Visual System Flashcards Preview

DPT704: Neuro Hank > Visual System > Flashcards

Flashcards in Visual System Deck (135):
1

What is the optic disk?

exit of the CNII Optic Nerve

2

What does the optic disk produce?

a "blind spot"

3

What does the macula lutea contain?

central fovea (pit)

4

What are the four cell layers of the retina?

1. Pigment Layer
2 and 3. Layer of Rods and Cones
4. Ganglion Cell Layer

5

What is the pigment layer derived from?

choroid

6

What does the pigment cell layer attach to the eyeball?

retina

7

What is the function of the pigment cell layer?

absorbs stray light

8

What is the funcion of the layer of rods and cones?

light receptors

9

Where are rods located?

periphery of retina

10

What is the function of rods?

for low light vision and perception of movement

11

Where are the cones located?

concentrated in central retina

12

Does the fovea contain only rods or cones?

cones

13

What is the significance of the fovea?

area of maximum visual acuity, color and brightness discrimination.

14

mylenated axons of the ganglion cell layer for what?

CNII Optic Nerve

15

Ganglion cells describe

receptive fields

16

In the normal eye, how is the orientation of the object focused on the retina?

inverted

17

What is light refracted by in the eye?

cornea, aqueous humor, lens, and vitreous humor

18

What is the function of the lens?

The lens is a device for changing the refractive power. Changes in refractive power are accomplished by changing the shape of the lens.

19

The lens is made ___ for close viewing, and ___ for distant viewing.

Rounder for close viewing and flatter for distant viewing.

20

The change in refractive power which allows the viewing of near objects is called ___

accomodation

21

To view a near object, the lens must increase its refractive power by becoming more

convex (rounder)

22

At rest, the lens is held in a relatively ___ shape

flat

23

At rest the lens is held in a relatively flat shape by the

suspensory fibers that connect it to the ciliary muscle.

24

To accomodate for near vision, the ciliary muscle ___

contracts reducing tension on the suspensory fibers

25

Due to the lens' natural elasticity, it contracts to a more ___ shape.

spherical

26

Contraction of the ciliary muscles is controlled by

parasmypathetic nervie fibers

27

What is Emmetropia?

the normally occurring condition in which the image of an object is focused on the retinal surface.

28

What is Hypermetropia?

(far-sightnedness) - the focal point falls behind the retinal surface.

29

What is Myopia?

(near-sightnedness) - the focal point falls in front of the retina

30

What is Presbyopia?

is the loss of lens elasticity with age

31

What is the function of bifocals?

part of the lens that corrects for distance and a part that corrects for near vision due to loss of lens elasticity with age.

32

What are the two types of photoreceptors?

1. Rods
2. Cones

33

Is excitation threshold low or high for rods?

low excitation threshold

34

Are rods used in dim or high light conditions?

dim conditions (low excitation threshold)

35

Is rod acuity poor or high?

Poor

36

Why doesn't it matter that rod acuity is poor?

because when light is low, you can't see small objects anyway.

37

Is excitation threshold low or high for cones?

high

38

Are cones used in dim or high light conditions?

high light (high excitation threshold

39

Is cone acuity low or high?

Acuity is high

40

Do rods or cones provide color vision?

cones

41

What is the ability to distinguish color due to?

the presence of three separate cone populations, each of which is maximally sensitive to different wavelength of light: blue, green, and red.

42

What is perception of other colors due to?

relative excitation of the different populations of cones.

43

What is colorblindness due to?

absence of one or more of the cone populations

44

For neural coding of visual signals, generator potentials originating in receptors are transmitted to what type of cell?

bipolar cells

45

For neural coding of visual signals, generator potentials originating in receptors are transmitted to bipolar cells and then

altered by other cells in the retina

46

What are the two separate systems in which the neural coding of visual signals can be visualized?

Vertical System
Horizontal System

47

What is the Vertical System for neural coding of visual signals?

signals pass from receptor to bipolar cells to ganglion cells

48

What is the Horizontal System for neural coding of visual signals

horizontal and amicrine cells provide lateral interactions (lateral inhibition) between the different vertical system components

49

What is the function of ganglion cells?

Ganglion cells are the final stage of retinal processing, and tasmit information to subcortical visual centers in the brain?

