Medulla Oblongata

What is the location and extent of medulla oblongata.

Medulla oblongata is the lowermost part of the brainstem (other parts are pons and midbrain). It is:

• continuous below with the spinal cord and above with pons.
• located in the  posterior cranial fossa  and is  related to clivus anteriorly and cerebellum posteriorly.
• separated from the cerebellum by the cavity of fourth ventricle.

 Describe the external features of medulla oblongata.

 Medulla oblongata is

• pyriform shaped, broad  in the upper part and narrow in the lower part.
• approximately 3 cm in length.
• divided into two part:
  • Lower closed part:  It has a central canal.
  • Upper open part : In this part the central canal widens and opens dorsally to form the lower half of the floor of fourth ventricle.

Ventral Aspect of Medulla Oblongata

The ventral aspect of medulla oblongata shows the following features from medial to lateral:

• Anterior median fissure/sulcus in the median plane (divides ventral aspect into two symmetrical halves).
• Pyramids: Elongated elevation produced by underlying corticospinal tract.
• Anterolateral sulcus: Hypoglossal nerve rootlets emerge along this sulcus.
• Olive: Oval elevation produced by underlying Inferior olivary nucleus.
• Posterolateral sulcus: Rootlets of glossopharyngeal, vagus and cranial part of accessory nerves emerge along this sulcus from above downward.

Dorsal Aspect of Medulla Oblongata

Features of the dorsal surface of lower closed part of medulla oblongata from medial to lateral are:

• Posterior median sulcus: In the median plane.
• Fasciculus gracilis (lowerpart) and gracile tubercle (in the upper part): gracile tubercle is produces by the underlying nucleus gracilis, where the axons comprising fasciculus gracilis terminate.
• Fasciculus cuneatus (lowerpart) and cuneate tubercle (in the upper part): cuneate tubercle is produces by the underlying nucleus cuneatus, where the axons comprising fasciculus cuneatus terminate.
• Inferior cerebellar peduncle:  Connects medulla to cerebellum.

Dorsal surface of upper open part of medulla oblongata

Dorsal surface of upper part of medulla forms the lower half of the floor of fourth ventricle. The transversely running stria medullaris fibers separate the dorsal surface of medulla from that of pons. These fibers originate from arcuate nucleus ( dislodged pontine nuclei) and reach the cerebellum  via inferior cerebellar peduncle. Features of the dorsal surface of upper open part of medulla oblongata from medial to lateral are:

• Median sulcus: in the median plane.
• Medial eminence: shows two triangular areas, hypoglossal triangle above and vagal triangle below, which overlie the nucleus of  hypoglossal nerve and dorsal motor nucleus of vagus respectively. Below the vagal triangle lies area postrema ( chemoreceptor trigger zone (CTZ) which trigger vomiting in response to  presence of emetic substances in the blood). Area postrema is devoid of blood brain barrier.
• Sulcus limitans: separates medial eminence from vestibular area.
• Vestibular area: inferior and medial verstibular nuclei lie deep to this area.

Describe the internal structure of medulla oblongata.

Structural components forming grey and white matter of medulla oblongata are 

Transverse sections of the medulla oblongata at the level of pyramidal decussation.

Transverse sections of the medulla oblongata at the level of sensory decussation

Transverse sections of the medulla oblongata at the level of olive (open part of medulla)

Describe the arterial supply of medulla oblongata.

The medulla oblongata is supplied by  the following arteries:

• Vertebral arteries.
• Anterior and posterior spinal arteries.
• Anterior and posterior inferior cerebellar arteries.
• Basilar artery.

Applied Aspects