PSIO 5th Edition Lecture 37Outline of Current Lecture I. VisionII. Origins of the eyeIII. Common defects IV. RetinaV. RhodopsinVI. Rod PhotostransductionCurrent LectureSensory Function: VisionTwo 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 round2. The entering angle of the light increases3. The light gets more refracted on the focused image now falls onto the retinaCommon 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 theaged eye cant focus on close up objects Physiology of vision – focused image is displayed o on retinaRetina – - 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 brainRhodopsin- - Consists of opsin and retinal,- Rhodopsin activation closes sodium channels- This leads to cell hyperpolarizationRod Phototransduction1. Light photon actives rhodopsin2. This activated an enzyme that breaks down cyclic GMP3. cGMP gated sodium channels close4. the rod hyperpolarized5. Glutamate release is
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