50

Axons of ganglion cells form the

optic nerve

51

Receptive Field Definition

the receptive field (RF) of a ganglion cell is defined as that area in visual space (or the corresponding area of retinal surface, which upon illumination, influences the signaling of that neuron.

52

How have ganglion cells been subdivided?

on the basis of their response duration or morphology.

53

What are "sustained" ganglion cells?

cells that respond as long as the stimulus remains within the receptive field.

54

What are "transient" ganglion cells?

cells that respond only when the light it turned on of off

55

P-cells are (SMALL/LARGE) ganglion cells of the (TRANSIENT/SUSTAINED) type

small ganglion cells of the sustained type

56

M-cells are (SMALL/LARGE) ganglion cells of the (TRANSIENT/SUSTAINED) type

large ganglion cells of the transient type

57

At present it is believed that M-cells are primarily concerned with

signaling changes in the scene being viewed including movement

and changes in light and dark contrast and with basic form analysis

58

P-cell provide information about

fine detail (high resolution analysis of image)

and color.

59

Information that is transmitted from the eye through the optic nerve must eventually reach ___ the to be perceived.

cortex

60

Each point on the retinal surface sees a particular point in the visual field, with neighboring retinal points seeing neighboring visual filed points. Thus the visual field is represented on a corresponding are on the

retina (retinal field) with topographical representation being maintained throughout the rest of the visual system.

61

The visual field can be divided by a vertical line at the fixation point into a

left and right hemifield

62

Each half of the brain receives information from (IPSILATERA/CONTRALTERAL/BILATERAL) hemifield.

Each half of the brain receives information only from the opposite (CONTRALTERAL) hemifield.

63

The separation of the brain receiving information from only the opposite (contralteral) hemifield happens at the level of the ___

optic chiasm

64

Define homonymity

Images of the visual world are composed of information from the two eyes (binocular) which are merged to form a single image.

65

What is the general definition of Homonymous? As the term applied to the visual fields?

corresponding halves. This term as it applies to the visual fields, describes both eyes viewing the same or corresponding visual field.

66

Define Contralteral homonymous perception

The right primary visual cortex (area 17) is perceiving only the left half of the visual field.

67

The visual pathway organization is such that everything (CAUDAL/ROSTRAL) to the optic chiasm is carrying only contralteral homonymouse perception

The visual pathway organization is such that everything CAUDAL to the optic chiasm is carrying only contralteral homonymouse perception

68

Define anopia

loss of visual perception

69

Define hemianopia

loss of visual perception of half of the entire visual field

70

What is the general definition of Heteronymous? As the term applies to the visual fields?

different halves. As it applies to visual fields, describes each eye viewing different visual fields.

71

Define Binasal Heteronymous Hemianopia or Binasal Hemianopia.

When each eye is only able to see the ipsilateral temporal visual field and not the nasal visual fields.

72

Optic nerve fibers from temporal retina (nasal visaul hemifield) course caudally along the ___ edge of the optic nerve, optic chiasm, and optic tract

caudally along the LATERAL edge

73

Optic nerve fibers from the temporal retina (nasal visual hemifield) course (IPSILATERA/CONTRALTERAL/BILATERAL) to the lateral geniculate nucleus (LGN).

Optic nerve fibers from the temporal retina (nasal visual hemifield) course to the to the IPSILATERAL lateral geniculate nucleus (LGN).

74

Optic nerve fibers from nasal retina (temporal visual hemifield) course caudally along the ___ edge of the optic nerve

caudally along the MEDIAL edge

75

Optic nerve fibers from the nasal retina (temporal visual hemifield) course (IPSILATERA/CONTRALTERAL/BILATERAL) to the lateral geniculate nucleus (LGN).

Optic nerve fibers from the nasal retina (temporal visual hemifield) course to the to the CONTRALATERAL lateral geniculate nucleus (LGN).

76

Optic fibers from the nasal retina (temporal visual hemifield) course caudally along the medial edge of the optic nerve and then

cross in the chaism and then course along the medial edge of the optic tract

77

Optic fibers from the upper retina (inferior or lower visual hemifield) course caudally along the ___ edge of the edge optic nerve, optic chiasm, optic tract.

dorsal

78

Optic fibers from the lower retina (superior or lower visual hemifield) course caudally along the ___ edge of this retinogeniculate pathway.

ventral

79

Retinogeniculate fibers carrying information from the more peripheral visual fields are located more

superficially within the optic nerve, optic chiasm, and optic tract.

