Lab 9 - Descending Pathways to the Spinal Cord

Diencepalon/Midbrain Junction

Figure 1 shows a coronal section through the diencephalon/midbrain junction. The red nucleus, which contains the cells of origin of the rubrospinal tract, can be seen ventral to the thalamus. The major inputs to the red nucleus include the cerebellum (interposed and dentate nuclei) and the cerebral cortex (motor and premotor areas). The band of fibers coursing towards the red nucleus lateral surface includes corticorubral fibers that arise in the cerebral cortex and terminate in the red nucleus. The fiber capsule surrounding the red nucleus includes the crossed superior cerebellar peduncle fibers that also terminate in this nucleus.

Figure 2 is a transverse section through the diencephalon/midbrain junction. The red nucleus is larger than at more rostral levels and continues to be surrounded by the crossed superior cerebellar peduncle fibers. Its cells are receiving terminals from the corticorubral tract and the superior cerebellar peduncle. Some axons of the superior cerebellar peduncles continue rostrally to terminate in the VL nuclei of the thalamus. Some of the cells of the red nucleus give rise to fibers that pass anteromedially, decussate and collect to form the rubrospinal tract.