Vision - Vision u Structure of the eye: invertebrates vs...

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Unformatted text preview: Vision u Structure of the eye: invertebrates vs vertebrates. u Structure of the vertebrate retina: rods vs cones. u Evolution of opsin genes: Compound eyes of arthropods (insects, crustacea, etc). Hooke, 1665 http://www.uky.edu/OtherOrgs/KPS/images/glyptamboneye.jpg fly trilobite The basic unit of the arthropod eye is the ommatidium, with 8 photoreceptors. http://neurophilosophy.files.wordpress.com/2006/10/431.JPG?w=581&h=396 http://scien.stanford.edu/class/psych221/projects/02/ksykang/butterfly2a.jpg Cross-section through a fly retina with 8 photoreceptors labeled. Bees see in the UV (short wavelength), and less in the red (long wavelength) end of the spectrum http://www.um.u-tokyo.ac.jp/publish_db/Bulletin/ no39/39img/39plate03.jpg visible light UV light Many flowers have distinct patterns that reflect UV light to attract pollinating insects such as bees. On the right are photographs of flowers taken with a regular camera lens (left) and a quartz lens that passes UV light (right). Some arthropods can detect polarized light by the organization of the rhabdomes in their ommatidia. http://cas.bellarmine.edu/tietjen/Laboratories/Eye02.gif Mantis shrimp have complex eyes with 8 photopigments http://blogs.nature.com/news/thegreatbeyond/shrimpy.jpg http://www.webexhibits.org/causesofcolor/images/content/mantisshrimpeyes.jpg The eye of the mantis shrimp is a marvel of evolutionary engineering. The first four rows of the middle band of photoreceptors has 8 different photoreceptor types each with a different opsin. This allows mantis shrimps to see from the infrared to the ultraviolet, the fifth and sixth rows are tuned to polarized light. Each of the three rows of photoreceptors (DH, MB, VH) have photoreceptors that focus on the same point in space (illustrated here by the dark patches) so this animal has trinocular vision. Chiou et al., 2008 Mantis shrimp also have deadly fast claws http://www.youtube.com/watch? v=mu6yrC6bjNo&feature=player_embedde d#at=52 Cephalopod molluscs also have an image forming eye with a retina much like ours. http://chemistry.csudh.edu/faculty/jim/cozaugo4-600/octopus.jpg Human octopus Vertebrate eyes Rods, which work under low light levels, are larger in diameter and packed with rhodopsin to absorb as much light as possible. They are only sensitive to one wavelength of light because at low light levels, it is more important to sum all of the available quanta for sensitivity. http://thebrain.mcgill.ca/flash/a/a_02/a_02_m/a_02_m_vis/a_02_m_vis_1a.jpg Cones are small and slender for better image formation (smaller pixel size) and since they work in high light levels, they do not need such large amounts of photopigment. Also, because the light levels are so high, they can afford to selectively absorb light at particular wavelengths to get information on color....
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Vision - Vision u Structure of the eye: invertebrates vs...

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