Cilia plasma membrane

In both rods and cones, the light-sensitive molecules reside in a layered system of membranes at one end of the cell (figs. S2.2 and S2.3). The membranes form by invaginations of the plasma membrane near the middle of the cell. In cone cells, the membranes remain contiguous with the plasma membrane. In rods, they pinch off to form a stack of autonomous flattened vesicles, or disks, in the outer segment of the cell. This region of the cell is connected by a thin cilium to the inner segment, which is packed with mitochondria and ribosomes. The basal part of the cell ends in a synaptic junction with another neural cell called a bipolar cell. 

In general, cilia are widespread finger-like cell appendages. The structure of a proto-typic motile cilium is characterized as follows the ciliary shaft originates from a basal body complex in the apical cytoplasm beneath the plasma membrane (Figure 2A). 

The smooth flexible surface of the erythrocyte plasma membrane allows the cell to squeeze through narrow blood capillaries. Some cells have a long, slender extension of the plasma membrane, called a cilium or flagellum, which beats in a whiplike manner. This motion causes fluid to flow across the surface of an epithelium or a sperm cell to swim through the medium. The axons of many neurons are encased by multiple layers of modified plasma membrane called the myelin sheath. This membranous structure is elaborated by... 

One end of the inner segment makes synaptic contact with horizontal and bipolar cells, while the other is connected to the rod outer segments (ROS) via a short connecting cilium. The ROS are made up of hundreds of membraneous discs. Each is free-floating and apparently does not contact other discs or the plasma membrane. 

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