Which statement accurately describes sensory transduction in vision?

Which statement accurately describes sensory transduction in vision?

• A. Photoreceptors depolarize in response to light, increasing neurotransmitter release.
• B. Photoreceptors hyperpolarize in response to light, reducing neurotransmitter release.
• C. Photoreceptors generate action potentials in response to light.
• D. Photoreceptors release the same amount of neurotransmitter regardless of light.

Answer: (B)

Photoreceptors convert light into a change in membrane potential that is graded, not an all-or-none spike. In darkness, cGMP keeps cGMP-gated Na+/Ca2+ channels open, producing a depolarizing dark current and steady release of glutamate onto downstream neurons. When light hits the retina, a phototransduction cascade lowers cGMP, channels close, the cell hyperpolarizes, calcium entry falls, and neurotransmitter release decreases. This exactly matches the statement: light causes hyperpolarization and reduced neurotransmitter release. The other options don’t fit because photoreceptors don’t depolarize with light to increase transmitter release, they don’t typically generate action potentials in response to light, and neurotransmitter release is not constant but light-modulated.

Photoreceptors convert light into a change in membrane potential that is graded, not an all-or-none spike. In darkness, cGMP keeps cGMP-gated Na+/Ca2+ channels open, producing a depolarizing dark current and steady release of glutamate onto downstream neurons. When light hits the retina, a phototransduction cascade lowers cGMP, channels close, the cell hyperpolarizes, calcium entry falls, and neurotransmitter release decreases. This exactly matches the statement: light causes hyperpolarization and reduced neurotransmitter release. The other options don’t fit because photoreceptors don’t depolarize with light to increase transmitter release, they don’t typically generate action potentials in response to light, and neurotransmitter release is not constant but light-modulated.