Problem 106 - Objective Biology for NEET

Question

Arrange the following steps of mechanism of vision in order. (1) Light induces dissociation of the retinal from opsin. (2) Change in the structure of opsin. (3) Change in membrane permeability. (4) Potential differences are generated in photoreceptor cells. (5) Generation of AP is ganglion cell through bipolar cells. (6) AP is transmitted via optic nerve to visual cortex. (7) At visual cortex, nerve impulses are analysed and the image formed on retina is recognized based on the earlier memory and experience. (8) Focusing of visible light on retina. (a) \(8,1,2,3,4,5,6,7\) (b) \(8,1,7,2,6,3,5,4\) (c) \(1,2,3,4,5,6,7,8\) (d) \(8,7,6,5,4,3,2,1\)

Step-by-Step Solution

Answer

The correct sequence of events in the mechanism of vision is represented by the option (a) \(8,1,2,3,4,5,6,7\).

Step 1: Recognize the correct sequence

The correct sequence of events in the mechanism of vision is: Focusing of visible light on retina -> Light induces dissociation of the retinal from opsin -> Change in the structure of opsin -> Change in membrane permeability -> Potential differences are generated in photoreceptor cells -> Generation of AP in ganglion cell through bipolar cells -> AP is transmitted via optic nerve to visual cortex -> At visual cortex, nerve impulses are analyzed and the image formed on retina is recognized based on the earlier memory and experience.

Step 2: Match the sequence with options

After recognizing the correct sequence of events in vision, we now match this sequence with the provided options. The option which matches our sequence is: \(8,1,2,3,4,5,6,7\).

Key Concepts

Photoreceptor Cells

Photoreceptor cells are specialized neurons found in the retina of the eye. They are essential for the initial steps in the mechanism of vision, where light is converted into electrical signals. There are two main types of photoreceptor cells: rods and cones.

• Rods, which are highly sensitive to light and help us see in low-light conditions, are more numerous and found mostly in the peripheral regions of the retina.
• Cones, on the other hand, are responsible for color vision and function best in bright light conditions. They are concentrated in the fovea, a central region of the retina.

In photoreceptors, the light-induced dissociation of the retinal from opsin leads to a series of changes, culminating in potential differences. This early conversion of light signals is fundamental to visual processing, enabling us to perceive and interpret the world around us.

Bipolar Cells

Bipolar cells play a crucial intermediary role in the visual pathway. They receive input from photoreceptor cells and pass this information onto ganglion cells. This transmission process is a fascinating part of the mechanism of vision because it bridges the gap between the initial detection of light and the generation of nerve signals. When photoreceptor cells undergo changes due to light exposure, they alter the membrane potential. This modification triggers bipolar cells, which then influence ganglion cells by altering their potential as well.

• The interaction results in the creation of action potentials (AP) in ganglion cells.
• These electrical impulses are essential as they carry the visual information through the optic nerve, guiding it toward the brain for further processing.

Bipolar cells, therefore, act as critical conduits that relay and refine the visual signals essential for image formation.

Visual Cortex Analysis

Once the action potentials travel via the optic nerve, they reach the visual cortex in the brain. The visual cortex is where these electrical signals are interpreted, allowing us to "see" the image formed on the retina. The analysis process involves several complex steps: - The primary visual cortex initially processes basic attributes of the image, such as lines, colors, and movements. - As the data is further examined, higher visual areas integrate these pieces into coherent patterns and shapes, eventually forming a recognizable image. Our brain's previous experiences and memories play a vital role in this analysis. It helps the visual cortex recognize and make sense of new images based on what we've seen before. This intricate orchestration enables not only the recognition of familiar faces and objects but also the ability to learn and adapt to new visual experiences over time.

Retinal and Opsin Interaction

The interaction between retinal and opsin is at the heart of photo transduction in the eye. Opsin is a protein located in the photoreceptor cells, and its role, alongside retinal, is pivotal in the visual cycle.

• When light enters the eye, it causes the retinal, a molecule bound tightly to opsin, to change shape and dissociate from opsin.
• This structural change in opsin triggers a cascade of biochemical reactions within photoreceptor cells, altering the membrane permeability and initiating electrical signaling.

The dissociation of retinal from opsin is the primary trigger that begins the whole vision process. Without this critical interaction, the conversion of light into electrical signals within the eye would be impossible, and visual perception as we know it would not occur.