Lab 9 - Descending Pathways to the Spinal Cord

Spinal Cord

The figures show the spinal cord starting from the sacral region. As you move down track the corticospinal tract and associated structures. The associated structures seen at all levels are the following: anterior funiculus, anterior horn, anterior median fissure, anterior white commissure, central canal, fasciculus gracilis, gray commissure, intermediate gray, lateral funiculus, nucleus posteromarginalis, nucleus proprius, posterior funiculus, substantia gelatinosa, and the tract of Lissauer. View and identify the structures in the illustration.

Figure 1, Layer A is a transverse section through the sacral spinal cord. Locate the tract of Lissauer, nucleus posteromarginalis, substantia gelatinosa, nucleus proprius, intermediate gray (which at this level contains parasympathetic preganglionics) gray commissure, central canal, anterior horn, anterior funiculus, lateral funiculus, and posterior funiculus. The lateral corticospinal tract occupies most of the posterolateral half of the lateral funiculus. Recall that the posterior spinocerebellar tract is absent at sacral levels.

Figure 1, Layer B is a section through the lumbar spinal cord at or near L2 (notice the reduced size of the dorsal nucleus of Clarke and the large lateral cell group. The axons of the lateral corticospinal tracts influence the activity of the laterally located anterior horn cells. Recall that within the anterior horn the more posterior groups of cells supply flexors and the more anterior cell groups supply the extensors. The few remaining fibers of the anterior corticospinal tract continue to descend in the anterior funiculus.

Figure 1, Layer C You should recognize this as a transverse section through the thoracic spinal cord. Lateral corticospinal fibers continue to terminate in the gray matter of the cord. This pathway is important for the voluntary control of the limbs and digits. Only a few fibers of the anterior corticospinal tract extend beyond the upper thoracic levels.

Figure 1, Layer D This is a transverse section through the cervical enlargement. Locate the intermediate gray, anterior horn, fasciculus gracilis, fasciculus cuneatus, anterior funiculus, lateral funiculus, and anterior median fissure.