Mechanism of Vision – Class 11 | Chapter – 21 | Biology Short Notes Series PDF

Mechanism of Vision: Eye is the sense organ that is responsible for vision in animals. All the physiological components of the body responsible for vision are known as the visual system. This system is responsible for colour vision, motion perception, pattern recognition, sense of light.Humans have a pair of eyes located in cavities of the skull called orbits. The part of the eye that is visible to us comprises the cornea, sclera, iris, and pupil. The sclera is covered by a very thin layer called conjunctiva. The white visible part of the eye is called cornea – it is transparent and curved. The pupil is an aperture like structure located at the center of the iris.

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Mechanism of Vision

The posterior part of the eye comprises the lens, retina, aqueous and vitreous humour and the optical nerve.

Eye Structure

Eye contains the photoreceptor cells called rod cells and cone cells. These cells are present in the retina. Light falling on the eye is channeled to these photoreceptors by the pupil. The light energy is then converted to electrical signals and transmitted to the brain. The electric signals are interpreted as sight or vision.
The rod cells are responsible for night vision, while the cone cells for day vision or bright light vision. These cells contain a photopigment called Rhodopsin. Rhodopsin in turns comprises a protein called opsin and a light absorbing molecule called retinal.

The mechanism of vision can be explained in the following steps:

♦ Light rays in the visible spectrum are focused on the retina with the help of cornea and lens.

♦This generates an impulse that causes dissociation of rhodopsin into opsin and retinal.

♦This dissociation in response to light, causes alteration in the structure of opsin.

♦The change in opsin structure leads to changes in the permeability of membranes of the eye which lead to potential differences in the photoreceptor cells.

♦The photoreceptors are connected to the bipolar cells through synapses. The bipolar cells in turn form synapse with the ganglion cells. Therefore, potential difference generated in the photoreceptor causes the ganglion cells to generate impulses.

♦The impulses are then transmitted to the visual cortex of the brain through the optical nerve.

♦The visual cortex analyzes the impulse which enables us to recognize the image formed on the retina and results in vision.


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By Team Learning Mantras