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Eye + Retina 👁, Photoreceptors, Rhodopsin, Retina, Temporal + nasal,…
Eye + Retina
👁
Retina
Structure
Thin layer of tissue located in back of eye
Fovea = where most detailed vision is🔭
Divides retina into temporal + nasal retina➗
Overlaying layers of rods + cones
Bent to the sides to allow more light
Temporal retina = part closest to the temples
Nasal retina = part closest to the nose👃
Optic disk / Blind spot = where optic nerve exits eye + where blood vessels are found🙈
Layers of modified nerve cells🥞
Top
Ganglion cells
Axons that make up optic nerve
Light passes through easily
Have long axons🦒
Only layer of cells firing action potentials⚡️
Middle
Bipolar cells
Light passes through easily
No action potentials❌
Graded electrical potentials
Synapse w/ Ganglion cells🌉
Releasing glutamate
Bottom
Photoreceptors
Why they’re in the very back
Photopigments need to be renewed into “stack of pancakes”♻️
Bottom pigments exiting and being broken down by Pigmented Epithelium
Synapse w/ Bipolar cells🌉
Releasing glutamate
Releasing in the dark + stop releasing where there is light
No action potentials ❌
Photoreceptors
If oriented the opposite way🔀
Old photopigments would be discarded into the center of eye🗑
More “gunk” in the middle of eye🦠
Rods
More light sensitive💡
Good for low light conditions
AKA scotopic vision / night vision🌃
Larger outer segments of disks containing photopigments
More sensitivity
Cones
Less light sensitive🌈
Good for bright light condtions
AKA photopic vision
Types
“Blue”
430 nm
Sensitive to short wavelengths
“Green”
530 nm
Sensitive to medium wavelengths
“Red”
560 nm
Sensitive to long wavelengths
Phototransduction
☀️How light is converted into electrical signals⚡️
Dark Current = sodium ions coming in from cGMP ligand-gated ion channels⚫️
cGMP binds + allows sodium inside
Light breaks down cGMP💡
cGMP levels lower
Ion channels close
Dark current stops❌
Rhodopsin = photopigments in rods
Composed of opsin + retinol
Activation🎚
In dark🌑
Retinol tail bent == inactivated❌
In light🌕
Retinol tail straight == activated✅
Vitamin A produces retinol💊
Eat carrots!🥕
In rods…
High cGMP levels in the dark🌑
Light🌕
Retinol activated
Activates rhodopsin
G-Protein (Transducin) activated
Phosphodiesterase activates
Breaks down cGMP to GMP
Sodium channels closed🔒
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In cones…
Different Opsin protein, but same retinol
Changes wavelength needed to activate retinol🌈
Photoreceptors
Rhodopsin
Retina
Temporal + nasal
Layers
Phototransduction
When light comes in