Lab 9 - Descending Pathways to the Spinal Cord

The Corticospinal Pathway - Rostral Midbrain

Figure 1 is a transverse section through the brainstem at the level of the diencephalic-midbrain junction. Locate the thalamus (pulvinar, Medial Geniculate Body, and Lateral Geniculate Body), red nucleus, and substantia nigra.

The corticospinal fibers have joined the corticorubral, corticobulbar and corticopontine fibers to form the cerebral peduncle (crus cerebri) of the midbrain.

Figure 2 is a transverse section through the midbrain at the level of the caudal superior colliculus. Locate the medial longitudinal fasciculus, red nucleus, substantia nigra, and the superior colliculus. Parts of the Medial Geniculate Body can also be seen here.

The fibers of the corticospinal tract are located within the cerebral peduncle (crus cerebri) along with those of the corticopontine and corticobulbar tracts. The fibers of the corticospinal tract are somatotopically organized: those fibers concerned with the lower extremity are located laterally while those concerned with the upper extremity and head are located more medially.