Module 14 - mammalian eye Flashcards
What does amplitude and wavelength show respectively
intensity of light and colour of light
what nm range is visible light
380-750 nm
diff between cornea and lens in terms of refractive power
cornea is 42D
And lens is 12D
But lens can adjust its shape unlike the cornea
Fun toon of aqueous and vitreous humours
fluid filled areas
Allow light through and keep structure of eye
What 2 things hold lens in place
zonule fibres
Ciliary musxlea
What type of lens needed when looking at something far and close respecfively
Flat and fat
Name of short and long sightedness
myopia
Hyperopia
What type of lens corrects myopia and hyperopia
myopia = concavw
Hyperopia = convex
what does light path have to cross first to get to rods and cones
retinal ganglion cells
amacrine cells (lateral)
bipolar cells
horizontal cells (also lateral)
then gets to cones and rods
(remember information pathway back to brain is the opposite way)
what does the retinal pigment epithelium do
layer at very back behind rods and cones
- makes pupil look black
-recycles retinaldehyde
- helps rods and cones deal with oxidative stress
where is max visual acuity
fovea
where most cones are
this is blind at night
what is opsin
GPCR w/ 7 TM domains
5 diff types (3 cones, a rod type, and melanopsin)
what is opsin bound to
retinal (cis when it’s dark, trans when light)
cGMP effect on vision
DARK - cGMP present in photoreceptor
opens Na+ channels = depolarised
glutamate released
LIGHT - cGMP broken down to GMP
Na+ channels closed = hyperpolarised
no glutamate released
what molecule needs to be activated for cGMP to be broken down
phosphodiesterase
phototransduction
Light = cis retinal —> trans retinal
GDP to GTP in transducin
Gprotein dissociates from rhodopsin
and activates PDE
causing cGMP to GMP
how many cones do humans have
3 cones - trichromats
RGB
allow colour perception
how many cones in most aquatic animals
1
monochromats
examples of dichromat animals
dog
reptile
mice
kitty
hors
what type of animals cones have most complicated visual system
mantis shrimp
12-16 cone types
use it for communication
why men more likely to be colour blind
red and green opsin on X chromosome
and they only have 1
(mostly red green colour blindness)
how can some women be tertrachromats
might have 2 red alleles, 1 on each X chrom
usually 1 should get inactivated, but sometimes doesnt and so higher capacity to discriminate colours
what chromosome is blue opsin on
chrom 7
what are the 2 types of bipolar cells
OFF = bipolar cell is hyperpolarised
ON = bipolar cell is depolarised
(both respond to photoreceptor being hyper or de polarised)
functions of horizontal cells
adapting eye to light intensity
spatial and colour processing
functions of amacrine cells
directional motion
modulate light adaptation
and therefore circadian rythm
and sensitivity of night vision
function of retinal ganglion cells
colour, motion, shape processing
fire APs after recieivng signals from bipolar cells
what are ipRGC
they are phtosensitive cuz they have melanopsin
so can detect light intensity
function of melanopsin
detects light intensity
- circadian rhythms
- pupil size
-body temp
what part of retina crosses to other side of brain, and what part stays on same side of brain
nasal retina - crosses over
temporal retina - stays on same side
part of breain that are primary target of retinal gnaglion cells
lateral geniculate nucleus (LGN)
where is primary visual cortex
occipital lobe
(aka V1)
how does orietnation selectivity work in V1
APs fired differ depending on orientation of visual stimuli
