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Natural Science
NATS 1870
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PhysiologyClass 12 Anatomy of the EyeEyes are also our main tool of perception of our surroundings gathering up to 75 of our total sensory informationPupilthe black aperture opening of the eye through which light enters the eye similar to the aperture of a cameraoEverything that we see is from light that enters the eye through the pupil onlyIrisa muscle diaphragm suspended over the lens of the eye It also contains pigments that determine the colour of eyesoThe iris can shrink back on the lens enlarging the pupil or the openingpupil dilation or stretch forward over the lens reducing the pupil or the openingpupil constrictionPupil DilationConstrictionoDim Lightingthe iris will shrink back over the lens to enlarge the opening pupil dilation to allow more light to enter the eyeoBright Lightingthe iris will stretch forward over the lens to reduce the opening pupil constriction to reduce amount of light entering the eyeoOther artificial stimulants such as drugs can also induce pupil dilation andor constrictionQIt is not Pupil itself that dilate but Iris does Sclera the Whites of the Eye a dense white opaque outer shell of the eye ball except the front part over the lensiristhe transparent cornea It is made of a dense 1connective tissues filled with the protein collagen to protect the inner components of the eye as well as maintain the spherical shape of the eyeball2Cornea23 of Eyes Optical Power a transparent covering layer over the pupil and iris front of the eye with index of refraction of n1376oIt provides about 23 of the eyes total optical power ability to focus incoming light through refraction howo It serves to protect cover the lens while being transparent to light passing through it into the pupilAqueous Humortransparent fluid mostly water between the cornea and lensiris It protects the lens and cornea provides oxygen and nutrients to them and removes waste from themLensa crystalline lenslike nearlyspherical object in the eye behind the cornea and aqueous humor It provides the remaining 13 of the eyes optical power focusing the light passed through the cornea onto the retina at the back of the eye through refraction and shapedeformationoCiliary Musclessmooth muscle fibres attached to the lens that can contract in turn causing the lens to stretch out elongate This is how the lens can adjust or deform its shape and thus change focusby the ciliary muscles pulling on it to stretch it out and releasing again to let it fall back to its more round shapeVitreous Humorabout 80 of eyetransparent fluid between the lens and retina It helps to keep the spherical shape of the eye inside as well as give a clear unobstructed transparent path for the light to arrive at the retinaQThere are 4 components of eyesinvolved in 4 refraction of light 1 Cornea 2 Aqueous Humor 3 Lens and 4 Vitreous HumorQWe have a blurry vision in water because Cornea itself mostly made of water reducing the difference in indices of refraction Retinaa layer of nervous tissue covering the inner back 23 of the eyeball in which stimulation by light initiates an electrochemical reaction in which electrical impulses are transmitted to the brain producing the sensation of visionoThe main job of the eyes optics is to focus light onto the retina like onto a filmRetinaLayers of Specialized CellsRetina is the layer which contains several layers of specialized cells including the photoreceptor cells rods and cones and the pigment epithelium layer as the outermost layer of the retina right behind the photoreceptorsPhotoreceptors Rods and ConesoRods and Cones are Photoreceptors specialized neuron cells in the retina of the eyes which are capable of phototransduction conversion of absorbed light into an electrical impulse sent to the brainoThere are about 6 million cone cells in the retina of each eye used to distinguish colour in daylight and about 100 million rod cells in each lightdark vision during dim lightingoThey each contain a different type of photopigment which is made in the inner segment and then stored in the outer segment of the celloRods have the rhodopsin photopigment while each cone has an individual variation of the photopsin photopigment Each one sensitive to a different spectral range of light 3
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