Nucleus Ruber

NUCLEUS RUBER, red nucleus, a collection of a large number of ganglion cells having a round shape, slightly elongated in the caudal-oral direction. It is located in the tectum of the midbrain and in the subthalamic area; it is bounded below by the substantia nigra; above it is in the vicinity of the oculomotor nuclei, the fasciculus longitudinalis posterior, and the reticular formation of the tectum, which surrounds it also on the outside except for its lower part, where it contacts the ansa. Caudally, the nucleus ruber is limited by the compact fibers of the brachia conjunctiva, orally

it enters the subthalamic area, where it comes into contact with the fasciculi of Forel (fasciculus lenticularis and fasciculus thalamicus) and with the ansa lenticularis, and laterally borders the corpus Luysi and its capsule, ending at the level of the caudal end of the corpora mammillaria. At the boundary of the posterior ^a/₃ and anterior nuclei of the N. g., the fasciculus retroflexus Meynert passes through it from above downwards and backwards (from the ganglion habenulae to the posterior part of the substantia perforatae posterioris). In the internal part of the N. g., curved fibers of the oculomotor nerve, convex outward, pass. The red nucleus is surrounded on all sides by a capsule of myelinated fibers, which is especially well expressed on its lateral surface, increases in the oral direction, and passes with the termination of the N. g. into a compact mass of fibers, which later divides into the fields H and H₂ of Forel. Histologically, the N. g. consists of several divisions characterized by a different type of ganglion elements. In reptiles and birds it is only outlined as diffusely distributed large cells (Kappers), belonging exclusively to the midbrain. Large cells also predominate in lower mammals - in monotremes, marsupials, rodents, and ungulates. In higher mammals, in carnivores, and in primates the N. r. increases and spreads into the region of the diencephalon at the expense of the formation of an orally located small-cellular part, the development of which proceeds pari passu with the development of the frontal lobe and the cerebellar hemispheres. In man, the small-cellular division of the nuclei rubri is very large, while the phylogenetically old large-cellular division, consisting of cells of a pronounced motor type and having predominant significance in lower mammals, is reduced in him to a rudiment (Monakov), which corresponds also to the very great reduction in man of the descending paths of this nucleus - fasciculi rubro-spinalis. - In preparations treated by Nissl, three types of ganglion elements are found in the nucleus ruber: 1) large polygonal elements resembling motor cells of the anterior horns of the spinal cord, occurring in the caudal part of the nucleus and giving rise to the fasciculus rubro-spinalis (resp. Monakov's bundle); 2) elements of medium size, triangular or rounded shape, with a large nucleus and well-expressed tigroid, distributed throughout the red nucleus, especially in its oral part; finally 3) small spindle-shaped or triangular cells with a short rapidly branching axon, not leaving the limits of the nuclei rubri. The red nucleus possesses numerous connections: it is connected with the cerebellum, with the spinal cord, with the thalamus, with the pallidum, and with the cerebral cortex. Of the afferent paths, the most important is the cerebellar-rubral path (segmento-rubralis), which proceeds in the composition of the superior cerebellar peduncle from the dentate nucleus of the cerebellum, crosses to the other side at the decussation of Forel, and ends in the cells of the N. g. Next, the red nucleus receives afferent conductors from the pallidum through the ansa lenticularis and through the fasciculus lenticularis of Forel. Part of the fibers of the posterior longitudinal bundle end in it, transmitting to it, apparently, impulses from the vestibular apparatus. It is very probable further that the N. g. also receives fibers from the quadrigeminal plate from the cellular accumulations in which the fibers of the optic nerve and the fibers from the nuclei of the auditory nerve end. Finally, the cortico-rubral paths, which, according to D'Je'rin, originate mainly in the parietal area, according to Monakov in the frontal area and in the operculum, are of great importance. Of the efferent paths, the most ancient phylogenetically rubro-spinal path (fasciculus rubro-spinalis) should be mentioned first, the fibers of which after the decussation go down and end near the cells of the anterior horns of the spinal cord. The second efferent system is the rubrothalamic path, consisting of fibers leaving the anterior pole of the nuclei rubri and directed to the external nucleus of the thalamus. The third efferent system is the central tectal path, the fibers of which take their origin mainly from the thalamus and the subthalamic area (partly from the N. g.) and are directed through the tectum of the midbrain and the pons Varolii, receiving here reinforcements from the reticular formation. The central tectal path ends completely or almost completely in the large cellular accumulation of the medulla oblongata - the inferior olive, which on one side is in connection with the cortex of the cerebellar hemispheres, on the other - with the spinal cord through the Helweg path. According to some authors, part of the fibers of the central tectal path passes directly into the Helweg bundle. Finally, the rubro-cortical paths, mainly the rubro-frontal paths (Monakov), are of great importance. The functions of the red nucleus are of great importance, as can be judged already from its size, from the complexity of its structure, and from the abundance of its connections. First of all, it is a transmitting agency conducting cerebellar impulses to lower motor apparatuses, and thus serves the purposes of coordination. Then (the function of the more phylogenetically young part, the small-cellular oral nucleus) it transmits cerebellar impulses to the cerebral cortex, especially the frontal area. Finally, it is an intermediate apparatus uniting the impulses of the striopallidal system and the cerebellar coordination apparatus and is thus one of the most important agencies of the complex extrapyramidal motor system. - Irritation of the N. g. by electric current in monkeys (Graham, Brown) causes extension of the head, rotation of the face towards the side of irritation, flexion of the homonymous and extension of the crossed upper extremity, and conversely, extension of the homonymous and flexion of the crossed lower extremity, extension and abduction of the tail towards the side of irritation. The motor effect is very tonic, the reaction persists even after the cessation of irritation, in contrast to the reaction to irritation of the pyramidal path, which has a pronounced phasic character. Experiments with transection of the brain stem (Rademaker) showed that in rabbits and cats the large-cellular part of the N. g. represents a center which regulates the normal distribution of tone, and its destruction (or of its efferent paths, the decussation of Forel) leads to the development of decerebrate rigidity (see Decerebration, decerebrate rigidity). In man, as anatomical-clinical observations show, the matter is different: the N. g. does not have such exceptional significance for the normal distribution of tone as in lower animals, hypertension and contractures are not a constant symptom of destruction of the N. g., and sometimes hypotonia is also possible. It is undoubtedly, however, that in man the N. g. also has very great significance in the construction of motor functions, which is proved, on the one hand, by anatomical relations, on the other - by severe disturbances of motility in cases of its lesion, manifested in severe hyperkineses in the form of athetosis, chorea, or tremor (Benedict's oculo-complex with lesion of the oculomotor nerve on the side of the focus and with hyperkineses on the opposite side).