Direction Of Light

-Inner limiting membrane

Figure 50-2

Photomicrograph of the macula and of the fovea in its center. Note that the inner layers of the retina are pulled to the side to decrease interference with light transmission. (From Fawcett DW: Bloom and Fawcett: A Textbook of Histology, 11th ed. Philadelphia: WB Saunders, 1986; courtesy H. Mizoguchi.)

photochemicals, usually called simply color pigments, that function almost exactly the same as rhodopsin except for differences in spectral sensitivity.

Note in the outer segments of the rods and cones in Figures 50-3 and 50-4 the large numbers of discs. Each of the discs is actually an infolded shelf of cell membrane. There are as many as 1000 discs in each rod or cone.

Both rhodopsin and the color pigments are conjugated proteins. They are incorporated into the membranes of the discs in the form of transmembrane proteins. The concentrations of these photosensitive pigments in the discs are so great that the pigments themselves constitute about 40 per cent of the entire mass of the outer segment.

The inner segment of the rod or cone contains the usual cytoplasm with cytoplasmic organelles. Particularly important are the mitochondria; as explained later, these mitochondria play the important role of providing energy for function of the photoreceptors.

The synaptic body is the portion of the rod or cone that connects with subsequent neuronal cells, the

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