Physiology Of Vision

Front 1

wavelength and colors of visible radiation

visible light

Back 1

visible light: 380-750 nm

gamma rays
x-rays
UV light
VISIBLE LIGHT
infared
radio wave

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Wave photon duality

Back 2

light travel in wave-like fashion with single packets of energy called photons

Front 3

visible spectrum

Back 3

ROY G BV
r: 730nm
o: 680nm
y: 630nm
g: 550nm
B: 480nm
v: 380nm

Front 4

color of an object

Back 4

depends on which wavelength is reflected back to the retina (not absorbed by the object)

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white and black

Back 5

white: all wavelengths reflected by object

black: all wavelengths absorbed by object

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Light Refraction

Back 6

light will bend when it passes from one medium to another

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Convex Lens

Back 7

thicker at center, tapered at edge

causes light to bend so that ir comes together at a focal point

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Real image

Back 8

image of a focal point of convex lens

inverted and reversed

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Cornea

Back 9

constant (unchanging) refraction

Front 10

Lens

Back 10

can change refraction and focal length
ciliary muscles change convexity of the lens

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far point of vision

Back 11

distance beyond which lens will not change its shape (20 feet)

Front 12

emmetropic eye

Back 12

normal healthy eye

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acccomodation of lens

Back 13

lens shape becomes more convex

light rays bend more sharply

shorter focal length for the closer object (ciliary muscles for lens)

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near point of vision

Back 14

shortest distance for focusing (maximum convexity of lens) about 8-10 inches, gets worse with age

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presbyopia

Back 15

poor close vision in elderly

inelasticity of lens

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accomodation of pupils

Back 16

constriction of pupils
better focus
less divergent rays
(constrictor muscle of iris)

Front 17

convergence of the eyes

Back 17

eyes rotate medially to keep image on center of the retina
(medial rectus muscles of the eyeballs)

Front 18

myopia

Back 18

nearsighted

distant objects are blurred, close objects are focused in from of the retina
(rather than directly on it)
eyeball too long, lens too strong
concave lens can correct light before eye

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hyperopia

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"farsightedness"
close objects are blurred
close objects are focused beyond the retina (rather than directly on it)

eyeball too short, poor refraction of lens
convex lens can correct light before eye

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astigmatism

Back 20

blurry images at all distances
unequal curves on lens and or cornea
creating discontinuous image on the retina

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pigmented base of retina

Back 21

outer segment (pigmented disc)
connecting stalk
inner segment (mitochondria)
outer fiber
cell body (nucleus)
inner fiber
synaptic ending

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"neural layer"

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bipolar cell
ganglion cell (axons carried to brain by optic nerve)

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outer segment

Back 23

contain membrane bound discs with pigments that absord and react to light

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rods

Back 24

pigment discs stacked like pennies all the way to the base, membranes are distint crom the plasma membrane

sensitive to dim light
respond to all wavelengths of color
only grey information to the brain
100 rods per ganglion cell to brain
widely spread throughout retina
not good for visual acuity

Front 25

cones

Back 25

pigment discs taper off toward the base, membranes are continuous with the plasma membrane
require bright light for stimulation
different cones have different pigments specific for certain wavelengths (colors)
can convey color information to brain
1-3 cones per ganglion cell to brain
primarily concentrated in fovea (center)
essential for visual acuity

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opsin

Back 26

transmembrane protein in the membrane of pigmented discs of rods and cones

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retinal

Back 27

light absorbing molecule that changes shape when struck by a photon of light

Front 28

vitamin A

Back 28

precursor of retinal

Front 29

11-cis isomer of retinal

Back 29

non-activated form of retinal, prior to absorption of photon energy, has a "kinked" double bond

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all trans isomer of retinal

Back 30

activated form of retinal, after struck by photon of light, double bond straightens out

Front 31

all trans isomer of retinal

Back 31

activated form of retinal, after struckt by photon of light, double bond straightens out

Front 32

rhodopsin

Back 32

visual pigment in rods
in membrance of pigmented discs of outer segments

Front 33

bleaching of pigment

Back 33

breakdown of rhodopsin after the absorption of light

11 cis retinals (+ scotopsin)-> rhodopsin -> all trans retinal (light + scotopsin)

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all trans retinal

Back 34

causes hyperpolarization of rod

Na+ channels open in dark are closed
rod is hyperpolarized (increase negativity)
Ca2+ channels in synapse close
less neurotransmitter released by the rod

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photopsins

Back 35

3 distint pigment in cones are sensitive to 3 different parts of the visible spectrum

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blue cones

Back 36

maximum sensitivity at 455 nm

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green cones

Back 37

maximus sensititvity at 530nm

Front 38

red cones

Back 38

maximum sensitivity at 625 fm

Front 39

different colors

Back 39

differential activation of each of the three different cones

Front 40

color blindness

Back 40

inherit gene for one of the photopsin proteins that is deficient (mainly male), most common are red and green mutations

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Light Adaptation

Back 41

very dark -> very light
rhodopsin in rods is quickly bleached out
sensitivity to shallow light disappears
rods inhibited by other retinal cells
cones are activated to take over (5 mins)
consensual pupil reflex - constriction

Front 42

Dark Adaptation

Back 42

very bright -> very dark
cones are gradually cease to be stimulated
bleached out rods can produce rhodopsin
rods eventually take over in the dim light
pupillary dilation pupils increase size

Front 43

nyctalopia

Back 43

defiency in function of rods during dim-light situations

vitamin A deficiency

Front 44

visual pathway - photoreceptor to occipital cortex

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retina - photoreceptors (rods and cones), bipolar cells, ganglion cells (axon = optic nerve)
axon path - optic nerve (from each eye retina), optic chiasma (medical fibers cross over), optic tracts (opposite visual fields)
thalamus - lateral geniculate body of thalamus
axon path - optic radiation (fibers to cortex)
cerebral cortex - occipital lobe, primary visual cortex
Most IMPORTANT
THALAMUS-LATERAL GENICULATE BODY OF THALAMUS

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superior colliculi

Back 45

control of extrinsic eye muscles

Front 46

pretectal nucleus

Back 46

mediate pupillary light reflexes

Front 47

suprachiasmatic nucles of hypothalamus

Back 47

circadian rhythm

Front 48

binocular vision

Back 48

two eyes have overlapping regions of the visual field, so that the same point is from slightly different angles

Front 49

depth perception

Back 49

a result of binocular vision in which a person can perceive relative distances based on information gathered in both eyes