1

Metarhodopsin a

Retinene

Opsin

Vitamin A

Centriole (basal body)

permeability decreased

Figure 2.32 Visual Receptors

The rods and cones of the retina transduce light into electrical signals. As illustrated for the rod, light is absorbed by rhodopsin, and through the second messenger cGMP (not shown), Na+ channels in the membrane close and the cell hyperpolarizes. Thus, in the dark the cell is depolarized, but it is hyperpolarized in the light. This electrical response to light is distinct from other receptor responses, in which the response to a stimulus results in a depolarization of the receptor cell membrane.

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