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PSY280H1 (40)
Chapter 3

Ch3 Textbook Notes

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Christine Burton

CHAPTER 3 INTRODUCTION TO VISIONFocusing Light onto the Retina Light The Stimulus for Vision vision is based on visible light a band of energy within the electromagnetic spectrum a continuum of electromagnetic energy produced by electric charges and is radiated as waveswavelength the distance between the peaks of the electromagnetic wavesvisible light ranges from 400700 nanometres nmlight can also be described as consisting of small packets of energy called photonsThe Eyelight reflected from objects enters the eye through the pupil it is focused by the cornea and lens to form sharp images of the objects on the retina which contains the receptors for visionrods visual receptors that contain lightsensitive chemicals called visual pigmentssignals converge and travel to the brain via the optic nerveLight is Focused by the Eyecornea the transparent covering of the front of the eye accounts for 80 of the eyes focusing power fixed so cannot adjust focuslens 20changes its shape to adjust the eyes focusaccommodation ciliary muscles at the front of the eye tighten to increase the curvature of the lens so that it gets thicker bending lights rays to focus image of far away objectsnear point the distance at which your lens can no longer adjust to bring close objects into focusincreases as a person gets older presbyopia occurs because lens hardens with age and the ciliary muscles become weakermyopia or nearsightedness an inability to see distant objects clearlyrefractive myopia cornea andor lens bends the light too muchaxial myopia the eyeball is too longfar point the distance at which an object becomes focused on the retinahyperopia or farsightedness inability to see nearby objects clearlyusually occurs because the eyeball is too shortTransforming Light into Electricity The Visual Receptors and Transduction transduction is carried out by receptors for vision are rods and coneskey part of the rod for transduction is the outer segmentcontains stacks of discs each disc contains thousands of visual pigment moleculesthe molecule is a long strand of protein called opsin which loops back and forth across the disc membrane 7 times p48retinal only one in each visual pigment molecule it is sensitive to lighttransduction is triggered when the retinal absorbs one photon of light p48
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