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110 Cards in this Set

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  • Back
What modality makes up the majority if our cortex
vision
How many layers does the eye have
3
What is the outermost layer of the eye and what is it made up off
The outer most layer is made up of sclera (white of the eye) and the anterior 1/6th of this layer is made up of cornea (clear part of the eye)
What is the function of the cornea and where is it located
Cornea is the first place where the light hits the eye, it focuses light and has refractory power, it located in the outermost layer, it makes up the anterior 1/6th of the sclera
What is middle layer of the eye
All the structure located here are called uveal tract and the choroid(deeply pigmented) makes up the biggest portion, anteriorily it makes up the ciliary body that has the ciliary muscles located in it and stroma of the iris
what is inner most layer of eye
Retina
What is the most vascualr layer of the eye
Uvea or middle layer, this is located b/t sclera and retina
Where does the neural processing take place in the eye
At the inner most layer or retina
Where is choroid located
In the middle eye
How is shape of the eye maintained
It is maintained by the intraocular pressure by the fluid located inside the eye
What is the colored portion of the eye called
Iris
What is the white portion of the eye called
sclera
What is the fluid that exerts intraocular pressure called
Aqueous humor
How is aqueous humor secreted
It is secreted by the ciliary body, which makes it and secretes it into the posterior chamber
How is aqueous humor drained
It is drained by canals of schlemm
What happens if there is too much intraocular pressure
Glaucoma
What is papilledema
When the intracranial pressures ↑, it pushes up on the meninges, this pushes up on the subarachnoid space and interferes with the axonal transport to the optic nerve. If this pressure ↑ continuously, it will lead to engorgement and elevation of the optic disk and will cause hemorrhage
What is vitreous humor
It is behind the lens, makes up 80% volume of the eye and has phagocytic function and clears up the debris
What is output
It is layer of neuronal cells called retinal ganglion cells, the axons of these cells comprise optic nerve
Light hits what part of the eye first
Cornea
What is the most powerful focusing element of the eye
Cornea, it is 2x more powerful than lens,
What is a diopter
It is inverse of focal length and is used to describe the power of the lens, D=1/fl
What is the diopter of cornea vs. lens
Cornea = 40, lens=20
What is a convex lens
It is like a prism and bends the light in a way that it focuses on a common point,
What is a focal point
Point when light passed through the prism comes to a common point
What is the focal length
Distance between the focal pt. and the lens
What does a convex lens with thin or less curvature signify
Long focal length
What does a convex lens with thick or more curvature sig
Short focal length
How is focal length determined
It is determined by the shape and size of the lens
What does a concave lens do to the focal length
It lengthens the focal length
What is cataracts and what is the common cause
It is opacities of the lens or loss of clarity of the lens and mainly caused by excessive UV damage
What is the image that is formed
As light passes through the lens the image that is formed is inverted and reversed
Where does the image from lens form
It forms on the retina
What is myopia and what causes myopia
Near sightedness, caused by too thick cornea or eye ball too long
What is hyperopia
It is far sightedness, caused by low refractive index and eye ball being too short or cornea too thin
How is myopia or hyperopia corrected
They are corrected by contacts or glasses that are + for hyperopia and – for myopia
What is the job of the cornea and lens
Bend the light in a way so that our photoreceptors can see a focused image
Accommodation
Is the process by which we can change the length of our lens to ↑ our refractive period
What does accommodation depend on
2 things the internal recoil force of the lens and exterior force generated by ciliary muscles attached to zonule fibers
Distant object what happens
Zonule force dominates the lens internal elasticity, the lens flattens
What happens if a product is brought close to us
The lens internal elasticity wins and the lens rounds up
What happens to zonule fibers when the ciliary muscles contract
The lens tension is exerted on the zonule fibers and they relax and the lens rounds up
What diopter can we achieve with accommodation
We can go from 20D to 34D
What happens to accommodation with age
It is reduced and we only go up to 21D
What is a another way to ↑refractive power
We can do so by decreasing the size of our pupil
What is the pupil
It is the aperture of our lens, increases the depth of the field
How is changing the pupil possible
Pupil is the aperture of the iris and iris is innervated by the PS and Sym. S
What does PNS innervate
It innervates the sphincter muscles of the iris
What innervates the dilator muscles
Sympathetic muscles
What are the 3 physiological events involved with accommodation
Pupil shortens, eyes converge, and eyes accommodate
Where is light energy converted to the electrical energy? what does that organ do
Retina, it send this info to the brain and brain constructs an image that can be recognized by our eyes
What is + in the presence of a lot of light
Cones
What kind of vision are the cones responsible for
Color vision
What kind of cells are + in low light
Rods, they can detect even a single photon of light
What are the out put cells from the retina
Ganglion cells
What do ganglion cells do
They send their axons to the brain via (optic nerve) and this tell the brain about the signals detected in the retina
These cells relay information from the photo receptors to the brain
Bipolar cells
What are the bipolar cells
They are rod bipolar and cone bipolar
What are the interneuron that mediate lateral interactions between layers of the retina like inner and outer plexiform layers
Horizontal and amacrine cells
What does pigment epithelia do
It releases growth factor and phagocyses outer segment
What is the mechanical connection between retina and the pigment epithelia? Weak or strong? And what does it cause?
