The Vision ThingThe Doors of Perception: Cell SensorsA case study in light, vision and evolutionStructure of the vertebrate eyeDifferent eye designs: An amazing story of evolutionCambrian explosion and eyesErbenochile erbeniCurrent thinking on Why vision in the visible part of the spectrumCells in the retina (note poor design)Cells of the retinaRods and cones in the retinaDifferent photoreceptors: A living record of evolutionDifferent photoreceptors: evolutionary arguments of EakinRod outer segment structureRod outer segment discs contain rhodopsinLight-induced isomerization of retinal triggers protein conformational changeEnergetics of retinal isomerization and photonsAn aside about color vision…RECap: How light leads to an electrical responseKey features of signal transduction in a rod cellActivated rhodopsin triggers a signal transduction cascadeReminder on Ion Distribution and Transport in CellsIon Channels and Transient PermeabilityMwc models of ligand-gated channelsLight-induced hyperpolarization of the rod cell membraneElectrical consequences of illuminationSynapse diffusionOther examples of synaptic communicationMeasuring individual photoreceptorsBaylor’s beautiful single photon experimentsDark noise in isolated rod cells due to thermal isomerization of retinalShutting off the signalCalcium signaling helps reset cGMP levelSeveral mechanisms for adaptationHow many photons can be PERCEIVED?Engineering mice to see redSlide 37Eyes and diffractionThe fly’s eyeThe VisionThingCourtesy of Julie TheriotThe Doors of Perception: Cell SensorsHEARING:Hair cellsVISION:Rod and cone cells(photoreceptors)TOUCH:Pacinian corpuscle (example)SMELL and TASTE:Receptor cells, one molecular receptor type per cellA case study in light, vision and evolutionAllele substitution at a color locus alters pollinator behavior. (A) Wild-type M. lewisii. (B) M. lewisii with the yellow pigment-producing YUP allele from M. cardinalis. (C) Wild-type M. cardinalis. (D) M. cardinalis withthe inactivated YUP allele from M. lewisii. The relative preference of the two pollinators, bees and hummingbirds, for each flower are indicated below. A visit by a black bear to the observation area in California reduced the size of the data set. (Adapted from H.D. Bradshaw Jr. and D. W. Schemske, 2003, Nature 426:176-178.)Structure of the vertebrate eyeImage is initially inverted on the retinaVisual cortex receives signals from both eyesLeft and right halves of the visual field are split in the brainDifferent eye designs: An amazing story of evolutionhttp://www.karger.com/gazette/64/fernald/art_1_2.htmThe likely evolution of single-chambered eyes.Arrows indicate functional developments, notspecific evolutionary pathways. (a) Pit eye,common throughout the lower phyla.(b) Pinhole of Haliotis or Nautilus. (c) Eyewith a lens. (d) Eye with homogeneous lens,showing failure to focus. (e) Eye with lenshaving a gradient of refractive index.(f) Multiple lens eye of male Pontella. (g) Two lenseye of Copilia; solid arrow shows imageposition, open arrows show movement of thesecond lens. (h) Terrestrial eye of Homosapiens with cornea and lens. Ic, imageformed by cornea alone; Ir, final image on theretina. (i) Mirror eye of the scallop Pecten.From [2].“Eyes exist in a variety of shapes, sizes, optical designs and locations on the body, but they all provide similar information about wavelength and intensity of light to their owners. Different tissues have been recruited to build lenses and retinas across the phyla. In contrast, all eyes share the same mechanism of absorbing photons, i.e. the opsin-chromophore combination has been conserved across phylogeny.”Cambrian explosion and eyes How long have eyes been around? One of the great events in the history of life is the so-called Cambrian explosion, 500+ Mya. Amazingly, there are fossils that preserve a record of insect eyes.Erbenochile erbeniCurrent thinking on Why vision in the visible part of the spectrumhttp://www.karger.com/gazette/64/fernald/art_1_2.htmAttenuation (dB/m) of electromagnetic (EM) radiation in sea water plotted as a function of frequency (Hz) and wavelength (nm) of that radiation. The narrow band of electromagnetic energy which corresponds to visible light is shown, as are the bands used for radio and television transmission. The band of EM radiation we now consider visible light is transmitted through water with an attenuation 6 orders of magnitude less than that of adjacent wavelengths. Redrawn from Fernald [1].Cells in the retina (note poor design)http://webvision.med.utah.eduSantiago Ramon y CajalCells of the retinahttp://www.bem.fi/book/28/28.htmRods and cones in the retinaSalamanderPrimateRod Outer Segments Mouse Primate SalamanderLength (µm) 24 25 22Diameter (µm) 1.4 2 11Volume (µm3) 36 40 2000Fu & Yau, 2007, Pflugers Arch. 454:805http://hubel.med.harvard.eduDifferent photoreceptors: A living record of evolutionDifferent photoreceptors: evolutionary arguments of EakinRod outer segment structureDowling, 1967 – see his book “The Retina”Rod outer segment discs contain rhodopsin~50% of disc membrane is rhodopsin~1000-2000 discs per rod outer segment~8 x 104 rhodopsin molecules per disc~108 rhodopsin molecules per rodEach rhodopsin carries one retinal“Visual purple”Light-induced isomerization of retinal triggers protein conformational changeEnergetics of retinal isomerization and photons E = h= hc/h = 6 x 10-34 J sAt 500 nm, E ~ 100 kTNote cones use the same prosthetic group (retinal) but slightly different opsin proteins shift the spectrumNathans et al., 1986, Science 232:193An aside about color vision…Humans: minor variations in the proteinMantis shrimp: four additional UV-sensitive photoreceptors (including filtering for narrow bands)Marshall & Oberwinkler, 1999, Nature 401:873Nathans et al., 1986, Science 232:193RECap: How light leads to an electrical responsehttp://faculty.pasadena.edu/dkwon/chap10_C/chap%2010%20part%20C_files/textmostly/slide16.htmlKey features of signal transduction in a rod cell http://www.easternbiotech.com/Cell-to-Cell%20Interactions.phphttp://webvision.med.utah.edu/imageswv/FuTable%203.jpgActivated rhodopsin triggers a signal transduction cascadeReminder on Ion Distribution and Transport in CellsCells (eukaryotes) divided into a number of membrane-bound compartments.Concentrations in different compartments can be orders of magnitude different.Proteins (ion channels, transporters) mediate these
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