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Medulla oblongata (internal anatomy)

Learning objectives 

Completion of this study unit will allow you to: 

  1. Develop an understanding of the main divisions and landmarks of the medulla oblongata. 
  2. Identify the main features and functions of the medulla oblongata. 
  3. Name and describe the main nuclei and tracts of the medulla oblongata.

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The medulla oblongata, also known as the myelencephalon, is the caudal-most portion of the brainstem. The rostral medulla continues as the pons, forming the pontomedullary junction with it. Caudally, the medulla oblongata continues as the spinal cord after passing through the foramen magnum. Much like the rest of the brainstem, the medulla oblongata is made up of ascending and descending white matter tracts and brainstem nuclei.

The medulla oblongata is typically divided into two main regions: superior (open) and inferior (closed), depending on whether it is surrounded by CSF containing cavities. The inferior or closed medulla starts as the medulla closes around the fourth ventricle, which narrows at the obex to become the central canal. The superior part of the medulla oblongata begins when the central canal expands into the fourth ventricle.

The medulla oblongata can also be divided from ventral to dorsal, forming three laminae: the basis, tegmentum and tectum. The basis contains the pyramids and pyramidal decussation, while the tegmentum houses the olivary nuclei and cranial nerve nuclei of the glossopharyngeal (IX), vagus (X), accessory (XI), and hypoglossal (XII) cranial nerves. The tectum of the medulla is composed of the inferior medullary velum, which is the posteroinferior part of the fourth ventricle.

Nuclei of the medulla oblongata can be generally divided into three groups: the cranial nerve nuclei, the relay nuclei, which relay the stimuli from peripheral receptor areas to higher cortical centers and reticular nuclei which belong to the reticular formation.

The main functions of the medulla oblongata include relaying information from the spinal cord to the brainstem through a number of nuclei and tracts and regulating heart rate, blood pressure, and breathing through the cardiovascular-respiratory regulatory system. 

Explore the nuclei and tracts of the medulla oblongata in the videos below. Take a look at a cross section of the medulla oblongata at the level of the hypoglossal nerve first. 

Now explore a cross section of the medulla oblongata at the level of the vagus nerve. 

Take a quiz

Test your knowledge on the internal structure of the medulla oblongata with the quiz below.

Looking for a broader array of questions on the brainstem? Try out our fully customizable quiz below!

Browse atlas

Take a look at the atlas galleries below to explore the various nuclei and tracts of the medulla oblongata at different levels, beginning with the hypoglossal nerve level.

Summary

Internal structure of medulla oblongata (hypoglossal nerve level)
Nuclei Cranial nerve nuclei: Spinal nucleus of trigeminal nerve, nucleus of solitary tract, nucleus ambiguus, dorsal nucleus of vagus nerve, nucleus of hypoglossal nerve

Relay nuclei
: Gracile nucleus, cuneate nucleus, arcuate nucleus, olivary nuclei (inferior olivary nucleus, posterior accessory olivary nuclei)

Reticular nuclei
: Lateral reticular nucleus
Tracts Motor tract: Pyramidal tract

Sensory tracts
: Spinal tract of trigeminal nerve, olivocerebellar tract, medial lemniscus, superficial arcuate fibers, central tegmental tract, internal arcuate fibers, medial longitudinal fasciculus, solitary tract, spinocerebellar tract, spinothalamic tract
Reticular formation Composed of numerous nuclei (lateral, medial and median nuclei groups) and ascending/descending fibers (projecting fibers)
Internal structure of medulla oblongata (vagus nerve level)
Nuclei Cranial nerve nuclei: Spinal nucleus of trigeminal nerve, nucleus of solitary tract, nucleus ambiguus, dorsal nucleus of vagus nerve, nucleus of hypoglossal nerve, medial vestibular nucleus

Relay nuclei
: Gracile nucleus, cuneate nucleus, olivary nuclei (principal inferior olivary nucleus, posterior accessory olivary nucleus, medial accessory olivary nucleus)

Reticular nuclei
: Raphe nuclei, subhypoglossal nucleus, lateral reticular nucleus
Tracts Motor tract: Pyramidal tract

Sensory tracts
: Spinal tract of trigeminal nerve, medial lemniscus, medial longitudinal fasciculus, inferior cerebellar peduncle, solitary tract, spinocerebellar tract, spinothalamic tract
Reticular formation Composed of numerous nuclei (lateral, medial and median nuclei groups) and ascending/descending fibers (projecting fibers)

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