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Physiology > Vision > Flashcards

Vision Flashcards

1
Q

Special senses are…

A

confined to special sensory organs in the head

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2
Q

Eye and vision are the…

A

dominant sense in humans and most mammals

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3
Q

Visual system detects and interprets…

A

photic stimuli (visible light)

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4
Q

Visible light are electromagnetic waves between…

A

400 and 750 nm long

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5
Q

Eye is made up of…

A
  • optical portion

- neural component

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6
Q

Optical portion focuses…

A

visual image onto receptor cells

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7
Q

Neural components:

A

transduce visual image into a pattern of neural discharges

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8
Q

Retina:

A

neural component and innermost tunic of wall in the eye

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9
Q

Retina has 5 types of neuronal cells:

A
  • photoreceptors
  • bipolar cells
  • horizontal cells
  • amacrine cells
  • ganglion cells
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10
Q

Retina has a _____ of the visual signal from ______

A

convergence, photoreceptors to ganglion cells

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11
Q

Two types of photoreceptors:

A
  • rods

- cones

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12
Q

Photoreceptors are attached to…

A

pigmented epithelium

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13
Q

Photoreceptors receive nutrients by…

A

diffusion from choroid

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14
Q

Function of photoreceptors:

A

transduce light to electrical signals

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15
Q

W/out light, photoreceptors…

A

release glutamate (excitatory neurotransmitters)

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16
Q

W/ light, photoreceptors…

A

undergo hyperpolarization and release of neurotransmitters are inhibited

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17
Q

Location of rods:

A

everywhere but optic disc and fovea

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18
Q

Rods:

A
  • very sensitive
  • best under reduced lighting
  • responds to large range of light intensities
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19
Q

Type of images/vision that rods provide:

A
  • night (scotopic) vision
  • crude vision (low light discrimination of objects)
  • black and white only
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20
Q

Rods have a ______ field

A

large receptive field that allow peripheral detection of movement

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21
Q

Loss of rod function leads to…

A

night blindness

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22
Q

Optic discs are…

A

axons of ganglion cells

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23
Q

Cones are only found in…

A

macula lutea and fovea centralis

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24
Q

Fovea centralis is the…

A

sharpest point of vision

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25
Q

Cones are only active at…

A

higher light levels

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26
Q

Cones provide…

A
  • day (photopic) vision

- color discrimination

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27
Q

T/F: there are maximum convergence at cones

A

F, minimal convergence

- allows for sharp and detailed vision

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28
Q

Loss of all cone function leads to…

A

blindness

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29
Q

Color blindness is linked to…

A
  • X gene deficit

- loss of one or more cone type

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30
Q

Functional anatomy of rods and cones:

A
  • outer segment
  • inner segment
  • synaptic zone
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31
Q

Outer segment of rods and cones have:

A
  • photo-sensitive transmembrane pigments absorb light rays

- leaky Na+ channels: intracellular messenger of cGMP gated channels

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32
Q

Outer segment of rods specifically have:

A
  • rhodopsin (visual purple)
  • 11 cis-retinal
  • protein scotopsin
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33
Q

Outer segment of cones specifically have:

A
  • blue, green, and red sensitive pigments
  • 11 cis-retinal
  • protein photopsin
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34
Q

Inner segment of rods and cones have:

A
  • nucleus
  • high [Na+/K+ ATPase pumps]
  • lots of mitochondria
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35
Q

Synaptic zone of rods and cones have:

A
  • VG Ca2+ channels

- vesicles w/ glutamate (excitatory neurotransmitter)

36
Q

In absence of light, the retina…

A
  • rhodopsin is intact (11 cis-retinal+opsin protein)
  • membrane potential of photoreceptors: -40 mV
    1. leaky Na+ channels open
    2. VG Ca2+ channels open
    3. steady release of glutamate
37
Q

When exposed to light, the retina…

A
  1. rhodopsin absorbs photon
  2. conformational change initiated
  3. activates G-protein: G1 transducin
  4. Na+ channels close
  5. VG Ca2+ close
38
Q

What happens when conformational change is initiated during the exposure to light?

A
  • 11-cis-retinal changes to all trans retinal

- all trans retinal and opsin completely dissociates

39
Q

Activation of G protein when retina is exposed to light leads to…

A
  • the activation of cGMP phosphodiesterase

- cGMP gets converted to inactive 5’GMP

40
Q

What happens when Na+ channels close during the exposure of light of retina?

A
  • Na+/K+ ATPase pumps continues

- hyperpolarizes cell to -70 to -80 mV

41
Q

What happens when VG Ca2+ channels close during the exposure of light of retina?

