Rubrospinal tract

At a glance

English

Rubrospinal tract

Latin (TA2)

Tractus rubrospinalis

System

Nerve

Region

Whole body

Side

Single, on the midline

About the rubrospinal tract

Lying outside the pyramids, the rubrospinal tract is a descending motor pathway, and with the corticospinal tract it forms the lateral group of motor pathways that govern the limbs. It begins in the red nucleus, an oval mass in the tegmentum of the midbrain at the level of the superior colliculus. Its fibres come from the large-celled, or magnocellular, part of the nucleus, which in humans is small compared with the parvocellular part.

Soon after leaving the nucleus the fibres cross the midline in the ventral tegmental decussation. They then descend through the lateral tegmentum of the pons and medulla and enter the cord, where in the lateral funiculus they run just in front of and partly mixed with the lateral corticospinal tract. In humans most fibres stop in the cervical and upper thoracic cord. They end on interneurons in the intermediate grey matter and the base of the posterior horn, and through them influence motor neurons of the upper limb.

The red nucleus receives input from the motor cortex and from the deep nuclei of the cerebellum, so the tract offers a second, indirect route by which these centres reach the cord. Its effect is to support activity in flexor muscles and to restrain extensors, mainly in the arm and hand. It helps with the control of limb movement, but in humans its share of motor control is modest; the tract is smaller and carries fewer axons than the corticospinal system and is often described as rudimentary.

In other primates, if the corticospinal tract is damaged, the rubrospinal pathway can take over a large part of its work with time. This shift is one reason the tract attracts interest in studies of recovery. The flexed arm posture seen in decorticate states has also been linked to the rubrospinal pathway being left without cortical control.

Course and supply

Supplies

Facilitates flexor and inhibits extensor motor neurons of the opposite upper limb, assisting in the control of limb movement.

Blood supply

Runs in the lateral funiculus, supplied by the anterior spinal artery and the arterial vasocorona.