Thursday, February 26, 2015
The Medulla Oblongata
The most prominent anterior features of the medulla oblongata are the medullary pyramids. They appear on the anterior surface as two vertically running rounded eminences which emerge from under the pons to become continuous with the spinal cord below. In the lowest portion of the anterior medulla, descending corticospinal (pyramidal) tract fibers cross over in the pyramidal decussation. The corticospinal tracts are often called pyramidal tracts because of the unique pyramidal shape they give to the anterior medulla as they descend into the spinal cord. The olive is a lateral feature of the medulla. Emerging from the lateral medulla posterior to the olive in descending order are the glossopharyngeal nerves (IX), the vagus nerves (X), and the bulbar accessory nerves (XI). The hypoglossal nerves (XII) emerge from the lateral medulla anterior to the olive.
Three sulci are visible in posterior view, a single posterior median sulcus and two laterally placed posterior intermediate sulci. Two rounded eminences, the gracile tubercle (clava) and the cuneate tubercle are observed on either side of the posterior median sulcus. The fasciculus gracilis leads to the former while the fasciculus cuneatus leads to the latter. The posterior intermediate sulcus separates the fasciculus gracilis and gracile tubercle from the fasciculus cuneatus and cuneate tubercle on either side.
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