Final answer:
Photoreceptors and bipolar cells in the retina are unique because they become hyperpolarized in response to light, reducing neurotransmitter release and activating bipolar cells, which is the opposite of the typical depolarization seen in other sensory receptors.
Step-by-step explanation:
The relationship between photoreceptors and bipolar cells is unique compared to other sensory receptors and their adjacent cells. In the retina, the photoreceptors (rods and cones) are involved in tonic activity, meaning they are always slightly active, even in the absence of light. When there is no light, photoreceptors release neurotransmitters that inhibit bipolar cells. In the presence of light, photoreceptors undergo hyperpolarization, which reduces their release of neurotransmitters and consequently allows bipolar cells to become active. This contrasts with other sensory systems where receptors typically become depolarized when stimulated. The bipolar cells then relay the visual information to ganglion cells, which transmit to the brain through the optic nerve.
A key feature of visual processing is lateral inhibition, mediated by horizontal cells, that enhances contrast and sharpens images by making lit areas appear brighter and dark areas darker.In short, the distinguishing factor is that photoreceptors and bipolar cells are hyperpolarized in response to stimuli (light), whereas other sensory receptors are typically depolarized upon stimulation.