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Overview of Spinal Cord Pathways

Apr 8, 2025

Descending Motor Pathways in the Spinal Cord

Types of Descending Pathways

  • Divided into:
    • Pyramidal tracts
    • Extrapyramidal tracts

Pyramidal Tracts

  • Travel through: Medullary pyramids of the medulla oblongata
  • Originate from: Cerebral cortex
  • Function: Voluntary control of muscles of the body and face

Components of Pyramidal Tracts

  1. Corticospinal Tracts

    • Control body muscles
    • Pathway:
      • Cell bodies in cerebral cortex
      • Axons pass through internal capsule, crus cerebri in midbrain, pons, medulla oblongata
      • 75% decussate to opposite side (lateral corticospinal tract)
      • 25% remain ipsilateral (anterior corticospinal tract)
      • Synapse with lower motor neurons in ventral horns
  2. Corticobulbar Tracts

    • Control head, face, neck muscles
    • Pathway:
      • Originate from cerebral cortex
      • Axons pass through internal capsule
      • Synapse with cranial nerve nuclei in brainstem
    • Unique Feature: Bilateral innervation (exceptions: lower third of face with cranial nerve VII, hypoglossal nerve)

Extrapyramidal Tracts

  • Do not pass through: Medullary pyramids
  • Function: Involuntary control, modulation of muscles (e.g., muscle tone, balance)
  • Originate from: Brainstem

Components of Extrapyramidal Tracts

  1. Rubrospinal Tract

    • Origin: Red nucleus in midbrain
    • Function: Fine motor control, primarily upper limbs
    • Innervation: Contralateral
  2. Reticulospinal Tracts

    • Medial (Pontine) Reticulospinal Tract
      • Origin: Pontine reticular formation
      • Function: Facilitates voluntary movement, excites extensor muscles, increases muscle tone
    • Lateral (Medullary) Reticulospinal Tract
      • Origin: Medullary reticular formation
      • Function: Inhibits voluntary movement, decreases muscle tone, regulates automatic breathing
  3. Vestibulospinal Tract

    • Origin: Vestibular nuclei
    • Function: Balance, posture
    • Innervation: Ipsilateral
  4. Tectospinal Tract

    • Origin: Superior colliculus in midbrain
    • Function: Coordination of head and eye movements
    • Innervation: Contralateral

Characteristics of Descending Pathways

  • No second neuron in CNS
  • Signal Pathway: Cell body in cerebral cortex or brainstem, travels down spinal cord/brainstem to synapse with lower motor neuron

Lesions in Descending Pathways

Pyramidal Tract Lesions

  • Potential damage sites: Spinal cord, internal capsule
  • Symptoms of Lesions:
    • Hypertonicity (increased muscle tone)
    • Hyperreflexia (exaggerated reflexes)
    • Weakness
    • Clonus (involuntary muscle contractions)
    • Babinski's Sign (upward movement of big toe on stimulation)
    • Hoffmann's Sign (flicking middle finger causes thumb flexion/adduction)

Extrapyramidal Tract Lesions

  • Symptoms:
    • Parkinsonism (rigidity, bradykinesia, tremors, postural deficits)
    • Chorea
    • Athetosis
    • Dystonia