The Rubrospinal Tract Is a Lateral Brainstem Motor Pathway That Can Control Distal Limb Musculature Associated with Skilled Movement

As noted, the reticulospinal, vestibulospinal, and tectospinal tracts are medial descending brainstem motor pathways whose axons run rostrocaudally within more medial portions of the spinal white matter and synapse in more medial por­tions of the spinal gray matter.

The rubrospinal tract axons originate in cells of the red nucleus (nucleus ruber) of the mesencephalon. The red nucleus receives a very significant descending input from higher levels of the motor system hierarchy in the cerebral cortex. This cortico-rubrospinal route provides a means for the motor cortices to influence indirectly the spinal lower motor neurons that operate the distal limb flexor musculature. Therefore the cortico-rubrospinal route is involved in the voluntary control of musculature that participates in skilled, often manipulative movements of the extremities (although not in the most dex­terous movements of the digits). The rubrospinal tract is more important for these types of movements in quadrupeds com­pared with primates. In primates, direct projections from motor cortices to the spinal cord (the corticospinal tract, described next) are more important than the rubrospinal tract in the con­trol of voluntary skilled movement of the extremities. As for most nuclei giving rise to tracts that play a direct role in move­ment, the red nucleus also receives a significant input from the cerebellum. The role of the cerebellum in motor control is briefly described later and in more detail in Chapter 12.