MODULE 14

The FOUR LEVELS of the DORSAL THALAMUS

- - - We have found the following approach to be the easiest way to "organize" the thalamus and identify the nuclei within it. Keep in mind that the goal is to get some idea of where the nuclei actually are and refer to Figure 14-9 as you go along. The box if the lower right corner tries to summarize the situation.

- - - Three planes, A, B and C, serve to divide the thalamus into four regions. Plane A passes through the ascending fibers of the mammillothalamic tract and the rostral edge of medialis dorsalis. Plane B passes through the rostral edge of the centromedian nucleus. Plane C passes through the descending fibers of the habenulopeduncular tract and the caudal edge of the centromedian nucleus.

- - - Region 1 contains the anterior nucleus and ventralis anterior. Medialis dorsalis first appears in region 2; in this region, the anterior nucleus is still present, but ventralis anterior is replace by ventralis lateralis. The development of the centromedian nucleus within the internal medullary lamina, signals the transition to region 3. Lateralis dorsalis replaces the anterior nucleus and ventralis lateralis gives way to the ventralposterior nuclei (medial and lateral). Lateralis posterior lies dorsal to these two nuclei. This disappearance of all these nuclei marks the passage to region 4. This region contains only three nuclei - the pulvinar and the two geniculates.

- - - The reticular nucleus is present in all four regions, and we have omitted it in the above description. Also omitted are the midline nuclei, which lie adjacent to the ventricle, and the posterior nucleus which is found at the junction of regions 3 and 4, placed just medial to the medial geniculate nucleus.

- - - After you have mastered Figure 14-9 and the concept of four thalamic regions, look at the full scale views of the sections most typical of each region. Switch back and forth between the labeled and unlabeled versions until you think you can really identify the nuclei. To call up slides, either use Figure 14-5 or click on the individual slides below.

• Region 1 Cu Slide 36
• Region 2 Cu Slide 32
• Region 3 Cu Slide 28
• Region 4 Cu Slide 24

- - - Finally, review the entire slide series through this part of the brain.

• Cu Slide 38
• Cu Slide 37
• Cu Slide 36
• Cu Slide 35
• Cu Slide 34
• Cu Slide 33
• Cu Slide 32
• Cu Slide 31
• Cu Slide 30
• Cu Slide 29
• Cu Slide 28
• Cu Slide 27
• Cu Slide 26
• Cu Slide 25
• Cu Slide 24
• Cu Slide 23
• Cu Slide 22
• Cu Slide 21
• Cu Slide 20
• Cu Slide 19

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