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Lab 8 (ƒ7) - Visual System

Gross Anatomy of the Eye - Review

In this section we will trace the optic pathway starting anteriorly in the forebrain and moving posteriorly to the thalamus.

In Figure 1, Layer A you can see the optic nerves converging to form the optic chiasm. Note that this section is taken at the level of the anterior limb of the internal capsule, and that it is identified as such because the internal capsule is bounded superiorly by the caudate head and laterally by the putamen. Recall that corticofugal fibers from the frontal lobe descend in the anterior limb of the internal capsule, and that they include the fibers from the frontal eye field.

Figure 1, Layer B the right side of the brain more rostral than the left. Consequently, the optic chiasm is visible on the inferior surface of the right side of the brain and the optic tract on the left. Recall that the optic nerve fibers from the nasal half of the retina are decussating within the chiasm.

In Figure 1, Layer C notice the optic tracts on either side of the tuber cinereum. The optic tract contains optic nerve fibers from the temporal half of the ipsilateral retina and from the nasal half of the contralateral retina.

In Figure 1, Layer D the optic tract can be seen passing laterally - preparing to enter the thalamus more caudally. The optic tract fibers terminate in the lateral geniculate body (LGB) of the thalamus. Recall that the axons of cortical neurons controlling smooth pursuit eye movements pass through the posterior limb of the internal capsule on their course to the midbrain.

In Figure 1, Layer E the optic tract is approaching or has reached the caudal end of the lateral geniculate nucleus of the thalamus. The lateral geniculate nucleus (LGN) of the thalamus is a laminated nuclear mass just lateral to the cerebral peduncles.

In Figure 1, Layer F notice that the plane of section has changed. The section is now more horizontal than coronal. As its name implies, the lateral geniculate nucleus (LGN) is located lateral to the medial geniculate body.