Final answer:
A rod is a photoreceptor cell in the retina specialized for vision in low light conditions, producing images in gray scales and enabling night vision. Rods are more sensitive to dim light than cones, do not provide color information, and are essential for peripheral vision.
Step-by-step explanation:
A rod is a photoreceptor cell that only produces images in shades of gray, and is responsible for night vision. In the human retina, there are approximately 120 million rods, which are more sensitive to dim light than cones by a factor of about 1000. These cylindrical neurons are situated primarily in the outer edges of the retina and are crucial for peripheral and nighttime vision.
Unlike cones, which are responsible for color vision and respond to intense light, rods are achromatic, meaning they do not provide color information. Instead, they allow us to see in low light conditions by detecting various shades of gray, enabling motion detection and peripheral vision. In very dark environments, you may notice that you lose the ability to see colors but can still discern gray scales, thanks to the function of rods.