Physio II lecture 5 Flashcards Preview

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Flashcards in Physio II lecture 5 Deck (119):
1

What is refraction?

The bending of light waves at an angulated surface of transparent material-note that might striking a perpendicular surface continues on through without bending

2

What does the degree of every fraction, amount of bending, depend on?

The ratio of the two reflective indicates of the two transparent media and the degree of angulation between the interface in the entering wavefront of the light waves

3

What is the reflective index?

It is the ratio of the velocity of light and air to the velocity of light traveling in the substance ratio index of air equals 1.0

4

What is the refractive power

It is a measure of how much a lens bends light Waze. It measured in diopters

5

One diopter equals

1 m divided by the focal length of a lens

6

What is a focal point?

The point through which all parallel rays of light will pass after passing through each part of the lens

7

What is the focal length?

The distance from the center of the lens to the focal point

8

Compare the eye to a camera

...

9

How does the iris of the iPhone's and in a similar manner to the iris diaphragm of a camera?

It controls the amount of light entering the eye from darkness to light conditions

10

the depth of focus of the lens to increases

the pupillary diameter decreases

11

What is emmetropia?

A normal eye with regard to depth of focus, parallel light rays from distant objects are in sharp focus on the retina when the ciliary muscle is completely relaxed, all distant objects can be seen clearly

12

What is hyperopia?

farsightednessusually due to an eyeball that is too short or occasionally a lens system that is too weakall distant objects can be seen clearly

13

What is myopia?

nearsightednesswhen ciliary muscle is completely relaxed, light rays coming from distant objects are focused in front of the retinausually due to too long of an eyeball

14

What kinds of lenses would be used to correct hyperopia and myopia?

...

15

What is visual acuity?

A measure of the resolving power of the eye

16

What is the avg diameter of a cone in the retina?

1.5 um

17

What is teh maximum visual acuity for two point sources of light?

1.5 to 2 mm

18

What will light form a distant point source normally create?

a spot with a diameter of about 11 um and a center that is brighter than the periphery

19

Where is aqueous humor formed?

The ciliary processes

20

What does teh ciliary apparatus consists of?

two opposing layers of epithelial cells with a space btw them. Na ions are actively transported inot this space and are accompanied by Cl and bicarbonate ions

21

Where do Cl and bicarbonate ions draw water via osmosis into?

The space and the aqueous solution is then passes into the anterior chamber

22

How does the flow of fluid occur?

Fluid flows from the anterior chamber into the canal of Schlemm and from there into aqueous veins in the sclera

23

What is used to measure the intraocular pressure?

a tonometer-normal pressure is 15 mm Hg

24

glacoma

A group of eye conditions that leads to damage to the optic nerve

25

Photosensitive pegments in rods:

Rhodopsin

26

photosensitive pigments in cones:

three different color pigments

27

What are these photosensitive pigments?

transmembrane conjugated proteins

28

Outer segment

site of light sensitive photochemicals

29

inner segment

contains organelles esp mitochondria

30

synaptic body

connects with horizontal and bipolar cells

31

What are the major functional segments of the rod and the cone?

outer segmentinner segmentnucleus synaptic body

32

Rhodopsin =

scotopsin + 11-cis retinal

33

Rhodopsin + light --->

scotopsin +all-trans retinal

34

What is 11 cis retinal converted to?

all trans retinal and dissociates from scotopsin

35

What is metarhodopsin II?

an intermediate in this pathway that excites electrical changes in the rods

36

Bathorhodopsin (nsec)--->

lumirhodopsin

37

lumirhodopsin--->

metarhodopsin I

38

metarhodopsin I-->

metarhodopsin II

39

Metarhodopsin II--->

scotopsin or all trans retinal

40

scotopsin to

rhodopsin

41

all trans retinal to

11 cis retinal via isomerase orall trans retinol (vit A)

42

11 cis retinal to

rhodopsin

43

11 cis retinol to

11 cis retinal

44

all trans retinol vitamin A isomerase to

11 cis retinol-requires isomerase and metabolic energy

45

What does excitation of the rod cause?

