Explanation

Steps of Vision Light energy causes change in the shape of rhodopsin, leading to dissociation of retinal from opsin. Structure of opsin changes. Membrane permeability changes. Potential differences are generated in photoreceptor cells. Bipolar cells are depolarized. Ganglion cells are excited. Action potential (impulse) are transmitted by optic nerves in visual cortex. Neural impulses are analysed and image formed on ratina is recognised by visual cortex. Mechanism of Vision The light rays passes through cornea, aqueous humour, lens and vitreous humour and focusses on retina where they generate potential (impulses) in rods and cones. The photosensitive compound (photopigments) in the human eyes is composed of opsin (a protein) and retinal (an aldehyde of vitamin-A). Light induces dissociation of retinal from opsin which changes the structure of the opsin. Thus, potential differences are generated in the photoreceptor cells. This causes action potentials in the ganglion cells through the bipolar cells. These action potentials (impulses) are transmitted by the optic nerves to the visual cortex area in the occipital lobe of the cerebral hemisphere of the brain where the neural impulses are analysed and erect image is recognised