Medulla oblongata (internal anatomy)

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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. 

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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