Increased negativity of the intrarod membrane potential =hyperpolarization

46

What does decomposition of rhodopsin cause

decreases rod membrane conductance for Na ions in the outer segment

47

What does decomposition of rhodopsin result in?

hyperpolarization of entire rod membrane

48

What does the inner segment of the rod do?

continually pumps Na from inside rod to outside and K in opposite direction

49

How does K lead out of rod cell?

via non gated Channels

50

What kind of potential is created in the Rod cell

negative

51

Outer segment of rod in the dark

-membrane is leaky to Na ions that flow through cGMP-gated channels
-Na ions leak into cell and neutralize much of negativity on the inside of the entire cell
-under dark conditions, there is reduced electronegativity inside the membrane (-40 mV rather than the expected -70 to -80 mV

52

When rhodopsin is exposed to light?

it begins to decompose

53

The retinal portion of the rhodopsin complex is .... in the light?

activated and stimulated transducin (G protein)

54

What does transducin activate in the light?

cGMP phosphodiesterase

55

What does cGMP phosphodiesterase catalyze in the light?

cGMP ---> 5'GMP

56

What does reduction in cGMP cause in the light?

closure of Na channels

57

What happens to photoreceptors bc of closure of Na channels in the light?

become hyperpolarized

58

What happens when rhodopsin is activated in the light?

several hundred channels close for each rhodopsin molecule activated

59

How are cones different from rods?

the protein portions (opsins) of the photo-chemicals are different from the scotopsin in the rod photo-chemicals

60

What is the same in rods and cones?

retinal protions

61

What are cones sensitive to?

blue, green and red

62

What are the 5 layers of the retina?

photoreceptors
horizontal cells
bipolar cells
amacrine cells
ganglion cells

63

Photorecetpors include, transmit and synape?

include rods and conestransmit signals to outer plexiform layer synapse with bipolar cells and horzontal cells

64

plexiform layer is what?

layer of synaptic connections

65

What do the horizontal cells transmit signals from?

rods and cones to bipolar cells

66

What is another place horizontal cells transmit signals too?

outer plexiform layer

67

Horizontal cells output is?

always inhibitory (lateral inhibition)

68

Bipolar cells transmit signals from?

rods, cones, and horizontal cells

69

bipolar cells transmit signals to?

inner plexiform layer

70

bipolar cells synapse

with amacrine an ganglion cells

71

Amacrine cells transmit signals?

-directly from bipolar to ganglion cells-within inner plexiform layer from axons of bipolar cells to dendrites of ganglion cells or to other amacrine cells

72

ganglion cells transmit signals from?

retinal to brain

73

ganglion axons make up?

optic nerve

74

What is special about ganglion axons?

-only retina cells that transmit action signals-others use electronic conduction which allows graded conduction of signal strength

75

interplexiform cells transmit?

from inner plexiform layer to outer plexiform layer (retrograde)

76

interplexiform cells send

inhibitory signals-lateral inhibition

77

The foveal region has three neurons in direct pathway?

conesbipolar cellsganglion cells

78

What do pure rod vision consist of, four neurons?

rodsbipolar cellsamacrine cellsganglion cells

79

What is the neurotransmitters from rods and cones ---> bipolar cells

glutamate

80

what are the neurotransmitters for amacrine cells

eight or more kinds of neurotransmitters including GABA, glycine, dopamine, acetylcholine, indolamine (all inhibitory)

81

Amacrine cell that is a direct pathway for

rod conduction

82

amacrine cells that response strong to?

onset of continuing visual signal but fades rapidly

83

Some amacrine cells respond strongly at the offset of visual signals, but?

the response fades rapidly

84

Some amacrine cells respond when a light is?

turned off or on

85

some amacrine cells response to movement of a ?

spot across the retina in a specific direction

86

Most amacrine cells are interneurons that?

help analyze visual signals before they leave retina

87

What is the avg number of rods and cones on each ganglion cell?

60 rods and 2 cones converge on each ganglion cell and the optic nerve fiber from the ganglion cells

88

As ganglion cells approach the fovea, what happens?

fewer rods and cones converge on each optic fiber and rods and cones become more slender-increases visual acuity in central retinal-in central fovea there are only slender cones and no rods

89

What is the peripheral retina more sensitive to?

weak light-as many as 200 rods converge on a single optic fiber in the more peripheral regions of the retina

90

What are the types of ganglion cells?

