Principles of Physiology and Biochemistry Vision

The Visual Pigments Are Found in Rod and Cone Cells Rhodopsin Consists of 11-cri-Retinal Bound to the 

Changes in Its Absorption Spectrum Isomerization of the Retinal Causes Other 

Structural Changes in the Protein The Conductivity Change That Results from Absorption 

The light traverses an aqueous chamber and reaches the lens, which is densely packed with proteins called crystal-lins. Adjustments in the shape of the lens focus a sharp optical image onto the retina, a thin layer of tissue that lines the back of the eye. The retina is a neural tissue with several different layers of cells. Some of these cells, the rod and cone cells, contain the visual pigments. Other cells make synaptic connections to the rods or cones and to additional neural cells that carry impulses to the brain. 

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. 

---

Part 6 concludes with two brief, informative supplements that integrate physiological and biochemical principles as they apply to the nonmetabolic functions of amino acids and lipids Supplement 1 —Principles of Physiology and Biochemistry Neurotransmission and Supplement 2—Principles of Physiology and Biochemistry Vision. 

---