Lab 9 - Descending Pathways to the Spinal Cord

Medulla and Cervical Spinal Cord

Figure 1 is a transverse section through the rostral medulla. The rubrospinal tract fibers (crossed) have been shifted posteriorly by the inferior olivary complex, and are medial to the ascending spinothalamic tract and anterior spinocerebellar tract. A useful landmark for locating the rubrospinal tract in the medulla is the spinal trigeminal nucleus, which is located just posterior to it.

Figure 2 is a transverse section through the caudal medulla. The rubrospinal tract remains near the anterior margin of the spinal trigeminal nucleus and medial to the anterior spinocerebellar tract.

Figure 3 is a transverse section through the cervical spinal cord. With the disappearance of the spinal trigeminal nucleus and tract, the rubrospinal tract is now located in the anterior portion of the lateral funiculus. It is anterior to and overlaps part of the area occupied by the lateral corticospinal tract. While the rubrospinal tract descends to all cord levels, most rubrospinal fibers terminate in the cervical cord. These fibers appear to control muscle tone and action of the muscles of the arm, hand, and fingers. They have an excitatory effect on the flexor muscles and an inhibitory effect on the extensor muscles. Also identify the spinal extensions of the other tracts mentioned above: anterior and posterior spinocerebellar tracts, and the (anterior and lateral) spinothalamic tracts.