Flechsig's Tract

FLECHSIG'S TRACT, syn. dorsal spinocerebellar tract, s. fasc. spino-cerebellaris dorsalis, is located in the central nervous system and is an afferent tract in the cerebellar reflex arc. Flechsig's tract begins at the border of the lumbar and thoracic segments in the cells of Clarke's column, located at the base of the posterior horn, near its inner surface. Clarke's column extends in the spinal cord from the third thoracic to the lumbar segments; it reaches its maximum development in the lower thoracic segments; in other parts of the spinal cord, in the cervical and sacral regions, only separate groups of cells are found in the corresponding places—Stilling's cells, which are considered a continuation of Clarke's column. The cells of this column are quite large—40–80 µm, rich in dendrites, and contain much pigment. A portion of the posterior root fibers terminates at the cells of Clarke's column; the fibers of Flechsig's tract, which begin in these cells, cross the posterior horn and then run upward along the periphery of the lateral column, outward from the lateral pyramidal tract, anterior to the posterior horns, and posterior to Gowers' tract, into which Flechsig's tract transitions without sharp boundaries. Flechsig's tract initially increases rapidly in size due to the addition of new fibers, but from the cervical segment of the spinal cord, as Clarke's column decreases, its growth also diminishes, yet it still continues to receive fibers from Stilling's cells. Posteriorly, fibers originating in the cells of Stilling in the lumbosacral region of the spinal cord join Flechsig's tract, which constitute the "Rothmann's sacrocerebellar system" (Rothmann). In the medulla oblongata, Flechsig's tract also lies along the periphery of the lateral column, gradually becomes thicker and less stretched along the periphery, and anteriorly merges with Gowers' tract; in the middle sections of the medulla oblongata, its fibers begin to deviate posteriorly, curving around the outside of the descending root of the trigeminal nerve in the form of external anterior arcuate fibers, gradually approaching the external cuneate nucleus (nucl. extern. cuneati, s. Burdachi) and taking part in the formation of the restiform body, the main part of the inferior cerebellar peduncle. The external nucleus of Burdach, according to some authors, represents an analogy to the group of Clarke's cells; it replaces Clarke's column, which is absent in the cervical region, and serves as a connecting link between the long fibers of the posterior roots running in the posterior columns and the restiform body. In the restiform body, Flechsig's tract occupies a central position; together with it, it enters the cerebellum and terminates in the cortex of the vermis, partly on its own side and partly on the opposite side. Flechsig's tract is an afferent system of the cerebellum, to which it transmits irritations or impulses from the periphery from the skin of the entire body and from deep tissues associated with movement (muscles, tendons, bones), received by it through the fibers of the posterior roots, thanks to which the cerebellum is informed about the position of the body in space and about all changes in this position. These impulses maintain tonic excitation in the cerebellum, which exerts an influence on muscle tone and the function of maintaining equilibrium that depends on it. In the case of disease of Flechsig's tract, the cerebellum does not receive impulses from the periphery, and therefore its tonic influence on the muscles is switched off and equilibrium is disturbed.