Red nucleus

The red nucleus is a structure in the rostral midbrain involved in motor coordination. It comprises a caudal magnocellular and a rostral parvocellular part.

Function
In animals without a significant corticospinal tract, gait is mainly controlled by the red nucleus.

However, where the corticospinal tract is dominant, the rubrospinal tract may be considered to be vestigial. Therefore, here the red nucleus is less important in motor functions than in many other mammals. However, the crawling of babies is controlled by the red nucleus, as is arm swinging in normal 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 sparse control over hands, as the rubrospinal tract is more involved in large muscle movement such as that for arms (but not 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 (rather it relies on the corticospinal tract). The majority of red nucleus axons do not project to the spinal cord, but instead (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 contralateral cerebellum (interposed nucleus and lateral cerebellar nucleus) and an input from the ipsilateral motor cortex.

It sends efferent axons (the rubrospinal projection) to the contralateral half of the rhombencephalic reticular formation and spinal cord. These efferent axons cross just ventral to the anterior tegmental decussation and descend through the midbrain to the spinal cord, where the rubrospinal tract, which they make up, runs ventral to the lateral corticospinal tract in the lateral funiculus. Second bundle of fibers continues ipsilaterally through the medial tegmental field toward inferior olive.