retinal phototransduction and signal processing Flashcards
what structure of the eye focuses far objects?
the cornea
what structure of the eye focuses near objects?
the lens
What structure of the eye converts light energy into electrical signal?
the retina
what structure of the eye provides nourishes the cones and rods?
the choroid
through what structure of the eye does light enter?
the cornea
what structure of the eye is the site of the highest spatial acuity?
the fovea
where do the axons converge to exit the eye?
the optic disk
what causes cataracts?
aggregates of protein that form in the lens
what do cataracts do to your vision?
cause clouding of the lens ( cloudy vision) and results in a glare especially at night
faded colors
what are risk factors for cataracts?
aging, diabetes, sunlight, smoking
what is presbyopia?
inability to focus on near objects
what is hyperopia?
farsightedness
glaucoma causes?
optic nerve damage and irreversible loss of peripheral visual fields and ultimately vision loss
what are the types of glaucoma?
normal tension
open angle
closed angle
what is open angle glaucoma?
progressive ( occurring over time) caused by obstruction of drainage of the aqueous humor which puts stress on the retina
what is closed angle glaucoma?
caused by a collapsed wall leading to a closed or narrow angle between the iris and cornea. this results in an acute increase in intraocular pressure and requires immediate care/surgery
where does intracular pressure increase?
in the front of the eye
what are the risk factors for glaucoma?
elevated eye pressure, thin cornea, abnormal optic anatomy, high blood pressure
what is the treatment for glaucoma?
eye drops to decrease the aqueous drainage production or keep it from increasing, or surgery
what does the retina do?
contains neurons that absorb light and process visual information in the images and send that information to the brain.
where do photoreceptors point?
toward the back of the eye
What are the 5 types of neurons found in the retina?
photoreceptors horizontal cells bipolar cells amacrine cells ganglionic cells
describe the flow of vertical information in the retina
info flows from photoreceptors to the bipolar cells to the ganglion cells and the cells release glutamate
describe the lateral flow of information in the retina
it is mediated by horizontal cells and amacrine cells and these cells release glycine or GABA
does a rod bipolar cell or a cone bipolar cell make 1 to 1 connections with cones?
rod bipolar cells contact cones 1 to 1
does a cone bipolar cell or a rod bipolar cell make several contacts with cones?
a cone bipolar cell makes several contacts with cones
where in the retina does phototransduction occur?
in the cilium aka the outer segment
what is in the inner segment of the retina?
nucleus, mitochondria, golgi, ER etc
what are the two types of photoreceptors?
rods and cones
how does the membrane potential of photoreceptors compare to that of most other neuron membrane potentials?
it is relatively depolarized rather than hyperpolarized at the resting potential ( near -40 mv)
what is graded hyperpolarization?
the way in which photoreceptors respond to light i.e. the more they are exposed intense light the more they HYPERPOLARIZE ( thus they DON”T form action potentials
IN dark light what is the [ cGMP] and how does that effect ionic influx/efflux and membrane potential?
in the dark there is an increase in [cGMP] which leads to an influx of Ca2+ and Na+ and an efflux of K+ leading to depolarization
IN dark light what is the [ cGMP] and how does that effect ionic influx/efflux and membrane potential?
in the light there is an decrease in [cGMP] which leads to an efflux of Ca2+ and Na+ and an influx of K+ leading to hyperpolarization
Why is it that the phototransduction cascade provides high amplification of a single photon?
because 1 rhodopsin closes 200 cGMP channels which leads to a significant glutamate and a hyperpolarization
what is rhodopsin?
g coupled receptor that is the primary light detector . it is a visual pigment protein that contains light absorbing chromophore 1-cis retinal ( an aldehyde of vitamin A)
how does light absorption change the retinal?
it changes the conformation from 11-cis to all-trans
what is dark adaptation?
when your eyes adapt to see in the dim light ( like in the movies)
what happens to retinal during dark adaptation?
the retinal is restored from a all-trans conformation to an 11-cis conformation ( this is called the visual or retinoid cycle.) and it is transported back out to the outer segment of the retina to recombine with opsin and form pigment.
what type of photoreceptor is found in great density in the periphery?
rods
what type of photo receptor is found in great density in the center of the eye ( the fovea) ?
cones ( lots of Cones in the Center)
where is there high spatial acuity in the eye and why?
in the fovea there is high spatial acuity and ( high resolution and low sensitivity) because there are lots of cones
where in the eye is there low resolution and high sensitivity?
in the periphery because there are more rods than cones
what is pushed aside in the fovea ganglion cells to allow for higher acuity?
the inner plexiform layer and the inner nuclear layer ( see pg 372 top left)
1 cone —> 1 cone bipolar cell ( _________ bipolar cell)
midget
what is scotopic vision?
rod- only vision: high sensitivity, low acuity, no color
what is photopic vision?
