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32 Cards in this Set
- Front
- Back
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Compound vs. refractive eyes |
Compound eye - great depth -> motion detection - detect wide variety of wavelengths - sensitivity to polarized light - covers larger angle/range Refractive eye - maximizes resolving power |
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Cornea |
- continuation of the sclera - major refractive element in the eye (air->liquid interface): 40/60 diopters of the eye |
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Glaucoma |
- flow in choroid blood vv. ↓ -> pressure buildup of aqueous humor (still produced) -> dmg of photoreceptors -> loss of peripheral vision |
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Accomodation |
- changing the refractive power of the lens by stretching/relaxing it -> focus - near vision: ciliary muscles contract -> lens relaxes/rounds -> highest refractive power |
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Presbyopia |
= Age-dependent loss in ability to focus on nearby objects (due to loss of elasticity of the lens) |
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Fovea |
Place of highest visual acuity (surrounded by macula): - cones w/ higher resolution predominate here - photoreceptors are closely packed here - other neuronal cells are pulled to the side -> less distortion |
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Macular degeneration |
- Wet - (pigmented epithelium & photoreceptors) tissue degeneration & abnormal vv. growth - Dry - deposition of yellowish protein & lipid aggregates = drusen |
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Neurons of the retina |
- photoreceptor cells (rods & cones) - bipolar cells - horizontal cells - amacrine cells - ganglion cells |
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Photoreceptor cell |
Outer segment - modified cilia; membranous disks (~1000) containing photopigments -> ↑A Inner segment - nucleus & synthetic machinery Synaptic terminal - NT vesicles - cells do not divide; disks renew -> phagocytosis |
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Rods vs. cones |
- Light detection: rods more sensitive => night (scattered light) vision - more photopigment, longer, better amplification, slower (graded integration), more convergence - Better daylight vision in cones - faster, better spatial resolution, sensitivity to direct axial rays, less convergence (almost 1:1 w/ bipolar cells), color vision (3 types of pigment/cells) |
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Phototransduction |
Light => rhodopsin (GPCR in discs): 11-cis-retinal -> trans-retinal -> transducin -> binds GTP -> PDE activation -> cGMP hydrolysis -> cGMP-gated Na/Ca channels close -> graded hyperpolarization --| dark current --| NT (glutamate) release [↓ inhibition] |
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Termination of response to light |
1) Ca-mediated feedback of cGMP metabolism - light -> Ca levels decrease -> ↓ inhibition of: -- rhodopsin kinase --| rhodopsin (binds arrestin) -- guanylate cyclase -> cGMP [ADAPTATION] 2) Recycling photobleached opsin (w/ disc) - RBP (retinal binding protein) delivers trans- retinol -> epithelial cells => retinol (VitA) =>11-cis retinal -> reused |
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Ganglion cells in the retina |
M-type (Magnocellular) - larger receptive field, motion detection P-type (Parvocellular) - smaller receptive field, color vision W-type - contain melanopsin -> photosensitive; importance for circadian rhythm (SCN, pretectum) & papillary reflex; homogeneous receptive field - otherwise: On-center; surround --| AP; Off-center; surround -> AP -- concentric organization due to horizontal cells --| photoreceptor -- On/Off due to Δ GluR's (excitatory [NMDA, AMPA] vs. inhibitory [Meta.]) => CONTRAST DETECTION |
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Treatment of vision loss |
- Stem cells/precursor therapy -> photoreceptor & lens cells - Development of photosensitive cells (using photoswitchable molecules) - Artificial lenses/retinas (retinitis pigmentosa, macular degeneration) |
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Projection of retinal ganglion cells -> brain |
Optic nerve -> optic chiasm (50% cross) -> optic tract -> - hypothalamus (SCN) - circadian rhythms - pretectum - reflex control (pupil & lens) - superior colliculus - head/eye orientation (aligned visual, auditory, somatic topography) - lateral geniculate nucleus (LGN) - point-to-point projection (topographic representation) |
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Pupillary reflex |
W ganglion cells -> pretectal area -> Edinger-Westphal nuclei (bilateral) -> CN III -> ciliary ganglion -> SM of pupillary sphincter (direct & consensual) |
