Unlike most sensory receptors, vertebrate photoreceptors (rods and cones) hyperpolarize in response to light. In darkness, cGMP keeps Na⁺ channels open, keeping the cell relatively depolarized. Light activates rhodopsin → transducin → phosphodiesterase → cGMP breakdown → Na⁺ channels close → membrane hyperpolarizes. This hyperpolarization reduces glutamate release onto bipolar cells, ultimately signalling light detection.