Introduction Flashcards
WIT: The study of monocular visual perception and its physiological basis and application to clinical practice
Psychophysics and Physiology & Monocular Vision (PPMV)
These cells have long axons that converge to the optic disc and form the 2nd cranial nerve
The ganglion cells
Where do the ganglion cells synapse?
The LGN
How does the striate cortex communicate between right and left visual cortex?
The corpus callosum
The central 10 degrees of the visual field occupies what percent of the striate cortex? It is overrepresented where?
50% of striate cortex
overrepresented in V1
Photopic conditions use what type of PR?
cones
Mesopic conditions use what type of PR?
Rod and Cone
Scotopic conditions use what type of PR?
Rods
Rods are essential for what type of vision?
Night vision
How many types of cones are there?
3 types
In scotopic conditions there is a loss of color vision and peripheral vision is used. What is the average luminosity threshold ?
507nm
In photopic conditions, central vision is used. What is the average luminosity threshold?
555nm
How many discs are in a rod? What are rods maintained by?
1000 discs
maintained by Vit. A and Opsin
What is the photopigment found in the discs? One disc contains how many molecules of this pigment?
Rhodopsin
10K molecules
How many photons are needed to elicit a visual response in a rod?
6-10 photons
How many photons are needed to activate a cone? How many cones are needed to elicit a visual response?
5 photons
2 cones
Cyanolabe cones are what color? What type of cone is it? What’s the wavelength?
blue
S cone (short)
426nm
Chorolabe cones are what color? What type of cone is it? What’s the wavelength?
Green
M cone (medium)
530nm
Erythrolabe cones are what color? What type of cone is it? What’s the wavelength?
Red
L cone (long)
557nm
WIT: The difference in sensitivity between scotopic and photopic systems for a given wavelength
Photochromatic Interval
The scotopic system is more sensitive to light than the photopic at all wavelengths except ?
in the long wavelength at 650 nm
At 650nm, the photocromatic interval is ___ because all rods and cones are equally sensitive.
0
WIT: The relative increase in the brightness of longer wavelngth stimuli as lighting conditions change from scotopic to photopic and back?
Purkinje Shift
The eye is most sensitive to what color during the day?
yellow-green
The eye is most sensitive to what color at dusk?
green-blue
When a rod or cone absorbs a photon it becomes ?
Hyperpolarized
50% of rhodopsin recovers in __ minutes, 50% of cone pigment recovers in __ minutes.
rod = 5 mins cone = 1.5 mins
PR are 1st order neurons considered to be _____ neurons
modified
In the dark, PR are _______. What inhibitory NT is released to block bipolar cells?
- PR are depolarized
- Glutamate is released
In the light, PR are _______. This allows vision to occur.
- PR are hyperpolarized
How many total PRs? How many rods? How many cones?
> 125 million PR
~ 120 million rods
~ 6 million cones
What % of vision depends on the cones?
99%
Where are there no PR in the retina?
- The ON
2. 15 degrees temporal to fovea
Where are rods packed most densely?
at 20 degrees from the fovea
Where are cones packed most densely?
at the fovea
90-95% of cone population are what types of cones?
L & M cones
S cones make up what % of cone population?
5-10%
In the fovea, inner retinal elements are pushed aside and light falls directly where?
on the cone outer segments
The foveola only contains what type of PRs?
cones
WIT: nonphotosensitive yellow pigment in the inner retina that absorbs blue light?
Macula Lutea
What are the 4 functions of the RPE?
- Provides metabolic support
- Provides structural support
- Storage of Vit.A
- Absorbs extra photons
The PRs synapse on what 2nd order neuron?
Retinal bipolar cells
A midget bipolar cell only contacts how many cones?
1 cone
A diffuse bipolar cell contacts how many cones?
5-10 cones
What cells are responsible for the horizontal transmission of retinal info? Are these cells excitatory or inhibitory?
Horizontal and amacrine cells
- both inhibitory
Horizontal cells receives in put from what?
PRs
Horizontal cells release what inhibitory neurotransmitter in response to a depolarized photoreceptor?
GABA
Amacrine cells receive input from what? What cell does it contact?
Bipolar cells
contacts ganglion cells
Amacrine releases what inhibitory NT to ganglion cells to stop them from firing?
GABA
Bipolar cells synapse on what 3rd order neuron?
Ganglion cells
approx how many ganglion cells do we have?
1 million
In the periphery, ganglion cells integrate information from how many degrees of the retina
3 degrees
For on-center ganglion cells, light causes what?
Light = excitation
For off-center ganglion cells, light causes what?
Light = inhibition
What are teh 3 types of ganglion cells?
- Parasol
- Midget
- Small bistratified
The ipsilateral eye projects to what layers of the LGN?
2,3,5
The contralateral eye projects to what layers of the LGN?
1,4,6
The 6 layers of the LGN have an upper and lower section. Upper contains what 3 things?
- Larger cell bodies
- Magnocellular Layer
- Parvocellular Layer
The lower layers of the LGN contain what 2 things?
- Smaller cell bodies
2. Koniocellular Layer
The magnocellular layer contains what 3 things?
- Larger Cells
- Magno (M-cells)
- Layers 1 &2 of LGN
The Parvocellular layer contains what 3 things?
- Smaller cells
- Parvo (P-cells)
- Layers 3 to 6 of LGN
The Koniocellular layer contains what 2 things?
- Small cells
2. Layers 1-6 of LGN
The magnocellular layer receives input from what ganglion cells?
Parasol ganglion cells
The parvocellular layer receives input from what ganglion cells?
Midget ganglion cells
The koniocellular layer receives input from what ganglion cells?
Small bistratified cells
The parvo retinogeniculate pathway does what?
details red and green color
The magno retinogeniculate pathway does what?
fast movement
The konio retinogeniculate pathway does what?
details blue and yellow color
What is the new photosensitive ganglion cell?
ipRGC (intrinsically photosensitive retinal ganglion cell)
What pigment does the ipRGC contain? What’s it’s wavelength
Melanopsin
- 480nm
What are the 3 functions of the ipRGC>
- maintain circadian rhythm
- Pupil control
- Release/suppression of melatonin in pineal gland
PRs send messages when they are ____.
hyperpolarized
Bipolar/Ganglion cells send messages when they are___?
Depolarized
What are the response, sensitivity and DA of rods?
- Large/slow response
- High sensitivity
- Slow dark adaptation
What are the response, sensitivity and DA of cones?
- Small/fast response
- Low sensitivity
- Fast dark adaptation