In humans, the red nucleus mainly controls the muscles of the shoulder and upper arm, but it has some control over the lower arm and hand as well. It is less important in its motor functions for humans than in many other mammals, because, in humans, the corticospinal tract is dominant. However the crawling of babies is controlled by the red nucleus, as is arm-swinging in normal walking. Since the red nucleus has sparse control over hands (as the Rubrospinal tract is more involved in large muscle movement such as that for Arms and Legs), fine control of the fingers is not modified by the functioning of the red nucleus (rather it relies on the corticobulbar tract [CoBuTr]).
Input and output
The red nucleus receives many inputs from the contralateral cerebellum 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 nucleus 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.
Meaning of name
Its name derives from an iron-containing pigment in many of the cells, which in fresh samples gives it a pink appearance.