(cone only vision) low sensitivity, high acuity, color
what is mesopic vision?
cone and rod vision are active together
What is retinitis pigments?
a genetic eye disease that leads to night blindness. tunnel vision and legal blindness usu by age 40.
no treatment is available.
what is the cause for retinas pigments?
a mutation of genes for rhodopsin and other rod proteins lead to the degeneration of rods and eventually cones.
what is an electrortinogram?
it is a brief change in potential evoked by a large field flaw of light to the eye recorded with a contact lenses electrode
it provides a measure of retinal function
what is the leading cause of vision loss?
age-related macular degeneration
what disease is caused by abnormal blood vessels behind the retina growing under the macula, leaking and rapidly damaging the retina?
wet age related macular degeneration
what is the more common form of age related macular degeneration?
dry age related macular degeneration
what symptoms are associated w/ in macular degeneration?
loss of central vision
which photoreceptors are affect din macular degeneration?
there is a loss of cones
what disease is caused when yellow deposits accumulate ( drunsen)
dry age related macular degeneration
the RPE and photoreceptors of the macula degenerate
what are the symptoms of diabetic retinopathy?
blocked vision,: blurry vision with macular edema
what are the two ties of diabetic retinopathy?
NON-PROLIFERATIVE (hyperglycemia- induced pericyte death–> incompetence of vascular walls–> microaneursyms and dot and blot hemorrhages and PROLIFERATIVE ( new vessels grow whig leak blood)
which photoreceptors are affected in diabetic retinopathy?
none
what is the area of the retina that when stimulated elicits a change in the response in a neuron?
the receptive field
what is excitatory in the center and inhibitory in the surroundings?
the on center of the retina receptive field ( see pg 380)
what is inhibitory in the center and excitatory in the surroundings?
the off center of the retina receptive field ( see pg 380)
on center cells increase their dischargee rate to luminance __________ in the receptive field center
increments
off center cells increase their dischargee rate to luminance __________ in the receptive field center
decrements
why is it that when two different shades a darker and lighter are lined up next to each other there are differences in illumination ) edges)? ***
see page 381
where is the contrast between light and dark “first decided”?
the first synapse i.e. the synapse between the photoreceptor and the bipolar cell .
therefore the cones and rods don’t know what light is on or off because it is the first synapse that determines this
do on center bipolar cells depolarize or hyperpolarize in response to light?
they depolarize in response to light and hyper polarize in response to dark.
the off center bipolar cells do the opposite.
how many bipolars cells does each cone connect to?
two an on and an off bipolar cell
how many cones does each bipolar cell connect to?
one
which synapse is inverting?
the synapse between the on center bipolar cell and the photoreceptor
( closes the channel)
which synapses are non- inverting?
- btw the off center bipolar cell and the photoreceptor ( opens the channel )
- btw the off center bipolar cell and the off center ganglion cell
- btw the on center bipolar cell and the on center ganglion
these all use AMPA or NMDA
trichromatic facilitates distinguishing btw ?
red and green
color facilitates detecting?
borders btw objects
which cells antagonize bipolar cell response to light?
horizontal cells and amacrine cells
what is lateral inhibition?
inhibition that spreads from surround to center
dichromatic means you can differentiate between?
btw blue and green
what are the 3 cone types?
short (blue wavelength), medium (green wavelength), long ( red wavelength)
what causes colorblindness?
changes in the number of red and green cone opsins.
does each person have the same distribution of cones?
no but we have ability to detect differences in red and green
which ganglion cells tell the difference between blue and yellow?
koniocellular cells
which ganglion cells tell the difference between red and green?
parvocellular cells ( midget cells)
what do intrinsic photosensitive retinal ganglion cells do?
they exhibit pupillary control and they are involved in synchronization of circadian rhythms
