10
Vision I
Light
Electromagnetic radiation with wavelengths in range of 400 – 700 nm
https://upload.wikimedia.org/wikipedia/commons/f/f1/EM_spectrum.svg
Color mixing
http://www.indiana.edu/~jkmedia/classes/images/colormodes.jpg
Photoreceptive organ
Light detection
Image formation
Light detection
• Circadian activity
– Both prokaryotes and eukaryotes
– Day/night cycle is the most influential and the most stable biorhythm
Light detection
• Circadian activity
– Both prokaryotes and eukaryotes
– Day/night cycle is the most influential and the most stable biorhythm
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
• Season activity
https://upload.wikimedia.org/wikipedia/commons/thumb/3/30/Biological_clock_human.svg/2000px-Biological_clock_human.svg.png
Biological clock
• Cellular level
– Group of proteins rhythmically expressed creating interconnected
feedback loops (about 24hours)
Biological clock
• Cellular level
– Group of proteins rhythmically expressed creating interconnected
feedback loops (about 24hours)
• Tissue level
– Peripheral oscillators
– Adrenal gland, lung, liver, pancreas, skin
– Influenced by neurohumoral factors and also by light
Biological clock
• Cellular level
– Group of proteins rhythmically expressed creating interconnected
feedback loops (about 24hours)
• Tissue level
– Peripheral oscillators
– Adrenal gland, lung, liver, pancreas, skin
– Influenced by neurohumoral factors and also by light
• Central pacemaker
– Hypothalamus (nucleus suprachiasmaticus)
– Clock protein expression
– Information about illumination from retina (specialized ganglion cells)
– synchronization of central pacemaker
 Pineal gland - melatonin
 Autonomnic nervous system – adreanl gland - cortisol
http://slideplayer.com/slide/7013288/
Image formation
https://www.fotoskoda.cz/images/manufacturers/camera_obscura.png
Image formation
https://www.fotoskoda.cz/images/manufacturers/camera_obscura.png http://de.academic.ru/pictures/meyers/large/030717c.jpg
Image formation
 Shape
 Color
 Localization
 Movement
 Image interpretation
http://www.slideshare.net/CsillaEgri/presentations
Image formation
http://www.slideshare.net/drpsdeb/presentations
http://www.slideshare.net/drpsdeb/presentations
Photopigment of rods
• Opsin
– G – protein
• Retinal
– Aldehyd retinolu (vit. A)
Rhodopsin
http://www.slideshare.net/CsillaEgri/presentations
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
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
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
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
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