Exam2Lec4Vision:RetinalProcessing Flashcards
What is the region of high visual acuity in the eye?
macula/fovea
What is the blindspot of the eye?
optic disk
no receptors, this is where cells/axons leave retina to become part of the optic nerve
What is the vascular supply of the eye?
branch of opthalmic artery and branch of opthalmic vein
Most of our vision is ____
binocular
this is central vision (both eyes)
Most of our peripheral vision is____
monocular
one eye
Where is light absorbed?
retina
light perception begins at retina
How can the lens accomodate when light info enters?
It can change shape so that the light is refracted at the correct angle onto the retina
lens help focus light
To see far, what how does the eye accomodate?
- Ciliary muscle relaxes
- suspensory ligament taut
- lends flattens/thins
To see near, how does the eye accomodate?
- Ciliary muscle contracts
- Suspensory ligament lax
- lends becomes globular (thickens)
What is emmetropia?
Normal vision
What is myopia and where is the focal point?
near sightedness. focal point is in front of the eye
can see near, focus light in front of the retina,
What is hyperopia and where is the focal point?
far-sightedness and the focal pt is in back of the retina
can see far, light focuses behind the retina, cant see near
How do glassses/contacts help you see?
glasses/contacts changes the angle of light so it reaches the retina
Projections of the visual field/image onto the retina are ____
inverted (flipped upside down and backwards)
What you are looking at in space
Visual field
What’s projected onto the retina
retinal field
All information from the right visual field will end up on the ____ portion of the brain.
left
How does info from your right visal field end up on the left side of your brain?
- Info projects onto temporal regions of LEFT retina and nasal region of Right retina
- all info that projects to temporal stays ipsilateral. Info projected to nasal retina will cross to contralateral side
- So then its sents up left optic tract and left side of brain for processing
Given that each eye receives information from either visual field, fibers cross at the ____ to get information from the visual field to its respective cortical region.
optic chiasm
What are the two types of photoreceptors of the retina?
Rods and cones
What are the two types of photoreceptors of the retina?
Rods and cones
Where are rods located?
every where else in the retina (except optic disk)
Where are cones located?
Macula/Fovea
What are the 4 retinal neurons?
- Horizontal cells
- Bipolar cell
- Amacrine cell
- Ganglion cell
1 and 2 produce graded potentials and sends excitatroy signals to 3 and 4 which produce action potentials
Briefly explain how light reaches the retina?
- Light enters the superficial retina, passes through cell bodies, and travels towards the back in order to reach photosensitive cells (rods and cones).
- Action potential allows photoreceptor signaling to be sent back up towards the superficial retina where they can then be guided to the optic nerve and CNS.
What are rods highly sensitive to?
Low levels of light
not sensitive to color
What protein do rods have and do they have a large or small number of disks?
Opsin=rhodopsin
large number of disks
Rods have far larger areas of photoreceptor disks to make them highly sensitive to light.
What are cones sensitive to?
Cones are sensitive to colors
What protein do cones have and do they have a large or small number of disks?
Many (around 3) different opsins
smaller number of disks
diff opsons are responsible for detectong diff wavelenghts that gives us diff colors
What is the fxn of pigment epithelium?
It is a “backwards” organization of the retinal later due to the need for constant recycling of photoreceptor protiens (opsins) and disks
rods and cones photoreceptors are embedded here and recycles
Why do we need to recycle photoreceptor proteins and what is required?
on exam
Need to be constantly synthesizing new protiens so tha we stay sensitive to light especially rods (low light conditions). We need VITAMIN A retinol , this maintains rods and rhodopsin signaliong
50-85 of total body retinol is stored in liver
What is scotopic vision?
Only rods are being used
like an on/off switch, no wavelength to tell you color
What is mesopic vision?
Rods and cones are being used
you can see color
What is photopic vision?
only cones are being used (rodes are sat with light)
rods are sat with light so much that rods arent firing anymore, and we use cones
Which type of vision has the best acuity?
Photopic vision
bc cone and color info
Light sensitivity depend on ____ and ____.
receptive field size and intensity
Rods are usually activated at what wavelength of light?
400-600nm
What is trichromat?
This is normal vision; you contain all 3 cones subtype
have all 3 opsins
What is protanopia?
This is a type of colorblindness where you loose the cone subtype responsible for RED wavelengths
2/3 opsins, missing longest=red wl of light
pRo=Red
What is deuteranopia?
