Lab 8 - Higher Motor Function

Microscopic Anatomy

Using the images, work along with the coronal slices to identify the structures in bold type.

Figure 1, Layer A: Here the caudate head and the putamen appear nearly fused and comprise the neostriatum. Notice also the size of the frontal or anterior horns of the lateral ventricles. Notice that strips of gray matter run through the anterior limb of the internal capsule, between the caudate head and the putamen giving the region a striped or striated appearance.

Figure 1, Layer B: Locate the lateral ventricle, caudate body, putamen and globus pallidus. The axons of the globus pallidus are collecting in two fiber bundles, the lenticular fasciculus, medially and the ansa lenticularis inferiorly. The projection from the globus pallidus to the thalamus is via the lenticular fasciculus and the ansa lenticularis. Axons of the lenticular fasciculus pass through the internal capsule on the way to the thalamus. Axons of the ansa lenticularis sweep ventrally and medially around medial edge of the posterior limb of the internal capsule. The nuclei of the thalamus that receive the axons of the globus pallidus are the VA, VL, and CM.

Figure 1, Layer C: In the thalamus, the anterior nucleus forms a conspicuous knob on its superior-medial surface and the dorsomedial (DM) nucleus has not yet formed. The nucleus of the lateral thalamic group that is present in this section is the VA. Notice the caudate and putamen (i.e., the neostriatum) which sends axons to the globus pallidus and substantia nigra. Locate the ansa lenticularis, which carries axons from the globus pallidus to the thalamus.

Figure 1, Layer D: Locate the anterior thalamic nucleus, the caudate bodyposterior limb of the internal capsule,globus pallidusputamenand third ventricle.

Locate the caudate bodyglobus pallidus, and putamen which form the corpus striatum. Notice that in the diencephalon the lenticular fascicularis arches inferiorly and joins the ansa lenticularis. The two tracts then pass medially around the zona incerta and join the cerebellothalamic axons (i.e., superior cerebellar peduncle fibers that bypassed the red nucleus). These three tracts ascend to the thalamus as the thalamic fasciculus. Remember that the ansa lenticularis and lenticular fasciculus carry globus pallidus axons to the VA, VL and CM thalamic nuclei and that these thalamic nuclei project back to motor areas in the frontal lobe. Notice the subthalamic nucleus is wedged between the the lenticular fasciculus and the substantia nigra. The subthalamic nucleus receives axons from and sends axons to the globus pallidus. The major input to the substantia nigra arises from the neostriatum. In turn, the substantia nigra sends most of its axons back to the neostriatum and to the VA and VL.