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Where is the biological response from photoreceptors communicated to?
intermediate relay cells
Where is the info from intermediate relay cells sent?
retinal ganglion cells
What is the outermost layer of the eye?
sclera
What is the intermediate layer of the eye?
choroid
What is the ciliary body composed of?
muscles, ligaments, processes in a ring
What is the innermost layer of the eye and what does it contain?
retina, photoreceptors
What fluid fills the posterior chamber behind the lens?
vitreous humor (jelly-like)
What fluid fills the anterior chamber in front of the lens?
aqueous humor (watery)
Name the roles of the accessory structures of the eye
refraction, accommodation, light entry regulation, spherical aberration reduction
When does refraction occur?
when the light rays meet a change in medium density
Where is the most major site of refraction in the eye?
interface between air and cornea
What causes common refractive errors?
when the amount of refraction from accessory structures do not match the eyeball length
What causes myopia?
light rays brought into focus before they hit the retina (too much refraction)
What is another name for ‘normal eye’?
emmetropic
What causes hypermetropia?
light rays not in focus when they hit the retina (not enough refraction)
What causes astigmatism?
corneal irregularities (horizontal & vertical light rays focus on different parts of the retina)
What is accommodation?
the process of the lens adjusting its curvature to gain refractive power through contraction of ciliary muscles
Why does the iris regulate light entry?
prevent photoreceptors saturation, allow maximum light capture in dim light, reduce spherical aberration
What is spherical aberration?
outer parts of lens distorting image due to too much refraction
What are the components of the near response?
accommodation, pupils constrict, eyes converge
Why is there a blind spot?
nerve fibres leaving the eye (no photoreceptors)
How many types of rods and cones are there?
1 rod, 3 cones
Where are the light absorbing molecules located?
outer segment of receptors
Where is the transmitter located in the photoreceptors?
end of inner segment
What are the two components of the visual pigment?
chromophore 11-cis-retinal, protein opsin
What is the visual pigment in rods called?
rhodopsin
What allows colour vision?
cones having different opsin types to absorb light best at a different wavelength
Where are cones most concentrated?
at the fovea
How are rods distributed across the retina?
absent at fovea, numbers greatest beside fovea
Why do we not see blind spots in our vision?
brain interpolates
What type of receptors are visual pigments?
G protein coupled receptors (metabotropic)
Where is the binding site for visual pigments?
chromophore 11-cis-retinal
What does the molecular cascade activated by light result in?
breakdown of cyclic GMP
What is the function of cGMP?
it holds open channels that allow Na+ and Ca2+ in
Why is there a complex cascade system?
for amplification
What does light adaptation do?
allows us to cope with constant background light by producing more cGMP
Why is daytime vision dependent on cones?
rods break down cGMP faster
Why do cones signal fast events and rods slow?
recovery rate is faster in cones
What is the receptive field (RF)?
set of photoreceptors that RGC gets info from
What are the two parts of RFs?
centre (direct), surround (indirect)
Where are the smallest RFs?
fovea
What do large RFs and small RFs do?
small: high visual acuity, large: signals object presence