Lab 8 - Higher Motor Function

Microscopic Anatomy (continued)

Using the images, work along with the coronal slices to identify the structures in bold type to gain an appreciation of their three dimensional relationships.

Figure 1, Layer A: Anteriorly, the internal medullary lamina encloses the anterior nucleus, separating it from the ventral anterior (VA) nucleus. The VA nucleus only spans a small anterior to posterior distance. The anterior thalamic nucleus receives input from the mammillary bodies and projects to the cingulate gyrus. The VA thalamic nucleus, the most rostral of the lateral thalamic group. It is one of the major thalamic motor nuclei. (HINT-1: When you can see A and there is no DM, the lateral group consists of VA.)

Figure 1, Layer B: Notice that throughout most of the thalamus the internal medullary lamina divides the thalamus into a medial group, consisting of the dorsomedial (DM) nucleus, and a lateral group, consisting of several thalamic nuclei. Here, the lateral group consists of the ventral lateral (VL) nucleus. Note that the VL has replaced the VA, so that the internal medullary lamina now separates the anterior nucleus from the ventral lateral nucleus. (See HINT-1) The anterior nucleus is still present. The DM nucleus receives input from limbic structures and sends its axons chiefly to the prefrontal cortex. The VL nucleus is also a major thalamic motor nucleus. VL is often included with VA and called VA/VL, since both nuclei are involved in motor function. VA/VL receive imput from globus pallidus, substantia nigra and the cerebellar nuclei and sends output to frontal cortex, including motor cortex. (HINT-2: When you can see DM, but not CM or VPM, the lateral group consists of the VL.)

Figure 1, Layer C: Note that the dorsomedial (DM) nucleus of the thalamus is still prominent, the lateral dorsal (LD) nucleus has replaced the anterior nucleus, and the lateral group consists of the LD, lateral posterior (LP) nucleus, ventral posteromedial (VPM) and ventral posterolateral (VPL) nuclei. The centromedian (CM) nucleus is located within the internal medullary lamina and constitutes part of the intralaminar nuclear group. The LP nucleus receives inputs from the superior colliculus, other thalamic nuclei and from the parietal lobe and projects back to the parietal lobe. Its function is not well understood. The LD receives input from the cingulate gyrus and sends output back to the cingulate gyrus. The CM receives input from a number of noncortical sources (e.g., the reticular formation, spinal cord and globus pallidus) and sends its axons to the basal ganglia and to diffuse cortical areas. The CM is believed to be involved in motor function. The VPL receives the ascending fibers of the medial lemniscus and the spinothalamic tract. Recall that the VPM receives the fibers of the ventral trigeminal lemniscus. (HINT-3: When you can see DM, CM and VPM, LD replaces A and the lateral thalamic group consists of the LD, LP, VPM and VPL.)

Figure 1, Layer D: Notice that the DM and LD are not present and that the pulvinar is the most caudal part of the lateral thalamic group. Note the location of the geniculate bodies with respect to the pulvinar. The pulvinar receives input from several sensory systems, and sends axons to the parietal, temporal, and occipital cortices. As you already know, the medial geniculate body is the thalamic sensory nucleus for the auditory system and the lateral geniculate body is the thalamic sensory nucleus for the visual system. The VPL, seen in the third image, receives the ascending fibers of the medial lemniscus and the spinothalamic tract, both of which can be seen here.