All of the following statements about photoreceptor structure and function are correct EXCEPT:

Explanation

## Photoreceptor Structure and Function ### Rod vs. Cone Sensitivity and Function **Key Point:** Cones are LESS sensitive to light than rods, not more sensitive. Rods are exquisitely sensitive and function under scotopic (low-light) conditions, while cones require higher light intensities and mediate photopic (bright-light) vision and color discrimination. **High-Yield:** The relative sensitivity difference is approximately 1000-fold; a single photon can activate a rod, but cones require multiple photons for meaningful response. ### Why the Correct Answer (Option 1) is Wrong Option 1 reverses the fundamental sensitivity relationship: - **Rods:** ~120 million per retina, exquisitely sensitive, monochromatic (scotopic vision), contain rhodopsin - **Cones:** ~6 million per retina, less sensitive, color-sensitive (three types: L, M, S), contain cone opsins ### Verification of Other Options | Feature | Option 0 | Option 2 | Option 3 | |---------|----------|---------|----------| | **Rhodopsin & G-protein coupling** | ✓ Correct | — | — | | **Outer segment discs** | — | ✓ Correct | — | | **Light → hyperpolarization → ↓ glutamate** | — | — | ✓ Correct | **Clinical Pearl:** The phototransduction cascade is unique because light causes hyperpolarization (opposite to most sensory receptors), which decreases neurotransmitter release and allows ON-center bipolar cells to depolarize. **Mnemonic:** **LIGHT = QUIET** (Light hyperpolarizes → Quiet/reduced glutamate release) [cite:Guyton & Hall Ch 51]