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This file will help you tolearn about rod cell in retine-eyes.
Cones are similar, differing principally in the shape of the light-sensitive outer segment. The rod is the "model" photosensitive transducer, and in discussing the actual events of transforming light energy into neural impulses, the rod will be used as an example.
The constricted waist of the rod cell is the location of its fusions with the Muller cells to form the outer limiting "membrane" that seals off the sensitive inner portions of this neuronal cell from the outside world. The rod is "polarized," in that its outer end is greatly different in structure and function from the inner one. The inner end of the rod cell, the synaptic end is its variant form of axon. The synaptic end of the rod makes contact with horizontal and bipolar cells in the outer plexiform layer; the somata of the rods (and cones), containing their nuclei, comprise the outer nuclear layer.
Because the rod is in essence a neuron, its isolation by the glia-like Muller cells is necessary. But the ends of the outer segment, in which lie the stacks of light-sensitive membrane, must periodically be renewed. This is the job of the pigment epithelium layer. As they wear out, the pigment epithelium phagocytoses the ends of the outer segments, and new membrane material is added at the inner end. Thus the rod is refreshed and always ready to respond to light. The lipofuscin in the pigment epithelium layer is the indigestible residue of this activity; it helps to dampen reflections, though its role in this process is less important than the melanin of the choroid layer of the uveal tunic.