80

Retinogeniculate fibers carrying information from the central (fovea) visual fields are located more

internally within the optic nerve, optic chiasm, and optic tract.

81

After optic nerve fibers pass through the chiasm they continue as the

optic tract

82

After optic nerve fibers pass through the chiasm they continue as the optic tract to end primarily (80%) in the ___ with some (20%) terminating in the ___.

After optic nerve fibers pass through the chiasm they continue as the optic tract to end primarily (80%) in the LGN with some (20%) terminating in the MIDBRAIN IN OR NEAR THE SUPERIOR COLLICULUS.

83

Optic nerve fibers reach the midbrain via the

brachium of the superior colliculus (BSC)

84

After very specific synapses in the LGN, thalamocortical axons proceed to

primary visual cortex (area 17, calcarine cortex)

85

After very specific synapses in the LGN, thalamocortical axons proceed to primary visual cortex (area 17, calcarine cortex) by way of

visual radiations (geniculocalcarine radiation, optic radiations)

86

geniculocalcarine fibers that are carrying visuotopic information from the upper halves of both retinae (lower visual hemifields) course ___ to reach the ___.

course directly backward around the lateral ventricle as part of the internal capsule to reach the superior bank of the calcarine fissure - CUNEUS

87

geniculocalcarine fibers that are carrying visuotopic information from the lower halves of the retinae (upper visual hemifields) course

forward toward the tip of the tempooral horn of the lateral ventricle, then loop inferiorly then caudally in the temporal lobe to reach the inferior bank of the calcarine fissure - lingual gyrus.

88

What is Meyer's Loop?

long loop of geniculocalcarine fibers carrying visuotopic information from the lower halves of the retinae (upper visual hemifields)

89

What is Contralateral Upper Homonymous Quadrantanopia?

damage to meyers loop - affects the contralateral upper quadrant of the whole visual field.

90

What part of the visual field does the right cuneus contain?

contralateral (left) lower quadrant from both eyes

(right temporal upper eye and left nasal upper eye)

91

What part of the visual field does the left lingual gyrus contain?

contralateral (right) upper quadrant from both eyes

(left nasal upper eye and right temporal upper eye)

92

Where is the Lateral Geniculate Nucleus (LGN) located?

at the termination of the optic tracts (retinogeniculate fibers) in the thalamus

93

How many layers is the LGN composed of in the human?

six

94

Each LGN contains a representation of

the contralateral visual hemifield (topography)

95

The six layers of the LGN are divided into two groups:

1. Magnocellular Layers
2. Parvocellular Layers

96

Cells in the magnocellular layer are involved in the perception of

dark and light contrast (M-cells, correspond to information from transient ganglion cells that are activated by rods)

97

Cells in the parvocellular layers process

fine spatial and color information (P-cells, correspond to information from sustained ganglion cells that are activated by cones.

98

Axons of retinal ganglion cells project to several areas within the midbrain, with the major projection being to the

superior colliculus

99

the reinocollicular fibers travel through the

brachium of the superior colliculus

100

the reinocollicular fibers travel through the brachium of the superior colliculus to terminate in the

superior colliculus

101

From the superior colliculus, post-synaptic fibers project to the

prestriate visual areas that surround primary visual cortex (Areas 18 and 19)

102

A small bundle of fibers branches off in the brachium of the superior colliculus and terminates in the

nuclei of the pretectal area just rostral to the superior colliculus.

103

A small bundle of fibers branches off in the brachium of the superior colliculus and terminates in the nuclei of the pretectal area just rostral to the superior colliculus. This connection is the afferent limb of the

pupillary light reflex that adjusts pupil diameter specific to amount of light entering the eye.

104

connections to the oculomotor complex result in

constrinction of pupil

105

descending connection to T1,T2 intermediolateral cell column control

dialation of pupil

106

This type of defect is often first clue to some pathology in "silent" areas of cortex, especially temporal lobe cortex

quadrant defects

107

Define macular sparing

field defects which include everything EXCEPT macular field (central vision)

108

When does macular sparing occur?

when entire ipsilateral visual cortex is destroyed except for the occipital pole. The occipital pole (foveal representation) receives an overlapping blood supply.

