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10&11_biology of seeing '09

10&11_biology of seeing '09 - The Biology of Seeing...

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1 The Biology of Seeing Recent article in Nature : color blindness in monkeys cured by gene therapy! How sensory stimuli elicit behavior • Information, in the form of energy , is – detected by sensory receptor cells. t nsmitt d b s ns n ns t – transmitted by sensory neurons to nervous system. – integrated by nervous system which activates muscles. – sequence modified by hormones Energy can be: – light – sound Corresponding sense: seeing hearing Animal Senses – mechanical – chemical – magnetic – electrical touch & proprioception smell & taste magnetoreception electroreception Seeing, or Vision Vision commonly involves assessment of: A d i i f li h A. presence and intensity of light B. color and other properties C. images D. distance, location and motion of objects A. Detecting light Light is electromagnetic radiation . Light has properties of particles, called photons . Detecting light = detecting photons
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2 Rhodopsin is a protein complex consisting of two subunits, opsin and retinal* . Opsin Detecting photons requires the photopigment molecule rhodopsin . Retinal * Genes code for these subunits! When retinal absorbs a photon, it changes shape. Light cis form trans form Opsin Retinal Rhodopsin Change in shape activates leads to the closing of closing of Na+ channels and a change in membrane’s electric change in membrane’s electric potential potential. Important! All sensory detection involves conversion of some kind of energy into bioelectrical energy . B. Seeing in Color Color provides information that brightness alone does not. Some Uses of Color in Animals courtship signals warning coloration nectar foraging
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3 What is Color? Radio Microwaves Infrared Short λ ’s Ultraviolet Gamma Long λ ’s Light also has properties of waves Color relates to wavelength ( λ ) (for humans) Wavelength sensitivity of rhodopsin depends on amino acid composition of opsin* . Opsin Retinal Rhodopsin *Different genes code for different opsins. 1.0 L opsin 560 M opsin 530 S opsin 420 Visible spectrum Human color vision involves 3 opsins. Relative proportion of light absorbed 0.8 0.6 0.4 0.2 0.0 400 500 Wavelength (nm) 600 1. Dichromatic vision – 2 pigments -- many insects, most mammals, incl. dogs 2 Trichromatic vision 3 pigments Dogs are not really colorblind! # of colors discriminated increases with # of photopigments 2. Trichromatic vision – 3 pigments -- primates (humans), bees, other insects 3. Tetrachromatic vision – 4 pigments -- birds, some butterflies 4. Dodecachromatic vision – 12 channels! -- mantis shrimp 1.0 0 8 L opsin 560 M opsin 530 S opsin 420 Human ‘color blindness’ involves an opsin deficit. Red-green blindness involves loss of M or L opsin .
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