Red nucleus
The red nucleus or nucleus ruber is a structure in the rostral midbrain involved in motor coordination. The red nucleus is pale pink, which is believed to be due to the presence of iron in at least two different forms: hemoglobin and ferritin. The structure is located in the tegmentum of the midbrain next to the substantia nigra and comprises caudal magnocellular and rostral parvocellular components. The red nucleus and substantia nigra are subcortical centers of the extrapyramidal motor system. Function. In a vertebrate without a significant corticospinal tract, gait is mainly controlled by the red nucleus. However , in primates, where the corticospinal tract is dominant, the rubrospinal tract may be regarded as vestigial in motor function. Therefore, the red nucleus is less important in primates than in many other mammals. Nevertheless, the crawling of babies is controlled by the red nucleus, as is arm swinging in typical walking. The red nucleus may play an additional role in controlling muscles of the shoulder and upper arm via projections of its magnocellular part. In humans, the red nucleus also has limited control over hands, as the rubrospinal tract is more involved in large muscle movement such as that for  the arms (but not for the legs, as the tract terminates in the superior thoracic region of the spinal cord). Fine control of the fingers is not modified by the functioning of the red nucleus but relies on the corticospinal tract. The majority of red nucleus axons do not project to the spinal cord but, via its parvocellular part, relay information from the motor cortex to the cerebellum through the inferior olivary complex, an important relay center in the medulla. Input and output. The red nucleus receives many inputs from the cerebellum (interposed nucleus and the lateral cerebellar nucleus) of  the "opposite" side and an input from the motor cortex of the "same" side. The red nucleus has two sets of efferents: