Explain the mechanism of vision in human eye.
The light rays emitted by various objects are captured by eyes and then send inwards. The light rays entering the eyes are either parallel or diverging when they strike the eye. In both the cases, the light rays need to be bend or refracted to focus on the retina. The work of refracting the light rays is done by curved corena. The work of refracting the light rays is done by curved cornea, refracting eye lens and the humors present in the eye. The light rays are visible wavelength are focussed on the retina through the cornea & the lens. This generates the potentials (impulses) in the rods and the cones present in the retina.
The photosensitive compounds (photopigments) in rods in the human eyes are composed of opsin and retinal. Similarly, the cone pigments in human eyes are composed of retinal and three different types of proteins (opsins) to which retinals are attached. However, when light falls on rods and cones, it causes dissociation of retinal from opsin. This results in changes in the structure of the opsin. This change in the structure of the opsin, causes membrane permeability changes. As a result, potential differences are generated in the photoreceptor cells, i.e., rods and cones. As the photoreceptor cells synapse with the bipolar cells, a signal generates the action potential in bipolar cells also. Now bipolar cells synapse with the ganglion cells, so action potentials are generated in the ganglion cells through the bipolar cells. So finally the action potential (impulses) generated in the ganglion cells are transmitted through their axons, i.e., optic nerve to the visual contex area of the brain. After reaching the visual cortex area, the neural impulses are analyzed the image formed on the retina is recognized. This recognition is based on earlier memory and the experience stored in the brain.