The main input to this nucleus, in humans, comes from the red nucleus. Axons from the red nucleus descend through the center of the brain stem tegmentum in the central tegmental tract. Afferent fibers from the spinal cord synapse in the accessory olivary nuclei. The cells of the inferior olivary nuclei send their axons across the midline to terminate as climbing fibers on Purkinje cells in all parts of the cerebellum.