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Physio II: Exam 1 > L6: Vision I > Flashcards

L6: Vision I Flashcards

1
Q

define refraction

A

the bending of light waves at an angulated surface of a transparent material

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2
Q

light striking a perpendicular surface will ?

A

continue thru w/o bending

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3
Q

what does the degree of refraction depend on ?

A
  1. ratio of two refractive indices of the 2 medias

2. degree of angulation between the interface and entering waves

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4
Q

define refractive index

A

the ratio of the velocity of light in air to the velocity of light traveling in the substance

RI of air = 1.0

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5
Q

define refractive power

A

a measure of how much a lens bends light waves

measured in diopters

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6
Q

define diopter

A

1 diopter = 1 meter / focal length of lens

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7
Q

define focal point

A

the point thru which all parallel rays of light will pass

after passing thru the lens

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8
Q

define focal length

A

the distance from lens center to focal point

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9
Q

function of iris

A

controls the amount of light entering the eye

from darkness to light conditions

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10
Q

total refractive power of the eye

A

59 diopters

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11
Q

refractive indices of parts of the eye: cornea, aqueous humor, lens, vitreous humor

A 
cornea = 1.38
ah = 1.33
lens = 1.4
vh = 1.34
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12
Q

define emmetropia

A

a person with ideal/perfect vision

parallel light rays from distant objects come into sharp focus on the retina when ciliary muscles completely relax

all distant objects can be seen clearly

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13
Q

define hyperopia

A

farsightedness

being able to seen far objects clearly but closer objects are not clear

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14
Q

cause of hyperopia

A

usually due to an eyeball that is too short
or
occasionally a lens system that is too weak

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15
Q

define myopia

A

nearsightedness
cannot see distant objects but closer things are clear

when ciliary muscle is completely relaxed, light rays coming from distant objects are focused in from of the retina

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16
Q

cause of myopia

A

usually due to too long of an eyeball

compared to the focusing power of the eye

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17
Q

define visual acuity

A

a measure of the resolving power of the eye

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18
Q

average diameter of a cone
and
max visual acuity for 2-pt sources of light

A

average d for cone = 1.5 micrometer
thus
max va for 2-pt source is = 1.5 to 2 micrometers

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19
Q

depth of focus of the lens ______ as the pupillary diameter ______.

A

increases
decreases

negative relationship

20
Q

ions moved to create aqueous humor

A

ions drawn into space in ciliary apparatus created by 2 layers of epithelial cells

Na active trans in
Cl in
bicarbonate in

21
Q

how is aqueous humor

A

as the ions are drawn into the space
water follows via osmosis

thus creating an aqueous solution that is passed into the anterior chamber

22
Q

flow of fluid in the eye

A

fluid flows from:
ant. chamber
canal of schlemm
aqueous veins in sclera

23
Q

what is used to measure intraocular pressure?

A

tonometer

normal p = 15 mmHg

24
Q

how is a tonometer used?

A

eye is numbed and a stain applied

a tool is used to just touch the cornea and can measure the pressure w/in the eye

cheaper way but less accurate is the air pistol where they put a puff of air into the eye

25
Q

what is glaucoma?

why is it so dangerous?

A

increased fluid pressure in your eye

this increased p can damage the optic nerve and lead to blindness

the fluid drains too slow, so pressure slowly builds but it is painless so it can happen over years w/o notice

26
Q

photosensitive pigments in rods and cones

A

rods = rhodopsin

cones = 3 dif. color pigments

27
Q

list the functional parts of photoreceptors

A

outer segment
inner segment
nucleus
synaptic body

28
Q

outer segment

A

site of light sensitive photochemicals

29
Q

inner segment

A

contains organelles

especially mito

30
Q

synaptic body

A

connects w/ horizontal and bipolar cells

31
Q

how does light affect rhodopsin?

A

rhodopsin + light = converts 11cis-retinal to all trans-retinal

requires isomerase and metabolic nrg to return to normal

32
Q

metarhodopsin II

A

an intermediate between the transforming of retinal

it excites electrical changes in rods

33
Q

vitamin A is also called?

A

all-trans-retinol

an alternate pathway for all-trans-retinal to return to 11-cis-retinal

34
Q

results of an excited rod

A

–increased negativity of intrarod memb. potential (hyperpolarization)

35
Q

decomposition of rhodopsin ?

A

decreases rod memb. conductance for Na ions in the outer segment

resulting in hyperpolarization of entire rod memb.

36
Q

describe outer segment membrane of rods in dark

A

leaky to Na ions that flow thru cGMP-gated channels

this slow leak into cell neutralizes the negativity of the entire cell

thus reduced electronegativity in dark conditions
-40mV instead of normal -70 to -80 mV

37
Q

inner segment of rods

A

continuously pumps Na out and K in

K leaks out via non-gated channels

a negative potential is created inside cell

38
Q

when rhodopsin is exposed to light?

A

it begins to decompose

the retinal portion is activated and stims transducin (G-protein)

39
Q

active transducin

A

activates cGMP phosphodiesterase

which catalyzes cGMP to 5’GMP

40
Q

reduction in cGMP causes?

A

closure of Na channels

thus rod becomes hyperpolarized

41
Q

when rhodopsin is activated, __________ channels close for each ?

A

several hundred channels close

for each rhodopsin molecule activated

42
Q

cones are similar to rods except that the protein portions (_____) of the photochemicals are ?

A

opsins

are dif. from the scotopsin in the rod photochemicals

43
Q

colors cones are sensitive to?

A

blue
green
red

overlapping of light absorption spectrum results in humans ability to see wide number of colors

44
Q

wavelength of colors

A

blue = 390 - 530

green = 440 - 620

red = 480 - 690

45
Q

scotopsin + 11-cis-retinal = ?

A

rhodopsin

46
Q

rhodopsin + light = ?

A

scotopsin + all-trans-retinal

now that it is converted it will separate from scotopsin

47
Q

alternative pathway using Vit. A

A

all-trans retinal –> all-trans-retinol

all-trans-retinol –> 11-cis retinol —> 11-cis retinal

Physio II: Exam 1 (9 decks)

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