9 Vision I 1 Light Electromagnetic radiation with wavelengths in range of 400 – 700 nm https://upload.wikimedia.org/wikipedia/commons/f/f1/EM_spectrum.svg 2 Color mixing http://www.indiana.edu/~jkmedia/classes/images/colormodes.jpg 3 Photoreceptive organ ✓Light detection ✓Image formation 4 Light detection • Circadian activity – Both prokaryotes and eukaryotes – Day/night cycle is the most influential and the most stable biorhythm 5 Light detection • Circadian activity – Both prokaryotes and eukaryotes – Day/night cycle is the most influential and the most stable biorhythm 6 Light detection • Circadian activity – Both prokaryotes and eukaryotes – Day/night cycle is the most influential and the most stable biorhythm – Oscillation with a period of aprox. 24 hours even without signals from environment – Environmental signals synchronize circadian activity • Seasonal activity 7 https://upload.wikimedia.org/wikipedia/commons/thumb/3/30/Biological_clock_human.svg/2000px-Biological_clock_human.svg.png 8 Biological clock • Cellular level – Group of proteins rhythmically expressed creating interconnected feedback loops (about 24hours) • Peripheral Clock protein expression 9 Biological clock • Cellular level – Group of proteins rhythmically expressed creating interconnected feedback loops (about 24hours) • Peripheral Clock protein expression • Tissue level – Peripheral oscillators – Adrenal gland, lung, liver, pancreas, skin – Influenced by neurohumoral factors and also by light 10 Biological clock • Cellular level – Group of proteins rhythmically expressed creating interconnected feedback loops (about 24hours) • Peripheral Clock protein expression • Tissue level – Peripheral oscillators – Adrenal gland, lung, liver, pancreas, skin – Influenced by neurohumoral factors and also by light • Central pacemaker – Hypothalamus (nucleus suprachiasmaticus) • Central clock protein expression • Information about illumination from retina (specialized ganglion cells) – synchronization of central pacemaker ➢ Pineal gland - melatonin ➢ Autonomnic nervous system – adreanl gland - cortisol 11 http://slideplayer.com/slide/7013288/ 12 Image formation https://www.fotoskoda.cz/images/manufacturers/camera_obscura.png 13 Image formation https://www.fotoskoda.cz/images/manufacturers/camera_obscura.png http://de.academic.ru/pictures/meyers/large/030717c.jpg 14 Image formation ➢ Shape ➢ Color ➢ Localization ➢ Movement ➢ Image interpretation http://www.slideshare.net/CsillaEgri/presentations 15 Image formation http://www.slideshare.net/drpsdeb/presentations 16 http://www.slideshare.net/drpsdeb/presentations 17 Photopigment of rods • Opsin – G – protein • Retinal – Aldehyd retinolu (vit. A) Rhodopsin http://www.slideshare.net/CsillaEgri/presentations 18 Photopigments of cones • 3 types of cones - 3 types of photopigment – Blue(420nm) – Green (530nm) – Red (560nm) • Color is interpreted by ratio of cone stimulation – Orange (580nm) • Blue: 0% • Green: 42% • Red:99% Rod http://www.slideshare.net/CsillaEgri/presentations 19 Photopigments of cones • 3 types of cones - 3 types of photopigment – Blue(420nm) – Green (530nm) – Red (560nm) • Color is interpreted by ratio of cone stimulation – Orange (580nm) • Blue: 0% • Green: 42% • Red:99% Rod http://www.slideshare.net/CsillaEgri/presentations 20 Phototransduction • Photoreceptors continuously release neurotransmitter (glutamate) in darkness • In response to the light, the membrane hyperpolarizes and release less neurotransmitter http://www.slideshare.net/drpsdeb/presentations 21 Phototransduction - darkness • Guanylate cyklase – cGMP • cGMP-gated Na+ channels – Na+ influx • Voltage gated Ca2+ channels – Release of glutamate • The balance is kept by – K+ efflux – Na+/K+ exchanger • Resting membrane potential: – 40mV http://www.slideshare.net/drpsdeb/presentations 22 Phototransduction - light • Photon is absorbed by photopigment • Isomerization of retinal • Cascade of reactions result in cGMP phosphodiesterase – cGMP levels decreased • Deactivation of cGMP gated Na+ channels • K+ efflux continues • Membrane hyperpolarization – Deactivation of voltage Ca2+ channels – Decrease in glutamate release http://www.slideshare.net/drpsdeb/presentations 23 Adaptation to the light/darkness • Optic adaptation – Constriction of pupils • Photoreceptor adaptation – Ca2+ inhibits guanylate cyclase – Light • Ca2+ decreased - cGMP increased – Darkness • Ca2+ increased – cGMP decreased – cGMP gated Na+ channels... http://www.slideshare.net/drpsdeb/presentations 24