral Gyrus: Primary motor cortex
• Premotor Cortex: Learned, repetitive/planned movements
• Supplemental Motor Area: Certain motor movements
• Primary Somatosensory Cortex: 30-40% of motor fibers

Role and Functions

Motor Control

• Primary Motor Cortex: Voluntary muscle movement
• Premotor & Supplemental Areas: Planning and executing movements

Coordination

• Basal Nuclei and Cerebellum: Check and balance system for movement execution
  • Prevent overshooting/undershooting in movements

Pathway and Decussation

• Cerebral Peduncles ➔ Pons ➔ Medulla
• Pyramidal Decussation: 80% of fibers cross in the pyramids
  • Lateral corticospinal tract: Crossed fibers
  • Anterior corticospinal tract: Some stay uncrossed

Motor Neurons and Muscle Innervation

Types of Neurons

• Alpha Motor Neurons: Innervate extrafusal muscle fibers
• Gamma Motor Neurons: Innervate intrafusal fibers (muscle spindles)

Muscle Activation

• Alpha and Gamma Co-activation: Facilitates muscle contraction and tone

Specific Functions

• Lateral Corticospinal Tract: Distal musculature, fine precise movements
• Anterior Corticospinal Tract: Axial musculature, gross movements

Summary

• Understanding the corticospinal tracts helps in comprehending how voluntary movements are controlled from the brain to the skeletal muscles.
• The integration of various brain regions ensures smooth and coordinated motor functions.