Lab 4 - External and Internal Anatomy of the Spinal Cord

Spinal Cord

This and the next two sections will take you through the Posterior Column Medial Lemniscal Pathway in more detail. In this section, identify the relevant parts of this pathway along with important landmarks at each level of the spinal cord in Figure 1. Starting with the sacral spinal cord. Use the following text as you go through each level.

Sacral Cord

The 1° afferent fibers, which carry discriminative touch and proprioceptive information from the lower body, enter the cord via the posterior root and join the gracile fasciculus. These afferents travel upward in the posterior (dorsal) columns of the spinal cord without synapsing or crossing until they reach their site of termination in the ipsilateral medulla.

Lumbar Cord

As in the sacral cord, the 1° afferent fibers enter the gracile fasciculus and are traveling upward in the posterior (dorsal) columns to their site of termination in the ipsilateral medulla.

Thoracic Cord

In the thoracic cord, the 1° afferent fibers may enter the gracile or cuneate fasciculi. Fibers entering in segments T6 and below ascend in the gracile fasciculus. Fibers entering above T6 travel in the cuneate fasciculus. Both sets of axons ascend the length of the spinal cord uncrossed in the posterior (dorsal) funiculus to terminate in the ipsilateral medulla. Notice that a funiculus consists of (i.e., contains) a number of individual fasciculi (i.e., tracts).

Cervical Cord

At and above the level of T6, the central processes of the 1° afferents collect lateral to the posterior intermediate sulcus, within the cuneate fasciculus. Fibers from the lower segments are still collected within and ascending in the gracile fasciculus. The gracile fasciculus and cuneate fasciculus collectively form the posterior funiculus, which is also called the posterior (dorsal) column.