THE DESCENDING PATHWAYS TO THE SPINAL CORD, THEIR ANATOMY AND FUNCTION.

Publisher Summary This chapter discusses the descending pathways to the spinal cord. These pathways can be grouped according to their origin into two categories: (1) those coming from the cerebral cortex and (2) those coming from the brain stem. The cortico-spinal fibers appeared to be derived primarily from the pericruciate cortex in the cat and from the pericentral cortex in the Rhesus monkey. Ablation-degeneration studies in both animals demonstrated that the cortico-spinal fibers are distributed to the nuclei cuneatus and gracilis and to the spinal gray matter. In regard to the latter distribution, the cortical fibers in the cat terminate, primarily, in the nucleus proprius of the dorsal horn, and the intermediate zone. Only a few fibers spill over into the territory of the ventral horn and none are distributed to the motoneuronal cell groups. In the lower brain stem system of fibers that descended throughout the spinal cord via the lateral funiculus, distributed among to the lateral reticular formation and to some cranial motor nuclei. In the spinal cord, the bulk of this system appeared to be directed to the cervical segments, as only few fibers were found in the lumbo-sacral segments despite the damage to the rubro spinal tract.