This is a type of colorblindness where you loose the cone subtype responsible for GREEN wavelengths
2/3 opsins, missing middle=green wl of light
Activation of this alters a membrane current that controls photoreceptor transmitter release
Rhodopsin
In the abscence of light, explain what happens to photoreceptor rhodopsin and its relation to glutamate
- Rhodopsin is INACTIVE
- Na+ channels opens and influx
- Cell is DEPOLARIZED
- HIGH rate of glutamate is released constantly
cones have the SAME signaling using different opsins.
With light, explain what happens to photoreceptor rhodopsin and its relation to glutamate
- Rhodopsin is ACTIVE
- Na+ channels CLOSED
- Cell is HYPERPOL
- Low rate of glutamate release
basically no glutamate released
cones have the SAME signaling using different opsins.
Explain briefly vertical info flow
- Rods and cones release glut
- This is inhibitors or excitatory depending in the glut receptors expresed on the bipolar cell
- Bipolar cells release glutamate which is excitatory for ganglion cells
ganglion cells=retinol ganglion cells (RGC)
Explain vertical info flow for ON center receptor field (light comes in)
Light stimulation causes
1.HYPERPOL of photoreceptor, and no glutamate is release
2. INCR DEPOL of ON center bipolar cell , so mGLU is activated
3. INCR glutamamte release from on bipolar cells
4. Incr gangliom cell firing rate
Explain vertical info flow for OFF center receptor field (light comes in)
Light stimulation causes
1. HYPERPOL of photoreceptor, and no glutamate is release
2. DECR dep of OFF center bipolar cell , so NMDA rec is INHIBITED (b/c hyperpol)
3. DECR glutamamte release from off bipolar cells
4. DECR ganglion cell firing rate
With light mention if the following are activated or inhibited?
A. On-center bipolar cell (mGlu)
B. Off-center bipolar cell (NMDA)
A. On-center bipolar cell (mGlu): ACTIVATED
B. Off-center bipolar cell (NMDA): INHIBITED
With NO light mention if the following are activated or inhibited.
A. On-center bipolar cell (mGlu)
B. Off-center bipolar cell (NMDA)
A. On-center bipolar cell (mGlu): INHIBITED
B. Off-center bipolar cell (NMDA): ACTIVATED
What variables contribute to mapping center-surrond receptive field of the retina?
- Duration of spot illumination
- Size of spot illumination
- Background light intensitiy of both center and surround area
center compated to peripheral environment
ex:a grey spot next to white looks much darker than the same grey spot next to black
What is 20/20 vision?
At 20 feet, a human with nominal eye performance is able to separate lines for image recognition
20/40 vision, at 20 feet a human is able to sep line for image recognition that a perosn with nominal performance can resole at 40 feet
What are the 2 types of synaptic transmission in the retina?
chemical and electrical
need electrical to identify things moving very quickly
What are the two cells involved in lateral information flow and explain their fxn
- Horizontal cells: release GABA (inhibitory) and form gap junctions.
- Amacrine cells: release GABA, glycine, dopamine (inhibitory) and form gap junctions
What is lateral inhibition essential for?
Essential for identifying shapes (edges) and detecting motion
Horizontal cells always have a ____ output via release of ____.
inhibitory, GABA
What are horizontal cells connected to?
Connected laterally to photoreceptor cells, and they suppress vertical information flow in adjacent pathways
Explain how horizontal cells play a role in lateral inhibition in this case, for an ON-center receptive field, with NO surround light stimulation
- There is a dark surround, this inhibits center cone via GABA
- Less glutamate release and stimulation of the one-center bipolar cells,
- Incr ganglion cell firing
Dark stimulated surround ____ on enter response
enhances/incr
Explain how horizontal cells play a role in lateral inhibition in this case, for an ON-center receptive field, WITH surround light stimulation
- Surround photoreceptor is activated and therefore hyperpol with decr release of glut
- Reduction of glut reduces release of GABA from horizontal cells
- Reduction of gaba inhibition causes dep of photoreceptors in the center and incr release of glut
- Incr release of Glu from photoreceptor causes a decr in ON center ganglion cells firing
Light stimulated surround ____ on center response
inhibits/decr
Lateral inhibition relies on what?
Gap jxns: provides cell-cell coupling
What does lateral inhibition promote and amplify?
Lateral inhibitions promotes contrast enhancement and amplifies edge detection of the retina
detect edges with shape
For information flow to the brain, the visual scene is encoded by the firing patterns of ____ ____ ____ , which is further processed in the ____ ____ by the way of the ____ ____.
retinal ganglion cells
visual cortex
optic nerve
What are the subtypes of retinal neurons?
- Photoreceptors
- Horizontal cells
- Bipolar cells
4.Amacrine cells
5.Ganglion cells
What is the lens retinal prosthesis?
A computer chip embedded in lens that mimic retina