It very weak and leads to retinal detachment
What happens with retinal detachment
Retina depends on the pigment epithelia for nourishment like GF and if that’s gone, it leads to photoreceptors stop working because they are isolated from the choroid vasculature
What do bipolar cells do
They are direct conduits from photoreceptors and synapse directly onto the ganglion cells
What is the pathway when the light enters the eye
Light hits the rods and cones and they release NT on Bipolar cells, w/c then release NT on to ganglion cells
What type of cells are responsible for lateral integration
Horizontal and amacrine cells
Where does the light hit on Rods and Cones
On the outer segment
What type of protein is found in the outer segment of Rods and cones
Opsin
What is opsin and what is it called in rods
In rods it is called rhodopsin and it is small light absorbing G-protein
What is the process of phototransduction
The light enters and hits the outer segment of the rods, this causes a conformational change in a small light absorbing G-protein receptor called opsin. Opsin depends on a small molecule called retinal. When the light hits rhodopsin retinal undergoes a conformational change and alters rhodopsin conformation. This allows the + of heterotrimeric G-protein, called transducin, the a-subunit of transducin exchanges a GDP for GTP, and dissociates form the beat and gamma subunits and gets +, this then + a phophodiesterase which lowers the amount of cGMP . Since the cell has many cGMP gated voltage channels, and now less cGMP comes in, and less current comes in and the cell hyperpolarizes and releases less NT
What is rhopdopsin and what does it depend on
It is opsin inside the rods and it depends on retinal
What is transducin
heterotrimeric G-protein, w/c when + can cause + of a phosphodiestrase and that leads to low cGMP levels and therefore hyperpolariztion of cell and less release of NT
What kind of potential do photoreceptors launch
They launch local potentials, they cannot launch action potentials
What type of cells in the aye are capable of launching an AP
Only ganglion cells
The release of NT released by photoreceptors depends on
The stimulus, in this case it is the amount of light
How is photo transduction signal terminated
Arrestin is + it prevents the rhodopsin from activating transducin and that way the retinal dissociates fro rhodopsin
Why should the photoreceptors be located at the back of the eye
Because rods and cones both have to be next to the pigment epithelium and the choroid
What kind of purpose do rods and cones serve
They recycle the shed disks of the outer segments
What kind of visions is mediated by the rods
Scotopic
When are rods used the most
During the conditions of low light
If you are looking at the stars, what kind of vision are u using, and what cell mediates it
You are using scotopic vision and the rods are mediating it
What happens if the rods are not working
Night blindness, you have trouble seeing in low light
What is rods sensitivity to light
It is very high, they can detect even a single photon
What kind of vision is mediated by the cones
photopic
When are cones used the most
During high light conditions
What happens if you lose the cones
Legally blindness
What is the cone sensitivity to light
Not as high as rods, require about 100 photons
What cells mediate our everyday vision
Cones
What molecule is important for cones to work properly
11 cis-retinal
What cells do our color visions
Cones
How many classes of cones are there
Three, long, medium and short
What are the classes of cones depnd on
Their ability to absorb photons
What color is absorbed via long spectra cones
Red
What color is absorbed via short spectra cones
blue
What color is absorbed via medium spectra cones
Yellow green
2 things, 1 is same in all cones and 1 is different based on their spectra
11 cis retinal is same and they all use different opsin
What does opsin determine
It determines the cones ability to absorb a certain intensity of the light
Does our vision depend more on one type of cone as opposed to the other
No, we equally depend on all three cones
When we come with a color of light, like red, and it is absorbed by the cell, what is cells response
It hyperpolarizes
Which sex has higher incidence of color blindness and why
Males, because the genes are located in the x-chromosome
What is fovea and where does it lie
Fovea lies in a depression the macula lutea and it has the highest visual acuity
Where does the macula lutea lie
It lies near the optic disk
What is significant about the optic disk
Optic disk has no neurons and it makes our blind spot, and it is in here that all the axons of the ganglion cells leave and make up the optic nerve
What cells are found in higher density
Cones are higher than rods
What is the central part of fovea called and what is absent from it and what is in high abundance
Foveola, no rods, and cones are in high number
Is foveola a vascular or avascular structure and what is the significance
It is avascular, it renders cones highly dependent on the PE and choroid
What is the main reason for such a high visual acuity in fovea
Increased connectivity of the cones
What is the difference between the circuitry in the fovea as opposed to rest of the retina
In the fovea the connection is 1-1, i.e. one cone will synapse on one bipolar cell and that one bipolar cell will synapse on one ganglion cells and that way the acuity is heightened
What is the ganglion cell in the fovea called
It is called midget cell ganglion and it has a very small receptive field
Why is the visual field less in rest of the retina
Because of convergence, in parts of retina other than fovea, the rods and cones can converge. For example, the rods in other part of retina, the rods to bipolar ratio is 15-1
Does convergence result in fine resolution
No, since things are converging, all it means is that there are too many impulses, so no fine resolution but instead these are fast conducting cells and all they transmit is that there is an impulse i.e. fast and sensitive