PSIO 5th Edition Lecture 37 Outline of Current Lecture I Vision II Origins of the eye III Common defects IV Retina V Rhodopsin VI Rod Photostransduction Current Lecture Sensory Function Vision Two critical issues associated with the special sense of vision 1 How an image is formed and displayed on the sensory surface of the eye 2 How is the stimulus of a photon striking the sensory surface transduced into an electrical event Origins of the eye Light rays arrive from an object focused onto sensory of the eye retina focusing involved bending of light rays refraction refraction occurs when light passes from one medium into another Change of lends shape called accommodation 1 The lens becomes more round 2 The entering angle of the light increases 3 The light gets more refracted on the focused image now falls onto the retina Common Defects As lens ages it loses elasticity failure to round UP means the image of close up objects cannot be focused on the retina loss of this ability to accommodate means the aged eye cant focus on close up objects Physiology of vision focused image is displayed o on retina Retina Several cell layers Photoreceptors layer has 2 cell types rods and cones Rods are mono chromatic and very sensitive Cones are for color vision and not that sensitive used for brighter light Neuron layers process the photoreceptor Ganglion cells carry the signal to the brain Rhodopsin Consists of opsin and retinal Rhodopsin activation closes sodium channels This leads to cell hyperpolarization Rod Phototransduction 1 2 3 4 5 Light photon actives rhodopsin This activated an enzyme that breaks down cyclic GMP cGMP gated sodium channels close the rod hyperpolarized Glutamate release is reduced
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