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Retinal projections to LGN of thalamus |
P-type (Parvocellular) -> layers 3-6 -> color vision, fine shape discrimination M-type (Magnocellular) -> layers 1-2 -> movement, depth, contrast - also awake/asleep transition |
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Optic chiasm |
Decussation (50% = nasal ganglion axons cross) - temporal retina: Eph B1 - optic chiasm: Ephrin B2 ~ repulsive interaction in growth cone - nasal retina: do not express B1 -> decussate |
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LGN -> 1° Visual Cortex |
~ optic radiation - superior path -> above calcarine sulcus (upper retinal quadrants = lower visual field) - Meyer's loop (via temporal lobe) -> below ~ (inferior retinal quadrants = upper visual field) |
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1° Visual Cortex: information flow |
- vertical & horizontal info flow, 2 mm thick input: LGN -> layer 4 -> 2/3 -> 5/6 output: 2/3 -> other cortical regions (V2-5, A18, MT), 6 -> LGN - point-to-point projection: retina -> visual cortex => central symmetry image inversion |
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Visual deficits due to visual pathway lesions |
Monocular blindness - 1 eyeball dmg/CN II Anopsia - large visual field deficit - Bitemporal hemianopsia - optic chiasm compression -> nasal retinal bilateral information loss - Homonomous hemianopsia - any lesion more central than optic chiasm -> 1/2 visual field vision loss |
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Visual cortical cell classification |
Simple cell <- specifically orientated line Complex cell <- preferred orientation & length (receive input from multiple simple cells) Hypercomplex cell <- orientation, location, motion in a specific direction - consecutive convergence of visual information - vertical organization - stimulus specificity - horizontal organization - stimulus continuum |
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Ocular dominance columns |
- each column receives input from one eye, next to same visual field input from the other eye = hypercolumn (continual input transition) - blobs of cells ~ color, not orientation specificity |
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Transneuronal tracing |
- radiolabeled proline - used to trace projections from the visual system (inject retina -> see 1° VC) -> visualization of ocular dominance columns |
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Segregation of input from eyes |
~ Ephrin (8) & Eph (14) gradients: LGN -> 1° VC -> various combinations, attractive/repulsive - also coordinated electrical activity -> pruning (critical period): bilateral input necessary for development of ocular dominance columns - high level of plasticity (in impairment) |
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Eye synchronization impairments |
Strabismus - misalignment of the eyes due to lack of gaze coordination - esotropia = convergent - exotropia = divergent -> amblyopia (lazy eye) -> impaired vision from one eye (brain ignores input) |
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Visual processing |
V1 (A17) -> Motion detection (MT) - image/eye movement -> Depth perception (V2, V3) - binocular cells -> color vision (V4) - respective lesions of these areas result in - akinetopsia = motion blindness |
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Monocular cues for depth perception |
- previous familiarity - relative size - interposition - linear perspectiveness (line convergence, etc.) - shadows & illumination - motion parallax |
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Characteristics of color vision |
Constancy - based on wavelengths reflected & not absorbed (not based on illumination) Perception - hue (cone type stimulated), brightness (amount of stimulation), saturation (how much all cone systems simulated together) Gradation - 2M combinations of the above |
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Color opponent cells |
Single opponent cells Center surround organized ganglion cells -> color detection: Red/Green, Yellow/Blue, Blue/Red, etc. -> combine into double opponent cells (+/-) in the visual cortex |
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Binding problem |
- recombining the extracted information after parallel processing (feature maps): parietal cortex -> master map (cohesive perception) - selective attention inferior temporal lobe - complex visual ID (faces) |
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Higher order processing abnormalities |
Aperceptive agnosia = difficulty separating figures from background Prosopagnosia = inability to recognize faces Synesthesia = involuntary physical experience of cross-modal linkage |
