Lecture 9 - Vision Flashcards
Sensation
Cells of nervous system detect stimuli in environ. (Light, sound, heat…)
-> transduce signals into change in membrane potential & NT release
Perception
Conscious experience & interpretation of sensory info
Sensory neurons (Sensory receptors)
Specialized neurons: Detect specific category of physical events
Receptor proteins: sensitive to specific sensory stimuli, specific features of extracellular environ.
Sensory receptors sensitive to:
1) Presence of specific molecules (via chem interactions)
-smell, taste, nausea, pain
2) Physical Pressure
-touch, stretch, vibration, acceleration, gravity, balance, hearing, thirst, pain
3) Temperature
-heat, cold, pain
4) pH (acidity, basicity)
-sour taste, suffocation, pain
5) Electromagnetic radiation (light)
-vision
Some non-human animals - other senses
Ability to detect electrical & magnetic fields, humidity, water pressure
Sensory transduction
NT release when there’s no action potential:
Some sensory neurons not have axons or action potential, all release NT
Small cells: release NT in graded fashion, depending on membrane potential
->More depolarized, More NT released
Neural Transduction of Light (Opsins)
Opsins: Receptor proteins sensitive to light
-> 4 diff types of opsins to detect light
4 Opsin proteins for Vision
1) Rhodopsin
2) Red cone opsin
3) Green cone opsin
4) Blue cone opsin
Each photoreceptor cell in eye contain only 1 of these opsins, so 4 diff types of photoreceptor cells
4 Photoreceptor cells (express 4 opsins)
1) Rod cells -> rhodopsin
2) Red cone cells -> red cone opsin
3) Green cone cells -> green cone opsin
4) Blue cone cells -> blue cone opsin
2 Configurations of retinal
See pic
Visible light
Electromagnetic energy with wavelength between 380 & 760 nm (detect with 4 photoreceptor cells)
See pic
Rod cells (1 kind)
Very sensitive to all visible light
(See pic)
Cone cells (3 kinds)
Not particularly sensitive to light
3 kinds: each sensitive to diff wavelengths -> encode colour vision
(See pic)
Trichromatic Coding (cone photoreceptors)
3 cone opsins sensitive to diff wavelengths of light
1) Blue cone opsins: short wavelengths
2) Green cone opsins: medium wavelengths
3) Red cone opsins: long wavelengths
Colour perception
Function of relative rates of activity in 3 types of cone cells
(colour discriminated by ratio of activity across 3)
(See graph pic)
Activation of cone cell
Depends on:
1) Wavelength of light
2) Intensity (amount) of light
Green opsin most sensitive to light, so green colour light shines brightest out of three at same intensity
(See 2 pics)
Additive vs Subtractive Color: Light vs Paint
See pic
Perceptual Dimensions of Colour & Light
3 dimensions:
1) Brightness - Intensity (luminance, amount)
2) Saturation - Purity (composite wavelengths)
3) Hue - Dominant wavelength (colour)
(See pic)
If Brightness 0%
Image is Black
Hue & Saturation have no impact
If Saturation 0%
Image is Black & White, cuz
Middle of colour cone, where no colour (equal contribution from all wavelengths)
Colour vision deficiency
1) Protanopia (no red cone)
2) Deuteranopia (no green cone)
3) Tritanopia (no blue cone)
(See pic)
Achromatopsia: True colour blindness (mutations in G protein signaling cascade) -signaling cascade similar in all cone cells
Cornea
Outer, front layer of eye
-Focuses incoming light a fixed amount
Iris
Pigmented ring of muscles
Lens
Several transparent layers
