Lab 9 - Descending Pathways to the Spinal Cord

Reticulospinal Pathways - Pons

Figure 1 is a transverse section through the caudal pons. The fibers of the pontine reticulospinal tract arise from the pontine reticular formation, remain uncrossed and descend in the medial longitudinal fasciculus. Recall that the pontine reticular formation includes a paramedian cell group that is important for the control of conjugate lateral gaze. This tract extends the entire length of the spinal cord. These reticulospinal tract fibers facilitate voluntary and reflex responses and muscle tone.

Figure 2 is a transverse section through the pontomedullary junction. The fibers of the pontine reticulospinal tract remain in the medial longitudinal fasciculus. The pontine reticulospinal tract forms the major descending component of the medial longitudinal fasciculus.

The medullary reticular formation gives origin to the medullary reticulospinal tract fibers, some of which cross the midline. The medullary reticulospinal fibers pass posterolaterally and take a position lateral to the posterior surface of the inferior olivary nuclei, near the ascending spinothalamic tract and the descending rubrospinal tract. The bilateral but mainly uncrossed medullary reticulospinal tract fibers terminate on neurons at all spinal cord levels and have an inhibitory affect on voluntary and relex responses.