Final answer:
Rods are the photoreceptor cells in the retina that respond to very dim light, being significantly more sensitive than cones. The unique hyperpolarization response of photoreceptors and bipolar cells, in contrast to other sensory receptors, is pivotal for vision in low-light conditions. This system involves lateral inhibition to sharpen image contrast.
Step-by-step explanation:
The photoreceptor cells that respond to very dim light are known as rods. These cells are much more sensitive to light than their counterparts, the cones, by about a thousand times, and are crucial for vision in low-light conditions. Rods do not provide color information but allow us to detect varying shades of grey even when it's dark. They can be found in substantial numbers, with approximately 120 million rods present in the human retina.
Interestingly, the relationship between photoreceptors and adjacent bipolar cells is unique compared to other sensory systems because photoreceptors and bipolar cells tend to be hyperpolarized in response to their stimuli, as opposed to being depolarized like other sensory receptors. This hyperpolarization in the absence of light actively inhibits bipolar cells. Upon exposure to light, this inhibition is lifted, which then allows the now active bipolar cells to stimulate the ganglion cells that send signals to the brain.
Lateral inhibition, facilitated by horizontal and amacrine cells, enhances this process by sharpening the edges and enhancing contrast in the visual images received. The visual system hence relies on changes in retinal activity, encoded by the rate of firing of these cells, to convey visual information to the brain.