Medulla Oblongata

Location & General Information

  • Part of brainstem; between upper spinal cord & pons
  • Length ≈ 3 cm3\,\text{cm}
  • Two parts:
    • Lower closed part (central canal present)
    • Upper open part (forms floor of IV ventricle)

External Features

  • Conical shape
  • Anterior median fissure with paired pyramids (corticospinal fibres)
  • Olive lateral to each pyramid (covers inferior olivary nucleus)
  • Posterior midline: fasciculus gracilis → gracile tubercle
  • Lateral to that: fasciculus cuneatus → cuneate tubercle
  • Posterolateral surface forms inferior cerebellar peduncle

Cranial Nerve Attachments

  • Hypoglossal (XII): groove between pyramid & olive
  • Glossopharyngeal (IX), Vagus (X), Accessory-cranial (XI): lateral to olive
  • Abducens (VI): junction of pyramid & pons
  • Facial (VII): junction of olive & pons
  • Vestibulocochlear (VIII): between pons & inferior cerebellar peduncle

Decussations

  • Pyramidal decussation (lower medulla)
    • 80%80\% corticospinal fibres cross → lateral corticospinal tract
    • 20%20\% remain ipsilateral → anterior corticospinal tract (cross lower)
  • Sensory decussation (upper closed medulla)
    • Internal arcuate fibres from nuclei gracilis & cuneatus cross → medial lemniscus

Key Internal Nuclei & Tracts

  • Nucleus gracilis & cuneatus: proprioception & fine touch; give rise to medial lemniscus
  • Hypoglossal nucleus (XII): motor to tongue
  • Dorsal motor nucleus of Vagus (X): parasympathetic to thoracic/abdominal organs
  • Nucleus tractus solitarius: taste (VII, IX, X)
  • Spinal nucleus & tract of Trigeminal (V): pain & temperature from head
  • Nucleus ambiguus (IX, X, XI): motor to palate, pharynx, larynx
  • Inferior olivary nucleus: relay to contralateral cerebellum
  • Vestibular nuclei: balance information (pontomedullary junction)

Vascular Supply & Clinical Syndromes

  • Medial territory: anterior spinal artery (ASA)
  • Lateral territory: posterior inferior cerebellar artery (PICA)

Medial medullary syndrome (ASA thrombosis)

  • Pyramidal tract → contralateral hemiplegia
  • Medial lemniscus → contralateral loss of position, movement, tactile discrimination
  • Hypoglossal fibres → ipsilateral tongue wasting/deviation

Lateral medullary (Wallenberg) syndrome (PICA thrombosis)

  • Nucleus ambiguus → dysphagia, hoarse voice
  • Spinal tract & nucleus of V → ipsilateral facial pain/temperature loss
  • Vestibular nuclei → vertigo, vomiting, nystagmus
  • Inferior cerebellar peduncle → ipsilateral limb ataxia
  • Spinothalamic tract → contralateral limb & trunk pain/temperature loss