Human Anatomy - Kotsan I. Y. 2009

Brain
Medulla Oblongata

The Medulla Oblongata (myelencephalon) is one of the most phylogenetically ancient structures of the vertebrate Brain. It serves as a direct continuation of the Spinal Cord. The lower boundary of the medulla is conventionally defined by the exit of the roots of the first pair of Spinal Nerves or the pyramidal decussation, while the upper boundary is marked by the lower border of the Pons. The upper portion of the medulla is somewhat broader than the lower part, giving it the shape of a truncated cone or a bulb—hence its alternative designation as the spinal bulb. In adult humans, the length of the medulla oblongata averages 25 mm.

The medulla oblongata presents four surfaces: ventral (anterior), dorsal (posterior), and two lateral surfaces, which are demarcated by sulci. These sulci are direct continuations of the spinal cord grooves and share their nomenclature: the anterior median fissure (fissura mediana anterior), posterior median sulcus (sulcus medianus posterior), anterolateral sulcus (sulcus anterolateralis), and posterolateral sulcus (sulcus posterolateralis).

On the ventral surface of the medulla, situated on either side of the anterior median fissure, are the pyramids (pyramides)—prominent longitudinal elevations that taper inferiorly. In the lower region of the medulla, the fiber bundles comprising the pyramids cross the midline to enter the lateral funiculi of the spinal cord, a phenomenon known as the pyramidal decussation (decussatio pyramidum). Absent in lower vertebrates, the pyramids emerge in parallel with the Evolution of the neocortex; consequently, they are most highly developed in humans, where pyramidal fibers connect the Cerebral Cortex—having achieved its maximal development in humans—with the cranial nerve nuclei and the anterior horns of the spinal cord.

Lateral to the pyramid of the medulla oblongata lies an oval elevation known as the olive (oliva), which is separated from the pyramid by the anterolateral sulcus.

On the posterior (dorsal) surface of the medulla, flanking the posterior median sulcus, lie the posterior funiculi, bounded laterally by the subtle posterolateral sulcus. Superiorly, the posterior funiculi diverge and extend toward the Cerebellum to form its inferior cerebellar peduncles. Each posterior funiculus is divided by an intermediate sulcus into a medial fasciculus gracilis and a lateral fasciculus cuneatus. Near the inferior apex of the Rhomboid fossa, the gracile and cuneate fasciculi terminate in corresponding tubercles, which contain The Nucleus gracilis and nucleus cuneatus.

The lateral surface of the medulla oblongata, located between the anterolateral and posterolateral sulci, corresponds to the lateral funiculus. Emerging from the posterolateral sulcus, dorsal to the olive, are the rootlets of the glossopharyngeal, vagus, and accessory Cranial Nerves (IX, X, and XI pairs).