Problem 160 - Objective Biology for NEET

Question

Assertion: No image is formed at the exit of optic nerve. Reason: It lacks the receptor cells and is insensitive to light.

Step-by-Step Solution

Answer

Yes, the assertion and reason are correct. An image is not formed at the exit of optic nerve since it lacks the receptor cells and is insensitive to light. The optic nerve merely transmits the information to the brain where the image is perceived.

Step 1 - Understand The Human Eye Structure

The human eye is a complex organ which reacts to light and pressure. It primarily consists of the cornea, iris, pupil, lens, retina and the optic nerve. The retina contains the receptor cells, which are sensitive to light and the optic nerve sends visual information to the brain.

Step 2 - Compartmentalizing The Descriptions

The assertion here is that no image is formed at the exit of the optic nerve. This is because, the optic nerve does not have light-sensitive cells, it just conducts light information in the form of electric impulses from the retina to the brain.

Step 3 - Connecting Assertion And Reason

The reason provided is optimal as it justifies the assertion appropriately, which is it lacks receptor cells and hence is insensitive to light.

Key Concepts

Optic Nerve

The optic nerve is a crucial component of your visual system. Think of it as the messenger that bridges your eyes and your brain. Its sole mission is to carry the visual information gathered by your eyes to the brain for interpretation. The information is transferred in the form of electrical impulses. Unlike other parts of the eye, the optic nerve is not sensitive to light. This is because it lacks receptor cells, which are crucial for light detection. Instead, its primary purpose is

• To take visual data from the retina.
• Convert this data into electrical signals.
• Send these signals to the brain.

At the point where the optic nerve exits the eye, called the "optic disc," there are no receptor cells. This area is famously known as the "blind spot" because no visual information is processed there.

Retina

The retina is an intricate and vital part of the eye. Located at the back of the eyeball, this thin layer of tissue is responsible for converting light into neural signals. This conversion is a complex process but is essential for vision.

• The retina contains millions of light-sensitive cells called photoreceptors.
• There are two kinds of photoreceptors: rods and cones.
• Rods are more numerous and are better at seeing in low light.
• Cones, on the other hand, detect color and require more light than rods.

Once light touches these cells, it is transformed into electrical impulses. These impulses travel via the optic nerve to the brain, where they are interpreted as images. Without the retina, seeing the world around us would not be possible. It essentially works like a camera sensor, capturing the scenes and images we see every day.

Receptor Cells

Receptor cells in the eye are specialized types of neurons located within the retina. Their primary role is to respond to light and initiate the process of vision. These cells are sensitive to different wavelengths of light, allowing us to perceive color, brightness, and the fine details within our environment.
There are two main categories of receptor cells:

• Rods: These work well in dim light and are primarily responsible for night vision. They do not detect color.
• Cones: These require brighter light and are integral for seeing color and detail.

Rods and cones have different roles but together create the full spectrum of human vision. When light enters the eye, it is these cells that begin the chain reaction of converting light into electrochemical signals. Finally, the signals travel down the optic nerve to the brain. Any area lacking receptor cells cannot perceive light, resulting in spots where no image is formed, such as the blind spot at the optic disc.