Lecture Notes: Spinal Cord Pathways and Neural Tracts

Review of Ascending Pathways

• Posterior Funiculus

  • Sensory modality: Kinesthetic sense (Proprioception)
  • Pathway:
    • Dorsal Root Ganglia (DRG): First neuron
    • Medulla: Second neuron
    • Thalamus: Third neuron, all ascending paths reach the thalamus before moving to the cortex
  • Fasciculus Cuneatus and Gracilis: Major tracts in posterior funiculus

• Lateral Spinothalamic Tract

  • Carries pain and temperature sensations
  • Pathway:
    • DRG: First neuron
    • Dorsal horn (Substantia gelatinosa): Second neuron
    • Thalamus: Third neuron

• Sensory Cortex

  • Located at the postcentral gyrus

Descending Pathways

• Corticobulbar Tract

  • Origin: Cerebral cortex
  • Terminates at cranial nerve nuclei in the brainstem
  • Example: Fifth cranial nerve nucleus for muscles of mastication

• Corticospinal Tract

  • Origin: Precentral gyrus (motor cortex)
  • Pathway:
    • Descends through the internal capsule, midbrain (cerebral peduncles), and medulla (pyramids)
    • Decussation of Pyramids: Crossing of fibers in the medulla
    • Lateral corticospinal tract (crossed): Descends in lateral funiculus
    • Anterior corticospinal tract (uncrossed): Descends in anterior funiculus and crosses at the segmental level in the spinal cord
  • Function: Controls voluntary motor activity

Upper and Lower Motor Neurons

• Upper Motor Neurons (UMN)

  • Located in cortex
  • Lesion symptoms:
    • Flaccid paralysis
    • Loss of superficial reflexes
    • Exaggeration of deep tendon reflexes
    • Positive Babinski sign

• Lower Motor Neurons (LMN)

  • Located in anterior horn of spinal cord
  • Lesion symptoms:
    • Loss of reflexes
    • Muscle atrophy
    • Paralysis
  • Example disease: Polio

Cerebral Hemispheres

• Cerebral Cortex

  • Thin outer layer of the brain
  • Frontal lobe largest, contains motor areas

• Broadmann's Areas

  • Area 4: Precentral gyrus, refined motor (corticospinal tract origin)
  • Area 6: Pre-motor and supplementary motor areas (motor planning)
  • Area 8: Frontal eye fields for conjugate eye movements

• Motor and Sensory Homunculus

  • Maps of sensory and motor areas in the cortex

• Basal Ganglia

  • Modify motor behavior, keeping movements smooth and coordinated

Important Neuroanatomy

• Internal Capsule

  • Pathway for descending fibers
  • Damage can lead to paralysis

• Corona Radiata

  • White matter tract connecting cortex to brainstem

• Brainstem Regions

  • Midbrain: Cerebral peduncles contain motor pathways
  • Upper Medulla: Contains pyramids
  • Lower Medulla: Site of pyramidal decussation

These notes summarize the structure and function of major pathways in the spinal cord and brain, emphasizing the importance of these tracts in sensory and motor functions and their clinical implications.