A

glutamate is prevented from being released

42
Q

Recovery process of the retina:

A
  • all trans retinal reconverted to 11-cis-retinal by isomerase enzyme
  • reconverted 11-cis-retinal spontaneously recombines w/ opsin protein
  • rhodopsin kinase
43
Q

Rhodopsin kinase:

A

inactivates the activated rhodopsin

44
Q

Vitamin A (all-trans retinol):

A

storage form for 11-cis-retinol

45
Q

Night blindness is a result of…

A

a severe deficiency of vitamin A

46
Q

Types of pathways of signal w/in the retina:

A
  • direct pathway

- indirect pathway

47
Q

Direct pathway:

A
  • photoreceptor -> bipolar cell -> ganglion cell

- cone -> bipolar -> ganglion cell (fovea)

48
Q

Indirect pathway:

A
  • signal is modified along the pathway

- horizontal and amacrine cells

49
Q

Types of bipolar cells:

A

excitatory or inhibitory

- depends on neurotransmitters released

50
Q

Excitatory bipolar cells:

A
  • depolarizes in response to glutamate
  • direct excitation from rods/cones
  • increases the frequency of ganglionic cell signals
  • opens cation channels
51
Q

Inhibitory bipolar cells:

A
  • hyperpolarize in response to glutamate
  • receives signal indirectly through horizontal cell
  • decreases the frequency of ganglionic cell signals
  • closes cation channels
52
Q

Horizontal cells:

A
  • part of indirect pathway
  • output is always inhibitory (hyperpolarizing)
  • provides lateral inhibition
  • prevents spill-over effects of neurotransmitters
53
Q

Amacrine cells:

A
  • part of indirect pathway
  • starts integration of visual signals
  • starts to analyze signals
  • depolarizing
54
Q

Ganglion cells:

A
  • only cells in retina that exhibit true all or nothing potential
  • continuously fires AP’s
  • rates are modified by photoreceptor inputs
  • convergence determines the response of ganglion cells
55
Q

Ganglion cells throughout the retina differ in:

A
  • size of receptive fields
  • proportion of rods/cones
  • speed of conduction (axon diameter)
56
Q

Ganglion cells have 2 basic patterns of receptive fields:

A
  • on center/off surround

- off center/on surround

57
Q

The 2 basic patterns of receptive fields are classified based on…

A

rate of AP output in response to light in center of field

58
Q

Ganglion has three cell types:

A
  • W
  • X
  • Y
59
Q

W ganglion cells transmit…

A

rod vision

60
Q

X ganglion cells transmit…

A
  • visual image and color

- color analysis occurs in the retina

61
Q

When x ganglion cells are stimulated by red, green, and blue cones…

A

white is seen

62
Q

When x ganglion cells are stimulated by one cone color…

A

the other cone color inhibits it

63
Q

Y ganglion cells transmit…

A

instantaneous changes in visual image

64
Q

Visual pathway from retina to brain:

A
  1. myelinated axons of ganglion cells leave eye as optic nerve
  2. optic nerves meet at optic chiasma, but don’t synapse
  3. ganglion cell axons leave optic chiasma through optic tracts
  4. travels to primary visual cortex in occipital lobe
  5. travels to secondary visual cortex
65
Q

Optic disc is where the ____ passes through the retina

A

optic nerve

- “blind spot” in visual field

66
Q

At the optic chiasma, fibers from the nasal halves of the retina…

A

cross over

67
Q

Fibers from the nasal halves of the retina carry info from…

A

temporal portions of visual fields

68
Q

At the optic chiasma, fibers from the temporal halves of the retina…

A

stay on the side of origin

69
Q

Fibers from the temporal halves of the retina carry info from…

A

nasal portions of visual fields

70
Q

Optic tracts have two types of ganglion cells:

A
  • magnocellular ganglion cells

- parvocellular ganglion cells

71
Q

Magnocellular ganglion cells control…

A

movement

72
Q

Parvocellular ganglion cells control…

A

fine detail

73
Q

Ganglion cell axons in the optic tracts synapse in the…

A

lateral geniculate nucleus

74
Q

Optic radiations synapse in the…

A

primary visual cortex

75
Q

In the primary visual cortex, there is a large representation for…

A

fovea

76
Q

Primary visual cortex is organized into…

A

columns

- specific to right/left eye

77
Q

Lateral geniculate nucleus:

A

specific area for visual information

  • highly mapped
  • gates transmission
78
Q

Output from lateral geniculate nucleus goes through…

A

optic radiations

79
Q

Three types of columns in the primary visual cortex:

A
  • simple cells
  • complex cells
  • rando ones: provide color information
80
Q

Columns with simple cells respond to…

A
  • bars of light
  • lines
  • edges in specific orientation
81
Q

Columns with complex cells respond to…

A

linear/angular objects moving laterally across visual field

82
Q

Secondary visual cortex:

A

analyzes information from primary visual cortex

- sends to association areas for identification

83
Q

Secondary visual cortex is made up of…

A

stereopsis, which helps with binocular depth perception

84
Q

Damage to any area in the visual pathway can lead to…

A

visual field defects

85
Q

Pituitary tumor can compress fibers at optic chiasm, which causes…

A

tunnel vision

86
Q

Lesions in secondary visual cortices causes…

A

visual agnosia: inability to recognize faces of friends, familiar objects, or colors

Physiology (33 decks)

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