Question

i.Blind spot in vertebrate eye is the place where (a) there are no cones (b) there are no rods (c) there are neither rods nor cones d) retina is absent.

Short answer

The correct answer is (c) there are neither rods nor cones.

Step-by-step solution

Identify the Function of the Blind Spot

The blind spot in the vertebrate eye is a specific point at which the optic nerve passes through the layer of the retina. At this point, there are no photoreceptor cells, meaning that no visual information is detected.

Differentiate Between Rods and Cones

Understand that rods and cones are the two types of photoreceptor cells in the retina. Rods are responsible for low-light vision, while cones are for color and sharpness of vision.

Determine the Correct Option

Since rods and cones are types of photoreceptor cells and the blind spot is the area where there are no photoreceptor cells, the correct answer is the choice that states where neither rods nor cones are present.

Key concepts

Understanding Photoreceptor Cells

Photoreceptor cells are a crucial component of the vertebrate eye, as they are responsible for converting light into neural signals that the brain can understand. There are two primary types of photoreceptor cells: rods and cones.

Rods are highly sensitive to light, which allows them to perform well in dim lighting conditions. However, they do not provide color information. On the other hand, cones require more light and are used for perceiving fine details and colors. The human eye contains three types of cones, each sensitive to different wavelengths corresponding to red, green, and blue light.

The distribution of rods and cones across the retina is not uniform. The highest concentration of cones is found in the macula's center, known as the fovea, which is the region responsible for sharp central vision. Whereas rods are distributed more towards the periphery of the retina, playing a significant role in peripheral and night vision.

The Role of the Optic Nerve in Vision

The optic nerve is like a high-capacity cable that transmits visual information from the eye to the brain. It is formed by the bundling of axons from the ganglion cells in the retina. These ganglion cells receive input from the photoreceptor cells via intermediary cells, including bipolar and amacrine cells.

Where the optic nerve exits the eye is known as the optic disc. This spot lacks photoreceptors because it is occupied by the nerve fibers and blood vessels that supply nourishment to the retina. As a result, this area, referred to as the blind spot, cannot detect light and thus creates a small gap in our visual field. The brain usually compensates for this lack of visual information by filling in the gap with surrounding details and information from the other eye, making the blind spot typically unnoticed.

Contrasting Rods and Cones

Rods and cones both serve as vital photoreceptors in the eye but have distinct roles and are structured differently to fulfill these roles. Rods are elongated and slender and packed with many stacks of membrane-bound discs that contain the photopigment rhodopsin. This structure enhances their ability to capture scarce photons of light, making them extremely sensitive even in low-light conditions.

Cones, in contrast, have a tapered shape and contain different photopigments, which are sensitive to specific wavelengths of light. This allows for the perception of different colors. Additionally, cones are associated with the ability to discern fine details due to their direct connection to individual neurons, allowing for a one-to-one signal transmission that is crucial for high visual acuity.

Their differences in sensitivity to light and ability to discern detail and color are why rods dominate in night vision and peripheral vision tasks, while cones are primarily used during daylight and for tasks requiring high-resolution vision, such as reading.