Which photoreceptors have the higher sensitivity of detecting light?

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

Answer: (A)

Rods are the most sensitive to light. They’re designed for low-light (scotopic) vision, so a single photon can influence a rod enough to trigger a signal. This high sensitivity comes from several features: rods have a lot of photopigment (rhodopsin) and a large outer segment that captures more light, and the phototransduction cascade in rods provides strong amplification. Additionally, many rods converge onto a smaller number of downstream neurons, boosting the chance that a dim signal gets sent onward.

Cones, by contrast, need brighter light to react and are optimized for color and fine detail; they have less convergence and less photopigment per cell, which raises the threshold for activation but improves acuity in bright conditions. Ganglion cells aren’t photoreceptors at all; they’re the output neurons that convey signals from the photoreceptors to the brain.