Where are photopigments primarily located in photoreceptors?

• A. Inner segment
• B. Synaptic terminal
• C. Outer segment discs
• D. Cell body

Answer: (C)

Photopigments are the light-absorbing molecules that trigger vision, and they are located in the outer segment of photoreceptors, specifically within the membranes of the stacked discs. This placement provides a large surface area packed with rhodopsin in rods and cone opsins in cones, maximizing photon capture. When light hits these pigments, the retinal component changes shape and starts a cascade that ultimately alters ion channels and signals the brain. The inner segment houses the cell’s machinery for energy and metabolism, the cell body contains the nucleus, and the synaptic terminal handles neurotransmitter release, but the photopigments themselves sit primarily in the outer segment discs.