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Overview
                
 
Introduction
  • The brainstem is composed of the midbrain, pons, and medulla
Brainstem Structures
Structure Cranial Nerves Comments

Midbrain (Mesencephalon)

  • Oculomotor nerve (CN III)
  • Trochlear nerve (CN IV)
  • Reticular activating system
    • involved in arousal and alertness
    • lesion can lead to coma
  • Superior colliculus
    • conjugate vertical gaze center
  • Inferior colliculus
    • auditory information processor
  • Parinaud's syndrome
    • due to compression of dorsal midbrain and pretectal area (e.g., pinealoma, hydrocephalus) 
      • lesions the superior colliculus
    • conjugate vertical gaze palsy

Pons (Metencephalon)

  • Trigeminal nerve (CN V)
  • Abducens nerve (CN VI)
  • Facial nerve (CN VII)
  • Vestibulocochlear nerve (CN VIII)
  • Medial longitudinal fasciculus
    • lesion leads to intranuclear ophthalmoplegia (INO)

Medulla (Myelencephalon)

  • Glossopharyngeal nerve (CN IX)
  • Vagus nerve (CN X)
  • Hypoglossal nerve (CN XII)
  • Vasomotor center
  • Respiratory center
  • Area postrema
    • incomplete blood-brain barrier
    • chemoreception of toxins
      • triggers nausea and vomiting
  • Medial lemniscus
    • formed by decussating fibers of the nucleus gracillis and cuneatus
  • Pyramids
    • contain corticospinal tracts
      • most decussate in the caudal medulla
  • Olives
    • send fibers through the inferior cerebellar peduncle
    • distinguishing feature of medulla
 

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