MODULE 14 - SECTION 4 - THE FOUR REGIONS of the DORSAL THALAMUS
THE FOUR REGIONS
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 the figure at left 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.
PLANES and DIRECTIONS
in the
DIENCEPHALON
This figure shows the planes for the next 4 views (slides 24, 28, 32 and 36)
THE THREE THALAMIC NUCLEI
in
REGION 1
This slide passes through the middle of region 1. The fact that only two large nuclei are present (and that medialis dorsalis is obviously lacking) tells us that we are still anterior to region 2. That, in turn, tells us that the more lateral nucleus is ventralis anterior, rather than ventralis lateralis.
THE FOUR THALAMIC NUCLEI
in
REGION 2
This slide has the "classic" appearance of region 2. Only within this region is medialis dorsalis prominent and the centromedian nucleus lacking. The mammilothalamic tract is seen here, close to its origin in the mammillary body. The fasciculus thalamicus, the terminal segment of the pathway passing from the globus pallidus to ventralis anterior, also is present in this slide.
THE SEVEN THALAMIC NUCLEI
in
REGION 3
This slide has the classic appearance of level 3. Arrows show how the fibers leave this part of the thalamus and pass "upward" within the superior thalamic radiation to reach the cortex of the parietal lobe. In doing so, they will run through the posterior limb of the internal capsule.
THE FOUR THALAMIC NUCLEI
in
REGION 4
ENTIRE SLIDE SERIES
The full set of slides that cover this part of the brain are given below (#38-#19) .
THALAMIC NUCLEI in REGION 1
This slide passes through the tip of the anterior pole of the thalamus. Only the anterior nucleus is present, and it is seen only on the right side of the section.
THALAMIC NUCLEI in REGION 1
THALAMIC NUCLEI in REGION 1
THALAMIC NUCLEI
at the border between
REGIONS 1 and 2
THALAMIC NUCLEI in REGION 2
THALAMIC NUCLEI in REGION 2
THALAMIC NUCLEI in REGION 2
THALAMIC NUCLEI in REGION 4
THALAMIC NUCLEI in REGION 4
THALAMIC NUCLEI in REGION 4
THALAMIC NUCLEI in REGION 4
THALAMIC NUCLEI in REGION 4
THALAMIC NUCLEI in REGION 4
THALAMIC NUCLEI in REGION 4
