Substantia Reticularis

SUBSTANTIA RETICULARIS, s. formatio reticularis, syn. network-like formation, complex association apparatus, located in the brainstem. S. r. is formed by fibers running in all directions, between which cellular elements are located. The following are distinguished: 1) substantia reticularis alba, when the number of nerve fibers predominates over cellular elements, and 2) substantia reticularis grisea, when there are more cellular elements; both of these formations are closely connected and one passes into the other. The continuation of S. r. into the spinal cord is known under the name processus reticularis; it is located in the inner part of the lateral column between the posterior and anterior horns. In the medulla oblongata, S. r. occupies almost entirely the lateral columns, in which the anterior and posterior horns of the spinal cord dissolve. Nerve cells lie separately and in groups. A group of cells, fairly large in size, located in the anterior parts of S. r., is distinguished under the name anterior nucleus of the lateral column (nucl. funiculi lateralis). In the higher parts of the medulla oblongata, the appearing olives displace S. r. somewhat backward; in addition to the anterior nucleus, the middle nucleus of the lateral column (Roller's) or nucl. ambiguus and the posterior nucleus, located at the anterior edge of the spinal root of n. trigemini, formed by round or oval pigmented cells, appear. Between nucl. ambiguus and the olive lies nucl. salivatorius inferior, fibers from which through n. IX go to glandula parotis. S. r. of the lateral columns is richer in cellular elements and can be attributed to S. r. grisea, while S. r. located in the anterior area, behind the pyramids, has relatively few cells and can be attributed to S. r. alba. The nucleus of the anterior column lies behind the accessory internal olive. In the Varolian pons, S. r. is located in its tegmentum between lem-niscus medialis, oliva superior, located anteriorly, and the central gray matter of the IV ventricle posteriorly. Instead of nucl. ambiguus lies the nucleus of n. VII, fibers of which have a winding course in S. r. until their exit from the pons. Behind the nucleus of n. VII scattered cells are located, collectively forming the nucleus-nucl. salivatorius sup. In the middle parts of the Varolian pons, due to the disappearance of nuclei nn. VI and VII, S. r. increases in size. In its anterior-inner part on both sides of raphe is located the reticular nucleus of the tegmentum, s. nucl. reticularis tegmenti, s. nucl. magno-cellularis diffusus Kolliker's, s. nucl. oculo-pontinus Kohnstamm's. In S. r. pass the central pathways nn. V, IX and X, the central tegmental bundle, the bundle of Monak.--In its higher parts, in addition to the formations described above, a small-celled nucleus appears along the median line-the superior central nucleus; outward and forward from the posterior longitudinal bundle lies nucl. tegmenti ventralis Gudden's; in the lateral parts of S. r. between lemniscus medialis and brachium conjunctivum lies a layer of gray matter-lateral nucleus of the tegmentum (Kolliker's).-In the cerebral peduncle S. r. is also located in the tegmentum, behind and inside lemniscus, in front of the central substance of aq. Sylvii and outside the decussation of brachii conjunctivi and nucl. rubri. In its posterior-inner part pass longitudinal bundles-fasc. tegmenti Forel's. In S. r. there are fibers of different lengths, thanks to which connections are established between certain nuclei located either in S. r. itself or outside it. S. r. is connected with the spinal cord via fibrae reticulo-spinales laterales et ventrales; fibrae reticulo-spinales lat. on their path form a decussation; they go in the lateral column of the spinal cord. Fibrae reticulo-spinalis ventr. originate from cells of S. r. mainly, on the other hand, they go mainly in the anterior column bundle of the spinal cord. In addition to the spinal cord, S. r. is connected with the cerebellum via the hook-shaped bundle, which, originating from the tegmental nucleus of the cerebellum, partially ends in S. r. Nucleus ruber is connected with S. r. via fasc. rubro-reticularis, which originates from the middle and inner parts of the main small-celled part of nucl. rubri. With the anterior quadrigeminal body S. r. is connected via fibrae tecto-reticulares, i. tractus tecto-pontinus, or the bundle of Münzer's. From thalamus opticus fibers go to S. r. of the Varolian pons-fibrae thalamo-reticulares; their connection is decussating, occurs with the help of the posterior commissure of the brain. The continuation of all these systems further down-into the spinal cord-serves fibrae reticulo-spinales. Through S. r. pass autonomic pathways from the diencephalon to spinal sympathetic centers; vaso-motor pathways, sweat-secretory are located in the lateral parts of S. r.; at the level of the medulla oblongata they decussate. Along these pathways in the medulla oblongata are located cellular groups. In the posterior-inner part passes the ocular sympathetic pathway, which decussates above the Varolian pons. According to Edinger's expression, S. r. is the "association field of the medulla oblongata"; this concept can be somewhat expanded and say "association field of the brainstem". With the help of S. r. various combinations of muscle centers occur. In the medulla oblongata, where the centripetal fibers of the vagus nerves end and where are located the motor centers of the larynx, bronchi, soft palate, etc., S. r. coordinates the respiratory centers; with the dorsal centers of respiratory muscles S. r. is connected via fibrae reticulo-spinales. With short ascending fibers S. r. of the medulla oblongata is connected with the nucleus of n. facialis, thanks to which the facial muscles participate in intensified breathing. In S. r. various sensory fibers from the roots of nn. X, IX, V, from the bundle of Gowers branch out; with the help of these fibers various respiratory reflexes from mucous membranes and from the skin can be caused. Such coordination of muscle centers occurs in S. r. also for other complex acts, as swallowing, chewing, etc. The syndrome of disease of S. r. has not been distinguished, it is masked by the simultaneous disease of the formations located in it. In experiments it has been shown that destruction of this area gives prolonged cessation of breathing on the corresponding side; while irritation of S. r., on the contrary, accelerates breathing (see figure Medulla oblongata, fig. 5 and Varolian pons, fig. 3 and 4).