Ch 10
ch 10 vision
Terms
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- why do receptors have a great range of adaption?
- it adjusts its sensitivity to match the average level of ambient illumination (concered with change) to provide clear image (not grainy)
- off-center bipolar cell
- is inhibited by light in ceneter of its receptive field; turning off light excites cell because it recieves more glutamate depolarizing it
- when light stimlulates a photoreceptor what happens chemically?
- cell hyperpolarizes causing them to release LESS glutamate
- how many layers does the LGN have? what are they?
- 6 layers; four outer layers are called parvocellular (small cells), two inner layers call magnocellular (large cells)
- what are the two different functonal systems corresponding to the 2 receptor systems?
- scotopic system and photopic system
- off center ganglion cell
- activated when light is present to the periphery rather than centre; when light is turned off, off center bipolar cells depolarize (Excite) off center gang. cells
- fovea
- central portion of retina with dense concentration of cones (high acuity); rods located in periphery of retina
- photoreceptors
- cells in retina that response to light (100million)
- orientation column
- column of visual cortext hat tresponds to rod-shaped stimuli of particular orientation
- extraocular muscles
- 3 pairs of muscles that control the movement of the eyes
- optic disc
- where blood vessels enter and leave the eye where no photoreceptors are located therefore creating blind spot
- photopic system
- enables colour vivison so involves cones and diff. wavelengths
- cornea
- outer layer of eye that bends light rays and forms image on retina
- horizontal cells
- specialized retinal cells that contact both recepot cells and bipolar cells
- what are the 3 dimensions of colour?
- brightness (dark/light;intensity), hue (colour;wavelength), saturation (rich/faded; purity)
- rhodopsin
- photopigment in rods
- amacrine cells
- contact both bipolar cells and ganglion cells
- what are the three major characteristics of the visual system?
- sensitivity (weak stimuli amplified), integration (vision relatively slow), adaptation (wide range of light intensities)
- what three main factors help account for receptor adaptation in the visual system?
- role of calcium, level of photopigment, availability of retinal chemicals for transduction
- myopia
- nearsightedness develops when eyeball is too long forcing eye to focus on objects in front of retina rather than on the retina
- Tritanopia
- confuse yellow and blue rarer then confusion of green/red
- accommodation
- process of focusing
- lateral inhibition
- phenomenon by which interconnected nuerons inhibit their neighbors producing contrast at edges of regions
- explain the optic nerve cross over process at optic chiasm?
- axons from half of retina toward cheek (temporal retina) projects on same side of head, axons from half of retina near nose (nasal retina) cross over to opposite side of brain)
- ciliary muscles
- controls the shape of the lens which in turn focuses the image
- complex cortical cell
- cell in visual cortex that responds best to a bar of a particular size and orientation anywhere within area of visual field; some are binocular
- what kind of potentials do rods/cones/bipolar cells/horizontal cells generate? what does ganglion cells produce?
- graded local potentials, not action potentials; action potentials
- in the periphery of our visual system what do we detect best?
- motion within a range of speed most appropriate to movement of animals
- visual field
- whole are you can see without moving your head or your eyes
- what are the 4 dimensions of a visual stimulus that are represented in visual cortex?
- location in visual field, ocular dominance, orientation, colour
- visual acuity
- sharpness of vision (best at center of vision)
- trichromatic hypothesis
- hypoth. of color perception stating there are 3 diff. types of cones each excited by a region of the spectrum and have sperate pathways to brain
- what are the 2 types of photoreceptor cells?
- rods (long narrow; black/white)/cones (colour)
- spatial frequency filter model
- model of pattern analysis that emphasizes fourier analysis of visual stimuli (patterns of lines/edges at particular orientations)
- ocular dominance column
- region in coretx where one eye provides greater degree of input
- opponent process hypothesis
- theory that colour vision depends on systems that produce opposite responses to light of diff. wavelengths (compl. colours)
- scotoma
- perceptual gap in the visual field where nothing can be perceived
- what is the pathway for optic info?
- ganglion cells-->optic nerves-->cross midline at optic chiasm-->optic tract-->lateral geniculate nucleus (LGN) (visual part of thalamus)-->axons of LGN form optic radiations which go to occipital cortex-->primary visual cortex
- simple cortical cell
- in visual cortex that responds best to an edge or bar that has particular width as well as particular orientation and location in visual field; monocular
- what are the 5 steps to the evolution of the eye with lenses?
- concentrating light sensitive cells into groups that serve as photoreceptors, clustering light receptors at bottom of cuplike depressions (increased contrast of stimluli), closing the opening with transparent skin/substance (protection of receptors), forming a lens (improves focus)
- lens
- helps focus image on retina
- scotopic system
- works in dim light with rods therefore doesnt respond to wavelengths
- when the rods/cones release neurotransmitter molecules what is the path they take?
- bipolar cells-->ganglion cells --->optic nerve-->brain
- what are the two parts that make up rod/cone photopigments?
- retinal/opsin
- what are the two colour sensitive ganglion cells the retina contains?
- red-green, blue-yellow
- range fractionation
- different receptors with diff. thresholds handle different stimulus intensities
- on center ganglion cell
- activated when light is presented to centre rather tha periphery; if light turned on, oncenter bipolar cells depolarize (Excite) on centre ganglion cells
- on center bipolar cell
- excited by light in center of receptive field; turning light on excites because it recieves less glutmate
- Protanopia
- red cones fill with green cone opsin confusing the two colours
- Deuteranopia
- green cones fill with red opsin confusing two colours