Retinal Photoreceptors: Rods and Cones

There are two types of photoreceptor cells: rods and cones. Rod cells are long, narrow cells that contain the photopigment rhodopsin. Rhodopsin is concentrated in a rod-shaped region of folded membrane discs on the exterior-facing end of the rod cells. The middle of the rod cell contains the nucleus, mitochondria, and most other organelles, while the interior end widens to form a synaptic terminal. Cone cells are shaped similarly to rod cells, but the exterior-facing end of the cell is shaped like a cone. This cone is made of cell membrane folded over itself many times and contains red, green, or blue opsin photopigment.

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