This is the process of converting light into electrical potentials for nerves.
Transduction in the Rod
Phototransduction refers to how the light is converted into an electrical signal.
Dark
Retinal is a molecule that changes configuration depending on its exposure to light. When in the dark, its in the 11-cis configuration. Its also connected to a counterpart called opsin and together they form Rhodopsin Phosphodiesterase is an enzyme that is designed to breakdown cyclic nucleotides (the specific one of note is cGMP which is known as cyclic guanosine monophosphate). In the dark, this enzyme is inactive, causing the rod’s inside to have a high concentration of cGMP. cGMP binds to ion channels on the membrane of the rod which lets in a bunch of s Sodium and Calcium.
Light
When light is introduced to a rod, its retinal changes shape into the all-trans form. Which changes the entire Rhodopsin molecule to metarhodopsin II. This sends our the messenget G Protein to activate Phosphodisterase to start changing cGMP to GMP. The reduction of cGMP makes the Ion channels in the wall of the rod to close, which causes the entire rod to hyperpolarize.
In cones, the mechanism is the same thing, expect with a different kind of opsin for red, greed and blue.