109

Two areas of the cortex that respond to visual stimulation

primary visual (striate) cortex or area 17
secondary and tertiary visual (prestriate) cortex or areas 18 and 19

110

____ visual field is represented on the posterior pole of the occipital lobe

central visual field

111

____ are represented in the more anterior portions of the calcarine suclus

peripheral visual fields

112

the ____ representation is greatly maginified and occupies a disproportionately larger portion of the cortical tissue.

foveal

113

The information is then distributed through areas 18 and 19 (V2, V3) and then to areas in the temporal lobe for

object recognition

114

The information is then distributed through areas 18 and 19 (V2, V3) and then to areas in the posterior parietal lobe for

perception of motion, rotation ad dpeth

115

The information is then distributed through areas 18 and 19 (V2, V3) and then to areas in the parieto-temporal lobe junction for

perception of color and to a lesser extent motion, rotation and depth.

116

The temporal lobe, posterior parietal lobe, and parito-temporal lobe junction are extensively interconnected to allow us to perceive

visual space (depth and movement) along with object specificity (color and form) within the visual space.

117

The information derived from p-cells of LGN is responsible for relaying _____ to the temporal lobe regions (P pathway).

information on form and color of objects

118

The information derived from m-cells of LGN is reponsible for relaying ____ to parietal areas (M pathway).

information concerning gross form and motion

119

Depending on location and extent, a lesion in the Primary Visual cortex area 17 results in

contralateral visual deficits (visual field cut)

120

If a lesion involves all of area 17 bilaterally,

the subject will appear blind, however under special test conditions, some limited visual capabilities are demonstratabe, such as the pupillary light reflex.

121

Prestriate (Extrastriate) Cortex (areas 18 and 19) called visual association cortex perceives projections from three sources:

-ipsilateral primary visual cortex
-ipsilateral superior colliculus
-contralateral prestriate cortex

122

Lesions to the prestriate (extrastriate) cortex (areas 18 and 19)

are not devastating as those to area 17, and cause deficits in discriminating between objects or patterns.

123

The posterior half of the middle and inferior temporal gyri receives

projections from prestriate cortex and superior colliculus.

124

The cells in the the posterior half of the middle and inferior temporal gyri have ____ when compared to stiriate and prestriate cortex.

very large receptive fields

125

The receptive fields of the cells in the posterior half of the middle and inferior temporal gyri may extend across the mindline and thus,

the cell is responsive to stimuli from both hemifields

126

Because the receptive fields of the cells in the posterior half of the middle and inferior temporal gyri may extend across the midline, the cell is responsive to stimuli from both hemifields. This indicates

a convergence of information from both hemispheres into this cortical region (i.e. it receives a projection from the contralateral hemisphere).

127

What is the main sinificance of the posterior half of the middle and inferior temporal gyri?

This is the first level of the visual system in which visual stimuli from both hemispheres are merged to form a single image.

128

Animals with bilateral leasions to the posterior half of the middle and inferior temporal gyri have

considerable difficulty in identifying the salient features of objects or patterns that distinguish them.

129

The posterior part of the temporal lobe and its junction with the inferior parietal lobe (area V5 - P-pathway), including parts of the superior temporal sulcus is involved in

form and color recognition.

A part of this region is also involved in movement, especially with respect to transnational movements.

130

The anterior half of the middle and inferior temporal gyri, broadmann's areas 20 and 21, receives

projections from the posterior half of these gyri (p pathway)

131

The physiological properties of the cells found within the anterior half of the middle and inferior temporal gyri, broadmann's areas 20 and 21, are similar to thouse found in the

posterior area, especially form of objects.

132

Animals with lesions to the anterior half of the middle and inferior temporal gyri, broadmann's areas 20 and 21, are greatly impaired in

their ability to recognize a previously seen pattern or object.

133

Because the anterior half of the middle and inferior temporal gyri, broadmann's areas 20 and 21, experiences lesions impaires ability to recognize a perviously seen pattern or object, this are has been suggested to function in

"memorizing" a visual pattern (object recognition)

134

The posterior parietal love, area V3 (Broadmann's area 7) receives

projections from visual association areas (M pathway).

135

The posterior parietal love, area V3 (Broadmann's area 7) is involved in the ability to

identify rotational and directional movements.

It is also involved in the ability to identify visual spatial orientation, or position of body in space (depth perception)