Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
41 Cards in this Set
- Front
- Back
|
Cornea |
refracts light to project image onto retina |
|
|
Lens |
helps refract light, focus image on retina |
|
|
Go over steps of visual processing |
use slides |
|
|
Two main portions of the retina |
nasal fields and temporal fields |
|
|
Nasal fields |
interior of the retina, closer to nose, projects contralterally |
|
|
Temporal fields |
outer portion of retina, close to ears, projects ipsilaterally |
|
|
Three layers of retina |
1) photoreceptors - rod and cones 2) intermediate neurons 3) optic nerve fibers |
|
|
Photoreceptors |
rods and cones |
|
|
Rod |
no color, dim light, outside fovea, low acuity Do not fire AP |
|
|
Cone |
color, bright light, inside fovea, high acuity
Do not fire AP Each cone has one of three classes of pigments, with each responding a a range of wavelengths |
|
|
Retina |
where visual processing begins, has three layers, contains ~100 million photoreceptors, visual system updates ~ 3 times/sec based on photorecptor activity |
|
|
Visual processing from the retina in terms of projections
|
Rod and cones project to bipolar cells which project to ganglion cells whose axons form the optic nerve. There are also intermediate neurons that provide more processing through lateral inhibition. Horizontal cells - by the photoreceptor/bipolar synapse Amacrine cells - by the ganglion synapse |
|
|
Bipolar cells |
Receive projections from the rod/cones. Do not fire AP |
|
|
Ganglion cells |
receive projections from the bipolar cells, and conduct AP, make up the optic nerve |
|
|
Acuity |
Sharpness of vision Highest in fovea |
|
|
Fovea |
central part of visual field; directly behind the pupil so there is less blood in front of it, therefore more light reaches it.
Contains the highest density of cones SO: this is area of highest acuity |
|
|
Rhodopsin |
a photopigment that captures photons, selectively, at different wavelengths.
Two parts: retinal and opsin Different cones captures different colors of light |
|
|
visible light of spectrum is between |
400 - 700 nm |
|
|
UV light spec |
less than 400 nm |
|
|
Infrared light spec |
greater than 700 nm |
|
|
Light spec order from shortest to longest wavelenth |
Gamma, Xray, UV, visible, infrared, radar, FM radio, TV, AM radio, AC circuits |
|
|
Range of wavelength peaks in retina |
420 nm for violet --> S cones 530 nm for green --> M cones 560 nm for yellow-green --> L cones 496 nm --> rods |
|
|
Light's effect on retina |
1) Under normal, no light condition, Na+ channels on photoreceptors are held open by cGMP. 2) Shine light, changing shape of retinal 3) rhodopsin dissociates into retinal and opsin - 4) opsin combines with and activates a g-protein called transducin (about 500 of these activated per rhodopsin) 4) Transducin activates phosphodiesterase 5) PDE converts cGMP to 5'-GMP (about 2000 cGMP per PDE 6) reduced cGMP causes Na+ channels to close 7) cell hyperpolarizes |
|
|
In photoreceptors the brighter the light, the _______ the hyperpolarization |
the greater |
|
|
Photoreceptor layout |
There is an inner segment and outer segment. Outer segment = contains many discs, each containing many rhodopsin proteins Inner segment = where hyperpolarity is measure, area where light passes first before reaching outer segement |
|
|
Hyperpolarizing photoreceptors decreases________ release |
glutamate. What effect this has depends on the bipolar cell/type of glutamate receptor maybe |
|
|
Bipolar will be inhibited by light if it is ________ |
off-center/on-surround, where light in the center of the field inhibits the cells |
|
|
Bipolar will be excited by light if it is ________ |
on-center/off-surround, where light in the center of the field excited the cells |
|
|
Which cells in retina have receptive fields? |
bipolar and ganglion
|
|
|
For on-center, If you illuminate the entire center... |
you see a large depolariation in the bipolar cell you see many AP in the ganglion cell |
|
|
For on-center, If you illuminate the entire surround... |
you see a large hyperpolarization in the bipolar cell you see a drop/few AP in the ganglion cell |
|
|
For on-center, If you illuminate the entire center and surround... |
you see a small depolarization in bipolar cell
you see sporadic/normal AP in the ganglion cell |
|
|
most axons from the optic nerve terminate on the.... |
lateral geniculate nucleus AKA visual thalamus |
|
|
Pathway of visual processing |
retina --> LGN --> Occipital cortex/visual cortex/prmary visual cortex/V1/striate cortex |
|
|
Optic radiation |
projections from the LGN to the PVC |
|
|
extrastriate cortex |
surrounding cortical regions are also critical for vision |
|
|
Lateral geniculate nucleus |
Cells here respond like retina, can also be activated by light 6 layers: Magnocellular - 2 inner layers that contain larger cells, not for color vision Parvocellular - 4 outer layers that contain smaller cells, for color vision LGN cells have concentric fields (like retina) |
|
|
Cells in the visual cortex respond to... |
more complicated stimuli, like things moving in a certain direction |
|
|
Magnocellular cells |
Have relatively large receptive fields, 2 inner most layers, larger cells, Input to here is from large ganglion M-cells Do not respond to color |
|
|
Parvocellular |
Have relatively large receptive fields, 4 outer most layers, smaller cells, Input to here is from small ganglion P-cells, that get input from cones Do respond to color |
|
|
Primary Visual cortex/visual cortex/occipital cortex/V1 |
Not very sensitive to light, need more specific stimuli About 50% of V1 is dedicated to the fovea |
