| Popis: |
The visual receptor of the vertebrate retina is composed of several specialized compartments as shown in Figure 1. The visual pigment is located in the double membrane discs which, like a stack of coins, fill up the cylindrical (rod) or tapered (cone) outer segment of the receptor cells. The outer segment points towards the pigment epithelium and sciera and is connected to the inner by a narrow cylindrical stalk containing a modified cilium (and is sometimes also connected by an additional cytoplasmic bridge; Richardson, 1969). The scierai part of the inner segment, the ellipsoid, contains numerous mitochondria and apparently constitutes a center of oxidative phosphorylation. The nucleus is located between the inner segment and the complicated synaptic structures connecting the receptor to the horizontal and bipolar cells, which in turn relay the visual signal to the amacrine and ganglion cells (for reviews describing the ultrastructure of vertebrate visual cells, see Sjostrand, 1961; Cohen, 1972). |
