Vision 1 - von Bartheld Flashcards
Where is the focal point of a convex lenz?
in front of it
Where is the focal point of a concave (diverging) lens?
behind it
What is known as the distance of the focal point to the lens?
Focal length
What is the basic unit of focal power?
diopter
what is the relation between diopters and focal length?
D= 1/f
How do we determine focal power?
Focal power = Refractive index/ Focal length
Glaucoma is caused by a problem with (blank)
Aqueous humor drainage
the curvature of the (blank) controls accommodation
lens
Is the accommodated lens for flat or more round?
more round
What nucleus in the brainstem is activated during accommodation?
Edinger-Westphal nucleus of oculomotor
what ganglion is activated during accomodation?
ciliary ganglion
Ciliary muscles (relax/contract) to cause the zonule fibers to relax
contract
What structure is responsible for refractive power?
the ANTERIOR curvature of the cornea
can we adjust the curvature of the cornea?
NO
can we adjust the curvature of the lens?
why, of course!
Presbyopia is the phenomenon of:
loss of accommodation with age
Myopia is more commonly known as;
nearsightedness
hyperopia is more commonly known as:
farsigthedness
myopia is a condition in which your eye is too (long/short) for your lens focal length?
long
hyperopia is a condition in which your eye is too (long/short) for your lens focal length?
short
What type of lens do you use to correct myopia?
concave (diverging) lens
what type of lens do you use to correct hyperopia?
convex lens
What is an astigmatism?
blurry vision due to irregular curvature of the cornea or lens–can be football shaped
The blind spot is the (blank), where there are no cones or rods
optic disc
What are the five cell types found in the retina?
- Cones and rods
- Bipolar cell
- Horizontal cell
- Amacrine cell
- Ganglion cell
the cones and rods are the (deepest/most superficial) layer (as in closest to the light?
deepest
in what layer are the horizontal cells?
outer plexiform layer
are horizontal cells pre or post synaptic between bipolar cells and cones/rods?
presynaptic
are amacrine cells pre or post synaptic between bipolar cells and ganglion cells
postsynaptic
in what layer are the amacrine cells?
inner plexiform layer
what is the general function of the amacrine and horizontal cells?
transmit information laterally to adjacent ganglion cells from adjacent rods/cones
Ganglion cells send their axons to converge at the (blank)
optic disc
Does the fovea have a high concentration of rods or cones?
cones
Where are there a large concentration of rods?
On the peripheral edges of globe, farthest away from the fovea
Does the fovea receive direct blood flow?
NO, it is avascular!!
In what range of luminance do we have the best acuity?
Photopic
At what range do we reach cone threshold for sight?
Mesopic zone
At what range do we reach the absolute threshold for vision?
Scotopic
At what range does rod saturation begin?
Photopic
Is is more debilitating to lose all of your rods or cones?
cones!
What are the three reasons that cones and rods are found closest to the pigment epithelium and not closest to the light source?
- Photoreceptor discs must be regenerated every 12 days
- Photopigments must be recycled continuously
- Being deep puts them closest to the blood supply from the choroid
What is the numerical relationship between bipolar cells and rods?
1 bipolar cell to 15-30 rods
What is the numerical relationship between bipolar cells and cones?
1 bipolar cell to one cone
do have rods have a higher sensitivity or acuity? what does this make them good for?
Sensitivity
night vision
do have cones have a higher sensitivity or acuity? what does this make them good for?
acuity
high resolution vision
Describe the membrane potential of a rod after being exposed to a flash of light?
They hyperpolarize and take longer to respond to the next stimulus than cones
Describe the membrane potential of a cone after being exposed to a flash of light?
They hyperpolarize, and can quickly respond to another stimuli
In the dark, a photoreceptor is (hyperpolarized/depolarized)
depolarized
Shining a light on a photoreceptor leads to membrane (blank)
hyperpolarization
Do photoreceptors fire AP’s?
No, light causes a GRADED CHANGE in membrane potential that is correlated to the INTENSITY of the light source
Transmitter release from the synaptic terminals of the photreceptor is dependent on voltage gated (blank) ion channels
Calcium!
the number of calcium channels open when the photoreceptor is in the dark is (high/low)
HIGH
Na and Ca flow (in/out) from the photoreceptor when it is dark
IN
K flows (in/out) from the photoreceptor when it is dark
OUT
the Na/Ca channels are gated by what second messenger molecule?
cGMP
Absorption of light by the photoreceptor (reduces/increases) the conc’n of cGMP
REDUCES, which CLOSES the channels
What is the effect of closing the Na/Ca channels on the membrane potential?
