Medulla

The oblong brain (medulla oblongata, s. Myelencephalon) is located between the hindbrain and the spinal cord. The upper border of the medulla oblongata on the ventral surface of the brain passes along the lower edge of the bridge. On the dorsal surface, this boundary corresponds to the cerebral stria of the IV ventricle, which divide the bottom of the IV ventricle into the upper and lower parts. The boundary between the oblong and spinal cord corresponds to the level of the large occipital opening or to the point of exit from the brain of the upper part of the roots of the first pair of spinal nerves.

The upper divisions of the medulla oblongata are somewhat thicker than the lower ones. In this regard, the medulla oblongata takes the form of a truncated cone or bulb, for which similarity it is also called a bulbus bulbus. The length of the medulla oblongata is 25 mm.

In the medulla oblongata, the ventral, dorsal and two lateral surfaces are distinguished, which are divided by furrows. The furrows of the medulla oblongata are a continuation of the fissures of the spinal cord and bear the same names. This is the anterior median fissure (fissura mediana ventralis, s. Anterior); posterior median furrow (sulcus medianus dorsalis, S. Posterior); anterolateral groove (sulcus ventrolateralis, s. Anterolateralis); posterolateral groove (sulcus dorsolateralis, s., posterolateral). On either side of the anterior median slit there are convex, gradually narrowing downward pyramides on the ventral surface of the medulla oblongata. In the lower part of the medulla oblongata, the bundles of fibers that make up the pyramids pass to the opposite side and enter the lateral cord of the spinal cord. This transition of fibers was called the cross of the pyramids (decussatio pyramidum, s. Decussatio motoria; motor cross). The intersection site also serves as an anatomical boundary between the oblong and spinal cord. On the side of each pyramid of the medulla oblongata there is an oval elevation - oliva (oliva), which is separated from the pyramid by an anterolateral furrow. In this groove, the roots of the hyoid nerve (XII pair) come out of the medulla oblongata.

On the dorsal surface, at the sides of the posterior median sulcus, thin and wedge-shaped fascicles of the posterior cords of the spinal cord terminate in thickening, separated from each other by a posterior intermediate groove. Lying more medially thin fasciculus (fasciculus gracilis), expanding, forms a tubercle of a thin nucleus (tuberculum gracile). A wedge-shaped fasciculus (fasciculus cuneatus), lateral to the tubercle of the thin bundle, forms the tubercle of the wedge-shaped nucleus (tuberculum cuneatum) laterally. Dorsal to the olive from the posterolateral groove of the medulla oblongata - pozadiolivnoy furrow (sulcus retroolivaris) leaves the roots of the lingo-pharyngeal, vagus and additional nerves (IX, X and XI pairs).

The dorsal part of the lateral cord is somewhat widened to the top. Here, fibers are attached to it, departing from the wedge-shaped and fine nuclei. All together they form the lower cerebellar pedicel, also called the rope body. The surface of the medulla oblongata, bounded from below and laterally by the lower cerebellar pedicles, participates in the formation of a rhomboid fossa, which is the bottom of the IV ventricle.

Clusters of white and gray matter are visible on the cross section, drawn through the medulla oblongata at the level of the olive. In the lower lateral divisions there are the right and left lower olive nuclei (nuclei olivares caudales [inferiores]). They are curved in such a way that their gates are turned medially and upwards. Somewhat higher than the lower olive nuclei is the reticular formation (formatio reticularis), formed by the intertwining of nerve fibers and the nerve cells lying between them and their clusters in the form of small nuclei. Between the lower olive nuclei is located the so-called interlayer layer, represented by internal arc-shaped fibers (fibrae arcuatae internae) - the outgrowths of cells lying in the thin and wedge-shaped nuclei. These fibers form a medial loop (lemniscus medialis). The fibers of the medial loop belong to the proprioceptive path of the cortical direction and form in the medulla oblong the cross of medial loops (decussatio lemniscorum medianum). In the upper-lateral sections of the medulla oblongata, the right and left lower cerebellar legs are visible on the cut. Several fibers of the anterior spinal-cerebellar and red-nuclear-spinal cord pass somewhat ventrally. In the central part of the medulla oblongata, along the sides of the anterior median slit, there are pyramids. Above the crosshairs of the medial loops is the medial longitudinal fasciculus (fasciculus longitudinalis medialis [posterior]).

In the medulla oblongata lie the nuclei IX, X, XI and XII pairs of cranial nerves that take part in the innervation of internal organs and derivatives of the gill apparatus. Here, ascending conduction paths to other parts of the brain pass. The ventral divisions of the medulla oblongata are represented by descending motor pyramidal fibers. Dorsolaterally through the medulla oblongata there are ascending conducting paths connecting the spinal cord with the cerebral hemispheres, the brain stem and the cerebellum. In the medulla oblongata, as in some other parts of the brain, there is a reticular formation, as well as such vital centers as the centers of circulation, respiration and digestion.

[1], [2], [3], [4], [5], [6], [7], [8]