Visual System I Flashcards
Iris
smooth muscle controls size of pupil
Lens
focuses image onto retina
Sclera
white part, thick membrane that holds the whole eye together
Emmetropia vs myopia vs hyperopia
Emmetropia: normal vision
Myopia: nearsightedness
Hyperopia: farsightedness
____________ contracts to reduce tension in zonule fibers, which allows the lens to (increase/decrease?) curvature
Ciliary muscle contracts to reduce tension in zonule fibers, which allows the lens to (INCREASE) curvature
What is an unaccomodated lens optimal for viewing? Describe the shape of the lens.
Optimal for viewing distant objects, the lens is thin and flat
What is an accomodated lens optimal for viewing? Describe the shape of the lens.
Optimal for viewing near objects, the lens is rounded to increase refractive power
Does accomodation range increase or decrease with age and why?
It decreases with age as smooth muscle gets stretched out, so the muscles that control the size of the pupil get weaker and weaker
_________ is a hole in the retina, a blind spot. Through this hole is where the blood vessels travel, and the axons of the neurons on the retina exit here to the brain
optic disk
What is the fovea?
What is the visual accuity like there?
Fovea is a little divot, in the center a straight line through the lens and the pupil
- Highest visual accuity, where you see the best. You cant read for example if the fovea isnt on the letters youre reading
What is unique about the structure of the fovea?
The neural elements are displaced to allow light rays direct access to photoreceptors, which contributes to its high acuity.
In the dark, photoreceptors are relatively (polarized/depolarized) and (release/do not release) transmitter onto second order neurons (bipolar cells)
In the dark, photoreceptors are relatively DEPOLARIZED and RELEASE transmitter onto second order neurons (bipolar cells)
Explain the difference in release of transmitter in the dark vs the light.
In the dark, photoreceptors are already releasing transmitter onto the bipolar cells
When light hits them, it hits the photopigment and hyperpolarizes them, releasing less transmitter onto bipolar cells
Light energy hits photopigment triggering a photochemical reaction leading to a _________ which alters transmitter release onto second order neurons (bipolar cells)
HYPERPOLARIZATION
Photoreceptors are (polarized/depolarized/hyperpolarized) in the dark.
Light leads to (polarization/depolarization/hyperpolarization)
Photoreceptors are depolarized in the dark.
Light leads to hyperpolarization.
Describe the activity of cGMP in the dark/light in retina receptors.
In total darkness:
Cyclic GMP is abundant in outer segment of photoreceptor, this leads to the opening of cation channels (sodium comes, in potassium out)
- the receptor is depolarized
With light:
Reduction of cyclic GMP around the photoreceptor, leads to closing of cation channels, and photoreceptor gets hyperpolarized. Releases less neurotransmitter onto bipolar cells
Big delay in visual system from when something happens in real world until when photoreceptors are signalling to bipolar cells (20 ms) because sequestering of GMP takes a while
Why is there a big delay in the visual system from when something happens until when the photoreceptors are signalling bipolar cells?
Big delay in visual system from when something happens in real world until when photoreceptors are signalling to bipolar cells (20 ms) because sequestering of GMP takes a while
Describe the composition of rods/cones in the retina.
In the fovea, there is more cones compared to around it, where there is less
Which photoreceptors give you high acuity vision?
Cones, most abundant in fovea
Rods ____________ in bright light. Cones ___________ in bright light.
a) saturate
b) do not saturate
Choose the correct option for both
Rods SATURATE in bright light. Cones DO NOT SATURATE in bright light.
Which one has a “many to one ratio” and which one has a “one to one” ratio with bipolar cells?
Rods/cones
Rods: many to one
Cones: one to one
Which one has a larger receptive field:
rods/cones
Rods because they have many rods to one bipolar cell
Cones only have one cone to one bipolar cell, therefore the receptive field is very small
Which one has higher acuity?
rods/cones
cones
Difference between functions of rods/cones
Rods:
- 120 to 130 million
- high sensitivity, specialized for night vision (scotopic). Saturate easily
- achromatic
- low acuity
Cones:
- 6 to 7 million
- lower sensitivty, specialized for day vision (photopic). saturate only in intense light
- critical for colour vision
- high acuity in fovea
What does it mean when something “saturates easily”
Saturate easily means when we go to bright light theyre pretty much useless
