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53 Cards in this Set
- Front
- Back
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What are the sense-organ aspects of the eye?
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a. Rods and cones are the receptors
b. These synapse on bipolar cells c. Bipolar cells synapse on retinal ganglion cells d. Horizontal cells contact both receptors and bipolars e. Amacrine cells contact both bipolars and retinal ganglion cells f. Axons of the retinal ganglion cells are the optic nerve |
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Which cells of the eye create action potentials?
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amacrine and retinal ganglion cells
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How many rods in the eye?
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100M
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How many cones in the eye?
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4M
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How many ganglion cells in the eye?
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1M
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What system responds only to intensity, not wavelength?
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Scotopic
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What are the aspects of the Scotopic system?
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1. Involves the rods
2. Works in dim light |
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What system responds to wavelength?
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Photopic
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What are the aspects of the Photopic system?
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1. Cones and color vision
2. Requires more intense light (you don't see colors in the dark) |
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What chemical do all photoreceptors use? What are they attached to?
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Opsins.
RETINAL |
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What kind of opsins do rods use?
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rhodopsin
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How do the use of opsins work?
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Quanta of light dissociate the opsin from the RETINAL, which combines with a G protein (transducin; it most closely resemble the gustducins), which uses phosphodiesterase (PDE), a catalytic enzyme, to transform cyclic GMP to 5'-GMP.
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What does 5'-GMP do?
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5'-GMP causes Na+ gates that are normally open to close. This is a vast cascade: one photon can result in blocking 1 million Na+ ions from entering.
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How many midget bipolars do cones attach to?
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2
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How many diffuse bipolars do cones attach to?
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2
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How many cones per midget bipolar?
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1
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How many cones per diffuse bipolar?
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Many
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What neurotransmitter do all rods and cones release?
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glutamate
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What are the three ways the visual system copes with intensity differences?
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1. Pupil size
2. Range fractionation 3. Adaptation |
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What is range fractionation in reference to light intensity?
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Some receptors require many more photons than others to fire
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What is adaptation in reference to intensity?
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receptor adjusts to prevailing level of light (so things don't get "grainy"
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How does the eye adapt for intensity?
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Adjusting the amount of Ca+2 available
adaption is limited by the recombination of the opsins and RETINAL Availability of chemicals (PDE, GMP, etc.) for activation: abundant at low light levels, much rarer at higher intensities |
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What is the fovea?
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The center of the visual field
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Where is the concentration of rods the highest?
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a ring 20 degrees from fovea
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What are scotomas?
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Perceptual gaps
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What is the main pathway for visual information in the brain?
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optic nerve --> optic chiasm --> optic tract --> lateral geniculate nucleus (LGN) of thalamus --> optic radiations --> calcarine sulcus of the occipital cortex
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What is the secondary pathway for visual information in the brain?
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optic tract --> superior colliculi. These are polymodal.
Another set of axons goes to the hypothalamus. |
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What is V1?
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The primary visual cortex.
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Both bipolar and retinal ganglion cells have what kind of shape?
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center-surround
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How many layers does the LGN have?
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6
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The Four dorsal (outer) layers of the LGN are what kind of cells?
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parvocellular (small)
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The two ventral (inner) layers of the LGN are what kind of cells?
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magnocellular (large)
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What are the parvocellular cells of the LGN responsible for?
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detect color
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What are the parvocellular cells of the LGN derived from?
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midget bipolars
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What are the magnocellular cells of the LGN responsible for?
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detect motion but not usually color
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What are the magnocellular cells of the LGN derived from?
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diffuse bipolars
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What structure does the LGN reflect?
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retinal ganglion
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Describe P retinal ganglion cells
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small, need high contrast, respond to color, have tonic responses; do not respond to motion
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Describe M retinal ganglion cells
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large, have large receptive fields, respond to motion but not color, and are phasic responders
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What are the rough percentages of P and M retinal ganglion cells?
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P = 80%
M = 10% |
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What purpose do V2 cells serve?
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V2 cells are similar to V1, but also respond to illusory contours(i.e., are responding to relationships among parts of receptive field)
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What purpose do V4 cells serve?
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V4 responds to sinusoidal gratings (i.e., this is the Fourier analysis), but also to concentric and radial stimuli, and to wavelength
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What purpose do V5 cells serve?
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Motion Detection
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What purpose do inferior temporal region cells serve?
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complex shapes that have been previously learned. This is where the "face" and "hand" cells are.
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What four dimensions are represented in the primary visual cortex?
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Location in space; orientation; color; ocular dominance
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What are ocular dominance columns?
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Alternating stripes representing the two eyes separately.
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What are the two major color theories?
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Trichromatic hypothesis and the Opponent-process hypothesis
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Explain the tri-chromatic theory as originally proposed.
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Three types of cones with three preferred wavelengths
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Explain the current trichromatic theory
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Rather than different "color detectors" three different cones have short (S), medium (M), and long (L) peak responses
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What cells show opponent-process behavior?
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Some retinal ganglion cells and all Parvocellular LGN cells
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What area of the visual cortex is used to interpret opponent-process information?
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V4
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What part of the visual cortex is involved in the "what" aspect of visual processing?
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Involves more of parvo pathway, and is more ventral
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What part of the visual cortex is involved in the "where" aspect of visual processing?
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Involves more of magno fields, and is dorsal, i.e. endpoint is V4 and V5
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