Which photoreceptor type has higher light sensitivity?

• A. Rods
• B. Cones
• C. Rods and cones
• D. Ganglion cells

Answer: (A)

Light sensitivity describes how faint a light a receptor can detect. Rods are built for night vision, with a high gain in the phototransduction cascade and a pigment called rhodopsin that responds strongly to small amounts of light. Many rods converge onto fewer ganglion cells, so a weak signal is amplified as it travels to the brain, making rods able to detect single photons in darkness. Cones require more light to activate and provide fine detail and color because each cone (or a few cones) connects more directly to a ganglion cell, boosting acuity but reducing sensitivity. Ganglion cells themselves aren’t photoreceptors, so they don’t determine light sensitivity. Thus, the photoreceptor type with higher light sensitivity is rods.