Corpus: Medulla oblongata

The medulla oblongata, or MO for short, is the most caudal part of the brain, located between the pons (bridge) and the spinal cord. Together with the pons and the cerebellum, it forms the rhombencephalon and is a control centre for many vital functions and reflexes.

The medulla oblongata develops from the myelencephalon.

The cranial boundary of the medulla oblongata forms the bridge (pons). Caudally, the medulla oblongata merges into the spinal cord without a sharp boundary. By definition, its end is marked by the exit of the first spinal nerve.

3.1. Classification

The medulla oblongata can be divided functionally into 3 sections, from ventromedial to dorsal:

• Pyramides: pyramidal tract
• Olive: Nucleus olivaris inferior
• Tegmentum myelencephali

The myelencephalic tegmentum contains numerous important nuclear areas:

• Formatio reticularis (esp. cranial medulla oblongata)
• Nuclear areas of cranial nerves:
  • Nucleus spinalis nervi trigemini: V
  • Nucleus tractus solitarii: VII, IX, X
  • Cochlear nucleus: VIII
  • Nucleus ambiguus: IX, X, XI
  • Nucleus dorsalis nervi vagi: X
  • Nucleus nervi accessorii: XI
  • Nucleus nervi hypoglossi: XII
• Posterior cord nuclei (especially caudal medulla oblongata):
  • Nucleus cuneatus
  • Nucleus gracilis

3.2. Marking structures

Macroscopically, the following structures are particularly impressive:

• Ventrally lie the pyramids, which are formed by the nerve fibres of the pyramidal tracts. The pyramidal tract junction (decussatio pyramidum) is recognisable underneath. Lateral to the pyramids are the olives. They contain several core areas, the olive nuclei, which are important for the coordination of fine motor skills.
• On the ventral outer surface, a depression can be recognised in the median plane, the fissura mediana anterior medullae oblongatae.
• The hypoglossal nerve (XII cranial nerve) emerges between the pyramids and the olives.
• Dorsally, the posterior cords of the spinal cord end in the tuberculum gracile and the tuberculum cuneatum. These contain the posterior cord nuclei nucleus gracilis and nucleus cuneatus, in which the nerve fibres of the epicritical sensibility end.

3.3. Blood supply

The medulla oblongata is essentially supplied by the following arteries:

• Anterior spinal artery: supplies the anteromedial parts of the medulla oblongata
• Arteria cerebelli posterior inferior ("PICA"): Branch of the vertebral artery that supplies the posterolateral portion of the MO, where the afferent pathways predominantly run.
• Direct branches of the vertebral artery: are responsible for the blood supply to the MO parts that lie between the supply areas of the other two arteries.

The vascular supply of the medulla oblongata is subject to major inter-individual differences. For this reason, other vessels can also contribute to the supply of the MO, e.g. the anterior inferior cerebellar artery ("AICA").

The medulla oblongata contains important neuronal centres for the control of blood circulation and respiration, as well as reflex centres for the sneezing, coughing, swallowing and sucking reflexes. The vomiting centre is also located here. In addition, the medulla oblongata harbours receptors that are important for the regulation of the acid-base balance.

Damage to the medulla oblongata, e.g. due to trauma (see lower incarceration), is acutely life-threatening due to the threat to vital centres. The resulting clinical picture is known as bulbar brain syndrome.

Complete failure of the medulla oblongata usually leads to death.