Lab 9 - Descending Pathways to the Spinal Cord

The Corticospinal Pathway - Forebrain

Figure 1 is a coronal section through the rostral diencephalon and basal ganglia at the level of the tuber cinereum. Locate the caudate (body), stria terminalis, thalamus (Anterior and Ventral Anterior nuclei), internal capsule posterior limb, insula, extreme capsule, claustrum, external capsule, putamen, globus pallidus, ansa lenticularis, amygdala, lateral ventricle, and the third ventricle.

The fibers of the neurons in the precentral gyrus (motor cortex), frontal lobe, and parietal lobe enter the corona radiata, a radiating mass of white matter converging toward the internal capsule. At this level, the fibers form part of the posterior limb of the internal capsule, along with other descending and ascending fibers.

Figure 2 is a coronal section through the junction of the diencephalon and midbrain. Locate the caudate (body and tail), stria terminalis, thalamus (Lateral Dorsal, Dorsomedial, Lateral Posterior, Ventral Posterolateral, Ventral Posteromedial, Centromedian nuclei), internal medullary lamina, and substantia nigra.

The descending corticospinal, corticorubral, corticopontine and corticobulbar fibers travel in the internal capsule posterior limb to the cerebral peduncle (crus cerebri) of the midbrain.