Human Anatomy
Medulla Oblongata
Medulla oblongata anatomy for MBBS: pyramids, olives, decussations, cranial nerve nuclei and medial and lateral medullary syndromes, mapped to NMC codes AN58.1 to AN58.4.
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Medulla Oblongata
Medulla oblongata anatomy for MBBS: pyramids, olives, decussations, cranial nerve nuclei and medial and lateral medullary syndromes, mapped to NMC codes AN58.1 to AN58.4.
This chapter describes the surface features, internal transverse anatomy and cranial nerve nuclei of the medulla oblongata. It explains the classic medial and lateral medullary syndromes that follow occlusion of the vertebral and cerebellar arteries.
High-yield: Medulla Oblongata
- The medulla oblongata is the lowest part of the brainstem, continuous below with the spinal cord and above with the pons.
- The pyramids on its anterior surface contain the corticospinal fibres, most of which cross in the pyramidal decussation.
- The olive, lateral to the pyramid, overlies the inferior olivary nucleus, which relays to the cerebellum.
- The hypoglossal nerve emerges from the antero-lateral sulcus between the pyramid and the olive.
- The glossopharyngeal, vagus and cranial accessory nerves emerge from the postero-lateral sulcus behind the olive.
- The lower part of the fourth ventricle lies behind the open part of the medulla.
- At the level of the pyramidal decussation, crossing corticospinal fibres interrupt the anterior median fissure.
- At the level of the sensory decussation, the internal arcuate fibres cross to form the medial lemniscus.
- The nucleus gracilis and nucleus cuneatus receive the dorsal columns and give rise to the internal arcuate fibres.
- The medial medullary syndrome, from anterior spinal or vertebral artery occlusion, gives contralateral hemiplegia, contralateral dorsal column loss and ipsilateral tongue palsy.
- The lateral medullary or Wallenberg syndrome, from posterior inferior cerebellar artery occlusion, gives ipsilateral facial and contralateral body pain and temperature loss.
- Wallenberg syndrome also causes ipsilateral Horner's syndrome, dysphagia, hoarseness and cerebellar ataxia.
- The nucleus ambiguus supplies motor fibres to the ninth, tenth and cranial eleventh nerves for the pharynx and larynx.
- The dorsal nucleus of the vagus provides parasympathetic supply to thoracic and abdominal viscera.
- The medulla houses the vital cardiac, respiratory and vasomotor centres of the reticular formation.
Medullary syndromes compared
- **Medial medullary syndrome:** Anterior spinal artery. Contralateral hemiplegia, contralateral dorsal column loss, ipsilateral tongue deviation from hypoglossal palsy.
- **Lateral medullary (Wallenberg):** Posterior inferior cerebellar artery. Ipsilateral face and contralateral body pain and temperature loss, Horner's, dysphagia, ataxia.
- **Pyramidal decussation level:** Corticospinal fibres cross; interrupts the anterior median fissure.
- **Sensory decussation level:** Internal arcuate fibres cross to form the medial lemniscus.
NMC competencies in this chapter
- **AN58.1:** External features of the medulla oblongata
- **AN58.2:** Transverse section at the levels of pyramidal decussation, sensory decussation and the inferior olivary nucleus
- **AN58.3:** Cranial nerve nuclei of the medulla and their functional groups
- **AN58.4:** Anatomical basis and effects of medial and lateral medullary syndromes
Frequently Asked Questions
What arteries cause the two medullary syndromes?
The medial medullary syndrome follows occlusion of the anterior spinal artery or vertebral artery, and the lateral medullary or Wallenberg syndrome follows occlusion of the posterior inferior cerebellar artery.
Why does the tongue deviate in medial medullary syndrome?
The hypoglossal nucleus or its emerging fibres are damaged, so the ipsilateral half of the tongue is weak and the tongue points towards the lesioned side on protrusion.
What sensory pattern defines Wallenberg syndrome?
There is loss of pain and temperature on the same side of the face, from the spinal trigeminal tract, and on the opposite side of the body, from the spinothalamic tract, a crossed sensory finding.
Which structures cross at the sensory decussation?
The internal arcuate fibres arising from the nucleus gracilis and nucleus cuneatus cross the midline to form the contralateral medial lemniscus, carrying fine touch and proprioception upward.
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