HYPERpolarization
What is the photopigment of rods?
Rhodopsin
What chemical does rhodopsin contain that is the light-absorbing chromophore?
Retinal
What happens to retinal when it is exposed to light?
11-cis-retinal to all-trans-retinal
Activation of rhodopsin with a photon activates what protein?
Transducin
Transducin activates what enzyme?
phosphodiesterase
What is the purpose of the phosphodiesterase during light stimulation?
It breaks down cGMP, closing the Ca/Na channels
In the retinoid recycling process, all-trans retinAL is converted to?
all-trans-retinOL
What is the protein that transports trans-retinol into the pigment epithelium?
IRBP
Describe the series of transformations that all-trans-retinol undergoes in the pigment epithelium?
trans-retinol -> trans retinyl ester -> 11 cis retinol -> 11 cis retinAL -> bound to IRBP and transported back into the rod
Low concentrations of Ca in the (outer/inner) segment of the rod increase the activity of which two enzymes? What does this cause?
outer
guanylate cyclase
rhodopsin kinase
increased Ca/Na channel affinity for cGMP ultimately reducing the impact of light induced reductions of cGMP levels -> leading to light adaptation
Light induced closure of Ca/Na channels effects internal Ca concentration how?
It reduces internal calcium concentration
Reduced internal calcium leading to decreased calcium mediated inhibtion effects photon sensitivity how?
Photon sensitivity is reduced
do cones or rods adapt more quickly to the dark?
Cones
Do cones or rods show a greater sensitivity in the dark?
Rods by about 100x
How many pigments do cones have?
3
How many pigments do rods have
1
What are the three pigments in cones?
Short (blue), medium (green), long (red)
color pigment genes are on what chromosome?
X chromosome
Which two pigments lie adjacent to each other? What does this tell us about color blindness?
Red and green; it explains why red-green is the most common and more common in males
A dichromat is someone who…
only has two types of cones, usually with a red-green hybrid or no green at all
There is high sequence homology between which two cones?
Green and red
Protanopia is color blindness which is missing which cone?
Red
Deuteranopia is color blindness missing which cone
Green
When light is shone in the receptive field of on-center ganglia, what happens?
They fire a burst of APs
When a dark spot is left in the center of a receptive field, what do the off-center ganglia do?
They fire a burst of AP’s while the on-center ganglia are inactive
Light in the center and the surrounding ring of of the receptive field causes on and off center ganglia to do what?
Both on and off center fire several AP’s, but not as many as just the on-centers during a center-only light stimulation
Perception of light intensity is dependent on (blank and blank)
context and background
The closer the light to the center of a receptive field, the more (blank) per second from the on-center ganglia
impulses
the on-center ganglia that would have the highest level of spontaneous activity would lie where on a light-dark interface?
On the actual edge/interface between the light and dark areas
Why is it that on-center ganglia will have higher activity if they are on a light-dark edge?
On-center ganglia have a higher rate of action when light is confined to their center field rather than a uniform distribution of light across the visual field
What is the importance of the fact that there is increased activity from the light-dark edge?
the retina gives special importance ( by sheer volume of activity) to better distinguish differences in luminance
Bipolar cells have graded potentials or action potentials?
graded
Graded depolarization of bipolar cells releases (more/less) (blank) neurotransmitter
more glutamate!
on-center ganglia have what types of neurotransmitter receptors?
AMPA
kainate
NMDA
Off-center ganglia have (blank) class of receptors, and specifically which two?
ionotropic
AMPA
kainate
On-center ganglia have a (blank) class glutamate receptor called?
metabotropic
mGluR6
Glutamate does what to the potential of on-center ganglia?
depolarize
Glutamate does what to the potential of the off-center ganglia?
hyperpolarize
Light stimulation of the surrounding field alters horizontal cell potential how?
it hyperpolarizes
Light stimulation of surround field leads to what change in horizontal cell neurotransmitter release?
they release LESS GABA onto the photoreceptor terminals
What is the effect of decreased GABA on photoreceptor terminals?
it depolarizes the center cone terminal, offsetting the hyperpolarization from the center cone
What layer of the retina are the cell bodies of the photoreceptors in ?
Outer nuclear layer
In what layer are the connections between the horizontal cells and the photoreceptors and bipolar cells?
Outer plexiform layer
What cell bodies are in the inner nuclear layer?
Horizontal cells
Amacrine cells
Bipolar cells
the inner plexiform layer contains synapses between which cells?
Amacrine cells, bipolar cells, and ganglion cells
Gaglion cells are in which retinal layer?
Ganglion cell layer, derp
