Medulla oblongata

The lowest part of the brainstem, a tapering column between the pons and the spinal cord that holds vital centres for breathing and circulation.

At a glance

English: Medulla oblongata
Latin (TA2): Medulla oblongata
System: Brain and spinal cord
Region: Head
Side: Paired, left and right

About the medulla oblongata

The medulla oblongata, often simply the medulla, is the cone-shaped lower end of the brainstem, about three centimetres long. It runs from the pons down to the level of the foramen magnum, where it becomes the spinal cord just above the first cervical roots. Its old name, the bulb, survives in clinical words such as bulbar palsy, used for weakness of the tongue, throat and larynx muscles it supplies.

It has two levels. In the upper, open part the central canal has widened into the fourth ventricle, whose lower floor forms its back surface. In the lower, closed part the canal is narrow again, and the obex marks the point where the ventricle ends. On the front surface the anterior median fissure runs down the midline, flanked by the pyramids, which carry corticospinal fibres; most of these cross in the pyramidal decussation at the lower end. Lateral to each pyramid lies the oval olive, over the inferior olivary nucleus. On the back surface, below the ventricle, the gracile and cuneate fasciculi end in tubercles over their nuclei, whose fibres cross as internal arcuate fibres to form the medial lemniscus.

Cranial nerves IX to XII leave the medulla in two lines. The hypoglossal rootlets emerge in front of the olive; the glossopharyngeal, vagus and cranial accessory rootlets emerge behind it. Inside lie the nuclei of these nerves, parts of the vestibular and cochlear nuclei, the spinal trigeminal nucleus, the nucleus of the solitary tract and the reticular formation. Networks in the reticular formation set the rhythm of breathing (including the pre-Bötzinger complex), control heart rate and vessel tone through baroreceptor reflexes, and coordinate swallowing, coughing, sneezing, gagging and vomiting.

Because so much is packed into a small space, small lesions give distinctive syndromes. Blockage of a paramedian branch of the vertebral or anterior spinal artery causes the medial medullary syndrome: weakness of the opposite limbs, loss of fine touch and position sense, and paralysis of one side of the tongue. Blockage of the posterior inferior cerebellar or vertebral artery causes the lateral medullary (Wallenberg) syndrome, with vertigo, hoarseness, difficulty swallowing and crossed loss of pain and temperature sense. Downward herniation of the cerebellar tonsils through the foramen magnum compresses the medulla and threatens breathing.

Function and supply

Function: Conducts all ascending and descending tracts between brain and spinal cord; houses the nuclei of cranial nerves IX-XII and the centres that regulate breathing, heart rate, blood pressure, swallowing, coughing and vomiting.
Blood supply: Branches of the vertebral arteries, the anterior spinal artery (medial part), the posterior inferior cerebellar arteries (lateral part) and the posterior spinal arteries (back of the closed part).

Parts of the medulla oblongata

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Anterior median fissure of medulla oblongataFissura mediana anterior medullae oblongataeThe deep midline groove on the front of the medulla, holding a fold of pia, continuous below with the fissure of the spinal cord. It stops at the pons in a small blind pit, the foramen caecum, and is partly hidden low down where the pyramids cross.
Anterolateral sulcus of medulla oblongataSulcus anterolateralis medullae oblongataeThe groove on each side between the pyramid and the olive. Hypoglossal nerve rootlets leave the brainstem along it.
Cuneate tubercleTuberculum cuneatumA rounded swelling on the back of the lower medulla, lateral to the gracile tubercle, made by the cuneate nucleus. That nucleus relays touch and position sense from the upper limb and upper trunk.
Gracile tubercleTuberculum gracileThe swelling next to the midline on the back of the lower medulla, where the gracile fasciculus ends on the gracile nucleus. It relays fine touch and position sense from the lower limb and lower trunk.
Inferior medulla oblongataPars inferior medullae oblongataeThe closed lower part of the medulla, below the obex, which surrounds the narrow central canal much like the spinal cord. It contains the pyramidal decussation and the gracile and cuneate nuclei.
Lateral funiculus of medulla oblongataFuniculus lateralis medullae oblongataeThe column of white matter at the side of the medulla, continuous with the lateral funiculus of the spinal cord. It carries long tracts such as the spinothalamic and spinocerebellar tracts, and lies between the front and back rows of nerve rootlets.
OliveOlivaAn oval bulge on the side of the upper medulla, between the anterolateral and posterolateral sulci. It is produced by the folded inferior olivary nucleus, which sends climbing fibres to the opposite half of the cerebellum.
Posterior median sulcus of medulla oblongataSulcus medianus posterior medullae oblongataeA shallow midline groove on the back of the closed medulla, separating the two gracile fasciculi. It fades upwards and ends at the obex, where the fourth ventricle opens out.
Posterolateral sulcus of medulla oblongataSulcus posterolateralis medullae oblongataeThe groove on each side behind the olive, in line with the spinal dorsal roots. The rootlets of the glossopharyngeal, vagus and cranial accessory nerves are attached along it.
Pyramid of medulla oblongataPyramis medullae oblongataeA long, narrow ridge of white matter on each side of the anterior median fissure. It carries corticospinal and some corticobulbar fibres, most of which cross to the opposite side at its lower end.
Retro-olivary grooveSulcus retroolivarisA narrow groove immediately behind the olive, forming the upper part of the posterolateral sulcus. The glossopharyngeal and vagus nerves emerge from it, with accessory nerve rootlets below.
Superior medulla oblongataPars superior medullae oblongataeThe open upper part of the medulla, whose back surface forms the lower half of the rhomboid fossa, the fourth ventricle's floor. It holds the olives, the hypoglossal and vagal trigones and the area postrema.
Trigeminal tubercleTuberculum trigeminaleA slight longitudinal ridge on the side of the lower medulla, lateral to the cuneate fasciculus, also called the tuberculum cinereum. It overlies the spinal tract and nucleus of the trigeminal nerve, which handle pain and temperature from the face.

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At a glance

About the medulla oblongata

Function and supply

Related structures

See the medulla oblongata where it really sits, with every layer of the body around it.