Intro | Visual Cortex | Lateral Geniculate Nucleus | Optic Nerve | Retina | Thalamus
Part 1: Image-Mapped Tutorial
Part 2: Matching Self-Test
Part 3: Multiple-Choice Self-Test
The Lateral Geniculate Nucleus is a part of the thalamic sensory relay system. A lateral geniculate nucleus is located on either side of the rear end of the thalamus. All visual information leaving the retina stops at this nucleus for processing before sent to the primary visual cortex. The lateral geniculate nuclei are located beyond the optic chiasm in the visual pathway and, therefore, receive information from the opposite visual field exclusively.
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The lateral geniculate nucleus (LGN) has been the target of extensive research for a number of years. This nucleus is organized in six layers, shaped to look very much like a finger print. The receptive fields of cells in the LGN exhibit the same concentric on-off characteristics as those of retinal ganglion cells. Four of the LGN layers (parvocellular layers 3 to 6) have small receptive fields with input primarily from cones and the X-cells of the ganglion layer. These cells are responsive to color, fine detail, and slowly moving objects. The two additional LGN layers (magnocellular layers 1 and 2) have large receptive fields, process light/dark information from rods and Y-cells of the ganglion layer, and are very sensitive to movement.
The exquisite organization of the LGN provides a good example of the topographic organization of other regions of the cerebrum; the spatial organization used to represent various aspects of the outside world. Cells in the six layers that align have receptive fields in the same area of the retina. In addition, the optic nerve fibers from the two eyes project to distinct layers of LGN. Fibers from the eye on the same side project to layers 2, 3, and 5 of LGN, whereas fibers from the opposite eye project to layers 1, 4, and 6. The reasons why the LGN is organized in this fashion are unknown.