The illustrations of the sensory and motor pathways in this section of the atlas are all done in a standard manner:
• On the left side, the CNS is depicted, including spinal cord, brainstem, thalamus, and a coronal section through the hemispheres, with small diagrams of the hemisphere at the top showing the area of the cerebral cortex involved.
• On the right side, cross-sections (X-sections) of the brainstem and spinal cord, at standardized levels are depicted; the exact levels are indicated by arrows on the diagram on the left. In all, there are 10 cross-sections — 8 through the brainstem and 2 through the spinal cord. For each of the pathways, 5 of these will be used.
The diagram of the hemispheres is a coronal section, similar to the one already described in Section A, at the plane of the lenticular nucleus (see Figure 29). Note the basal ganglia, the thalamus, the internal capsule, and the ventricles; these labels will not be repeated in the following diagrams. This diagram will be used to convey the overall course of the tract and, particularly, at what level the fibers cross (i.e., decussate).
The X-sections (cross-sections) of the brainstem and the spinal cord include:
• Two levels through the midbrain — upper and lower
• Three levels through the pons — upper, mid, and lower
• Three levels through the medulla — upper, mid, and lower
• Two levels through the spinal cord — cervical and lumbar
The exact position of the tract under consideration is indicated in these cross-sections. It is important to note that only some of the levels are used in describing each of the pathways.
These brainstem and spinal cord cross-sections are the same as those shown in Section C of this atlas (see Figure 64-Figure 69). In that section, details of the histological anatomy of the spinal cord and brainstem are given. We have titled that section of the atlas Neurological Neu-roanatomy because it allows precise location of the tracts, which is necessary for the localization of an injury or disease. The learner may wish to consult these detailed diagrams at this stage.
Studying pathways in the central nervous system necessitates visualizing the pathways, a challenging task for many. The pathways that are under study extend longitudinally through the CNS, going from spinal cord and brainstem to thalamus and cortex for sensory (ascending) pathways, and from cortex to brainstem and spinal cord for motor (descending) pathways. As is done in other texts and atlases, diagrams are used to facilitate this visualization exercise for the learner; color adds to the ability to visualize these pathways, as does the illustration on a CD-ROM.
This section is a foundation for the student in correlating the anatomy of the pathways with the clinical symptomatology.
Note to the Learner: In this presentation of the pathways, the learner is advised to return to the description of the thalamus and the various specific relay nuclei (see Figure 12 and Figure 63). Likewise, referring to the cortical illustrations (see Figure 13-Figure 17) will inform the learner which areas of the cerebral cortex are involved in the various sensory modalities. This will assist in integrating the anatomical information presented in the previous section.
T = Thalamus
C = Caudate P = Putamen G = Globus pallidus
LV = Lateral Ventricle 3 = 3rd Ventricle
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