Final answer:
Photoreceptors are hyperpolarized by light, which leads to a decrease in the release of glutamate to ON bipolar cells. This causes both the photoreceptors and bipolar cells to undergo changes in voltage.
Step-by-step explanation:
Photoreceptors in the retina are directly affected by light. When light strikes the rhodopsin pigment in photoreceptors, it activates a G-protein called transducin, which in turn activates an enzyme called phosphodiesterase. Phosphodiesterase converts cGMP to GMP, causing sodium channels to close and resulting in a hyperpolarized membrane. This hyperpolarized membrane does not release glutamate to the ON bipolar cells, causing a change in voltage.
In contrast to other sensory receptors, such as those found in touch or taste, which typically remain polarized, photoreceptors and bipolar cells undergo hyperpolarization when exposed to light. This change in membrane potential allows them to transmit visual signals to the brain.
Overall, when exposed to light, photoreceptors are hyperpolarized by the closing of sodium channels, while ON bipolar cells receive less glutamate from the photoreceptors, causing them to also become hyperpolarized and exhibit changes in voltage.