Wednesday, October 12, 2005


The sensory neuroepithelium of the eye is the retina, which is composed of many layers (Figure 2-18). These include the layer of outer and inner segments of the photoreceptor cells (rods and cones), the outer nuclear layer (cell bodies of photoreceptor cells), the outer plexiform layer, the inner nuclear layer, the inner plexiform layer, the ganglion cell layer, the nerve fiber layer, and the inner limiting lamina (membrane). The photoreceptors are composed laminated discs that are connected to cilia with a 9+0 motif. The discs of the cone are connected to the cell membrane whereas rod disks are not. The cilia of both rods and cones connect to mitochondrial rich ellipsoids that are contiguous with myoids. The 120 million rods and 6 million cones synapse with horizontal cells, bipolar cells and other rods and cones. Bipolar cells synapse with ganglion cells, amacrine cells and of course rods and cones. The axons of the ganglion cells form the nerve fiber layer and coalsesce to become the 1 million fibers of the optic nerve. These fibers travel posteriorly to synapse in the lateral geniculate body. Muller cells are supportive cells that extend fibers from the internal limiting membrane to the "external limiting membrane of the retina. The retina is loosely attached to the pigment epithelium, which is separated from the choroid by Bruch’s membrane.
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