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Sensory System

Sensory System. 4-25-2016. Sensory receptors. Somatic -- Chemoreceptors (taste, smell, smell) -- Thermoreceptors (temperature) -- Photoreceptors (vision) -- Baroreceptors (sound, balance) -- Proprioreceptors (muscle stretch). Visceral

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Sensory System

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  1. Sensory System 4-25-2016

  2. Sensory receptors Somatic -- Chemoreceptors (taste, smell, smell) -- Thermoreceptors (temperature) -- Photoreceptors (vision) -- Baroreceptors (sound, balance) -- Proprioreceptors (muscle stretch) Visceral -- Chemoreceptors (chemicals in blood, osmoreceptors) -- Baroreceptors (blood pressure)

  3. Sensory transduction Receptors transform an external signal into a membrane potential Two types of receptor cells: - a nerve cell - a specialized epithelial cell

  4. Sensory pathways The sensory pathways convey the type and location of the sensory stimulus The type: because of the type of receptor activated The location: because the brain has a map of the location of each receptor

  5. Sensory coding A receptor must convey the type of information it is sending  the kind of receptor activated determined the signal recognition by the brain It must convey the intensity of the stimulus the stronger the signals, the more frequent will be the APs It must send information about the location and receptive field, characteristic of the receptor

  6. Receptor adaptation Tonic receptors -- slow acting, -- no adaptation: continue to for impulses as long as the stimulus is there (ex: proprioreceptors) Phasic receptors -- quick acting, adapt: stop firing when stimuli are constant (ex: smell)

  7. Vision Charles Darwin’s “Origin of the species” (1882) under the heading of “Difficulties of the theory”:How to explain the origins of organs ofextreme perfection, like the eyes of eagles. Darwin proposed a very simple prototypic eye consisting of just two cells, a photoreceptor cell and a pigment cell, shielding the light from one side.

  8. Protistology: How to build a microbial eye Nature 523, 166–167 (09 July 2015)

  9. http://dx.doi.org/10.7554/eLife.12620.004 Single-celled photosynthetic bacteria acting as lenses. eLife, 5, e12620: 2016

  10. Hou XG, et al. 2007. The Cambrian fossils of Chengjiang (澄江) China, the flowering of early animal life. Oxford: Blackwell

  11. Pax 6 is a master control gene for eye development

  12. Chance and Necessity in Eye Evolution Genome Biol. Evol. 3:1053–1066.; 2011

  13. Retina Human eye DRAWING FROM: Gillian Lee, Wellcome Images.

  14. Retina Is our eye a perfect design?

  15. Onerhodopsin molecule Absorbs one photon 500 Transducin molecules are activated 500Phospodiesterase molecules are activated 105 cGMP molecules are hydrolyzed 250Na+ channels closed 106-107ions/sec are prevented from entering the cell for a period of 1 sec Rod cell membrane is hyperpolarized by 1 mV

  16. Termination of receptor activation Science, 297, 529 (2002)

  17. Classe of light receptor in human • Cone photoreceptors: • 440nm; • 530nm; • 560 nm. • Rod photoreceptors: 500 nm. • Retinal ganglion cells: 480 nm.

  18. Cone cells carry three different opsins for color dection (with same retinal) Rod cells carry opsin for black/white light dection

  19. LWS opsin 277 Phenylalanine N Outside cell Membrane C Inside cell 285 Alanine 180 Alanine

  20. MWS opsin 277 Tyrosine N Outside cell Membrane C Inside cell 285 Threonine 180 Serine

  21. 1.0 SWS MWS LWS 0.8 0.6 Absorbance 0.4 0.2 0.0 400 450 500 550 600 650 700 Wavelength (nm) DATA FROM: Stockman, et al, 1993.

  22. Convergence

  23. The rods’ greater spatial summation enables them to cause ganglion cell firing at lower stimulus intensities than the cones’.

  24. Rods do not pick up on location. Cones pick up on location. • One-to-one wiring leads to ability to discriminate details • Trade-off is that cones need more light to respond than rods

  25. Evolution of trichromatic vision

  26. The Evolution of Primate Color Vision by Gerald H. Jacobs and Jeremy Nathans Scientific American April 2009 page 60

  27. The Evolution of Primate Color Vision by Gerald H. Jacobs and Jeremy Nathans Scientific American April 2009 page 61

  28. The Evolution of Primate Color Vision by Gerald H. Jacobs and Jeremy Nathans Scientific American April 2009 page 62

  29. The Evolution of Primate Color Vision by Gerald H. Jacobs and Jeremy Nathans Scientific American April 2009 page 62

  30. Color Vision Deficiency “Color Blindness” • Color-blind humans have dichromatic vision and can distinguish short-wavelength stimuli (blue) from long-wavelength stimuli (not blue). • Introduction of photopigment genes into animals with dichromatic vision to make them become trichromatic. • We may be able to correct dichromatic vision in humans. • What other message you get from that observation?

  31. “Real taste [in] the mouth, in my theory must be acquired by certain foods being habitual—[and] hence become hereditary” Charles Darwin’s Notebooks, 1836–1844

  32. Distribution of taste receptors on the tongue Bitter Salt Sweet Umami Sour AFTER: Chandrashekar, J. et al. (2006) Nature444: 288.

  33. Bitter Salt Sweet Umami Sour Each taste bud is thought to contain all types of receptor AFTER: Chandrashekar, J. et al. (2006) Nature444: 288.

  34. Taste receptors

  35. Bitter T2R protein Sweet T1R2 + T1R3 protein T1R2 T1R3 Umami T1R1 + T1R3 protein IMAGES FROM: Dean Madden. T1R1 T1R3

  36. New virus leaves cell HIV attaches to CD4 receptors on T-Cell 6 1 2 3 4 5 Human 1 2 3 4 5 6 Panda Mutations in exons 3 and 6 1 2 3 4 5 6 Umami receptor gene Dog PHOTO BY: J. Patrick Fischer, Wikimedia Commons.

  37. Other examples • For whales, mammals that migrated back to the sea from land 25 to 55 million years ago, extensive losses of sweet, umami, bitter, and sour tastes were found. • Genome Biol Evol. 2014 Jun; 6(6): 1254–1265.

  38. "the umami and bitter tastes were lost in the common ancestor of all penguins, whereas the sweet taste was lost earlier" Molecular evidence for the loss of three basic tastes in penguins Current Biology 25, pR141–R142, 2015 Make an explanation!

  39. Dynamic changes of sweet loss of the sweet taste receptor gene Tas1r2 in many obligate carnivores. all birds also have lost the Tas1r2 taste receptor gene! How can one explain the appetitive behavior of bird species such as hummingbirds that typically consume foods that consist primarily of sweet sugars?

  40. Science 8/22/2014 Page 878-9

  41. Signal transduction from the olfactory GPCRs.

  42. Structures of olfactory receptor neurons.

  43. The anatomy of olfaction in the mouse.

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