Which pair describes the two states of rod photoreceptor cells?

• A. Active and inactive
• B. Dark state (depolarized) and light state (hyperpolarized)
• C. Excited and resting
• D. Rapid and slowly adapting

Answer: (B)

Rod photoreceptors switch between two states defined by their membrane potential. In darkness, cGMP levels stay high, keeping cGMP-gated channels open, which allows a steady influx of Na+ (and Ca2+) and depolarizes the cell, leading to continuous glutamate release onto bipolar cells. When light is present, a phototransduction cascade lowers cGMP, channels close, and the cell hyperpolarizes, reducing transmitter release. This dark state is depolarized, while the light state is hyperpolarized, matching how light information is conveyed through changes in neurotransmitter signaling. The other phrases don’t capture this specific voltage-based dichotomy, and since rods use graded potentials rather than action potentials, terms like excited/resting or rapid/slowly adapting don’t describe the two true states.