WXY

91

What are W ganglion cells?

-make up about 40% of all ganglion cells - small-transmit signals 8 m/sec- receive most of their excitation from rods transmitted by way of small bipolar cells and amacrine cells-they have broad fields in the peripheral retina bc their dendrites spread widely in the inner plexiform layer

92

What are X ganglion cells?

-Make up about 55% of all ganglion cells-medium diameter-transmit signal 14 m/sex-they have small fields----signals represent discrete retinal locations

93

What does every X ganglion cell receive an input form?

at least on cone cell; therefore, probably responsible for all color vision

94

What are Y ganglion cells?

-make up about 5% of all ganglion cells-lg diameter ( up to 35 um)-transmit signals 50 msec or faster-response to rapid chagnes in visual image

95

What cells presumably apprise the CNS almost instantaneously when a new visual event occurs anywhere in the field without great accuracy with respect to location of field?

Y ganglion cells

96

The dorsal lateral geniculate nucleus relays info from optic tract to visual cortex by?

Way of optic radiation (geniculocalcarine tract)-high degree of spatial fidelity from retina to the visual cortex

97

What has 50% decussation in optic chiasm?

Dorsal lateral geniculate nucleus

98

What are the six nuclear layers in lateral geniculate nucleus?

II, III, V receive signals from lateral half of ipsilateral retinaI, IV, VI receive signals from medial half of opposite retina

99

What are layers I and II of the dorsal lateral geniculate nucleus?

magnocellular layers
contain lg neurons
receive input almost entirely from lg Y type ganglion cells
provides rapidly conduction pathway to visual cortex
transmits only black and white
point to point transmission is poor

100

What are layers III through VI of dorsal geniculate nucleus?

parvocellular layers
contain small to medium size neurons
receive input almost entirely from lg X type ganglion cells
provides moderate conduction pathway to visual cortex
transmit color
accurate pt to pt transmission

101

Lateal geniculate nucleus controls how much of the signal is?

allowed to pass to the cortex

102

source of gating control of the dorsal lateral geniculate nucleus

corticofugal fibers from primary visual cortex
reticular areas of the mesencephalon-both of these sources are inhibitory and help highlight visual information that is allowed to pass

103

The primary visual cortex is also called?

the striate cortex

104

Where is the primary visual cortex located?

occipital lobes

105

Where do signals from macular area terminate for the primary visual cortex?

terminate near the occipital pole

106

Where do signals from the more peripheral retina terminate for the primary visual cortex?

at or in concentric half circles anterior to the ole but still along the calcarine fissure

107

How many distinct layers does the primary visual cortex have?

six

108

Where does geniculocalcarine fibers terminate?

mainly in layer IV of the primary visual cortex

109

Layer IV is organized into what for the primary visual cortex?

signals from Y ganglion cells terminate in layer IV c,alphasignals from X ganglion cells terminate in layer IV c beta and IVa

110

The visual cortex is organized into several million?

vertical columns of neuronsdiameter = 30 to 50 um=1000 neurons per column

111

Where are special column like areas called color blobs located?

among the columns of the secondary visual areas-receive lateral signals from adjacent visual columns and are activated specifically by color signals

112

The signals from the two separate eyes enter?

alternating stripes of columns in layer IV

113

What does the cortical area decipher?

whether the respective areas of the two visual images from the two separate eyes are in register w each other

114

How is the deciphered information from the cortical areas used?

to adjust the directional gaze of the separate eyes-this is also required for stereopsis

115

When does the lens assume an almost spherical shape?

when the lens is in a relaxed state with no tension on its capsule

116

What do the suspensory ligaments attached radially around the lens create?

a tension that causes the lens to remain relatively flat under normal eye conditions

117

What doe meridional fibers of ciliary muscles do?

contract and release tension on lens

118

What CN controsl both sets of ciliary muscles?

CN III

119

What are accommodations to the eye that come with age?

Lens becomes larger and thicker w agelens becomes less elastic w agepower of accommodation decreases to less than 2 diopters by the age of 45 to 50it decreases to 0 by the age of 70presbyopia