Lab 4 - External and Internal Anatomy of the Spinal Cord

Diencephalon

Finally follow the Posterior Column-Medial Lemniscal pathway in the diencephalon. Use the following text as you navigate through the two cuts through the diencephalon. (Not all of the items in bold will be identified in this slide.)

Midbrain-Diencephalon Junction

This section passes through the junction of the midbrain with the diencephalon. The midbrain structures include the crus cerebrisubstantia nigra, red nucleus, and cerebral aqueduct. Located posterior to the midbrain structures is the thalamus (identified as the pulvinar and ventral posterolateral thalamic nuclei by DeArmond) of the diencephalon. The medial lemniscus is located posterolateral to the red nucleus and continues to carry 2° somatosensory afferents conveying discriminative touch and proprioceptive information from the contralateral body.

Diencephalon

This is a coronal (frontal) section that passes through the rostral midbrain, caudal diencephalon and caudal basal ganglia. The midbrain structures include the crus cerebri (called cerebral peduncles in DeArmond), substantia nigra, and red nucleus. The third ventricle has replaced the cerebral aqueduct. Located posterior to the midbrain structures is the thalamus of the diencephalon. Lateral to the midbrain and thalamus are the posterior limb of the internal capsuleand the caudal remnants of the basal ganglia (i.e., the globus pallidus and putamen). The medial lemniscusextends from the lateral surface of the red nucleus, fans out posterolaterally towards the ventral posterolateral (VPL) nucleus of the thalamus where it terminates. The VPL neurons (3° somatosensory afferents) send their axons in the posterior limb of the internal capsule to the postcentral gyrus of the parietal lobe. Recall that the postcentral gyrus of the parietal lobe constitutes the primary cortical receiving area for the somatosensory systems.