Physiology > Vision > Flashcards

Vision Flashcards

(86 cards)

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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
Cones are only active at...
higher light levels
26
Cones provide...
- day (photopic) vision | - color discrimination
27
T/F: there are maximum convergence at cones
F, minimal convergence | - allows for sharp and detailed vision
28
Loss of all cone function leads to...
blindness
29
Color blindness is linked to...
- X gene deficit | - loss of one or more cone type
30
Functional anatomy of rods and cones:
- outer segment - inner segment - synaptic zone
31
Outer segment of rods and cones have:
- photo-sensitive transmembrane pigments absorb light rays | - leaky Na+ channels: intracellular messenger of cGMP gated channels
32
Outer segment of rods specifically have:
- rhodopsin (visual purple) - 11 cis-retinal - protein scotopsin
33
Outer segment of cones specifically have:
- blue, green, and red sensitive pigments - 11 cis-retinal - protein photopsin
34
Inner segment of rods and cones have:
- nucleus - high [Na+/K+ ATPase pumps] - lots of mitochondria
35
Synaptic zone of rods and cones have:
- VG Ca2+ channels | - vesicles w/ glutamate (excitatory neurotransmitter)
36
In absence of light, the retina...
- 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
When exposed to light, the retina...
1. rhodopsin absorbs photon 2. conformational change initiated 3. activates G-protein: G1 transducin 4. Na+ channels close 5. VG Ca2+ close
38
What happens when conformational change is initiated during the exposure to light?
- 11-cis-retinal changes to all trans retinal | - all trans retinal and opsin completely dissociates
39
Activation of G protein when retina is exposed to light leads to...
- the activation of cGMP phosphodiesterase | - cGMP gets converted to inactive 5'GMP
40
What happens when Na+ channels close during the exposure of light of retina?
- Na+/K+ ATPase pumps continues | - hyperpolarizes cell to -70 to -80 mV
41
What happens when VG Ca2+ channels close during the exposure of light of retina?
glutamate is prevented from being released
42
Recovery process of the retina:
- all trans retinal reconverted to 11-cis-retinal by isomerase enzyme - reconverted 11-cis-retinal spontaneously recombines w/ opsin protein - rhodopsin kinase
43
Rhodopsin kinase:
inactivates the activated rhodopsin
44
Vitamin A (all-trans retinol):
storage form for 11-cis-retinol
45
Night blindness is a result of...
a severe deficiency of vitamin A
46
Types of pathways of signal w/in the retina:
- direct pathway | - indirect pathway
47
Direct pathway:
- photoreceptor -> bipolar cell -> ganglion cell | - cone -> bipolar -> ganglion cell (fovea)
48
Indirect pathway:
- signal is modified along the pathway | - horizontal and amacrine cells
49
Types of bipolar cells:
excitatory or inhibitory | - depends on neurotransmitters released
50
Excitatory bipolar cells:
- depolarizes in response to glutamate - direct excitation from rods/cones - increases the frequency of ganglionic cell signals - opens cation channels
51
Inhibitory bipolar cells:
- hyperpolarize in response to glutamate - receives signal indirectly through horizontal cell - decreases the frequency of ganglionic cell signals - closes cation channels
52
Horizontal cells:
- part of indirect pathway - output is always inhibitory (hyperpolarizing) - provides lateral inhibition - prevents spill-over effects of neurotransmitters
53
Amacrine cells:
- part of indirect pathway - starts integration of visual signals - starts to analyze signals - depolarizing
54
Ganglion cells:
- 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
Ganglion cells throughout the retina differ in:
- size of receptive fields - proportion of rods/cones - speed of conduction (axon diameter)
56
Ganglion cells have 2 basic patterns of receptive fields:
- on center/off surround | - off center/on surround
57
The 2 basic patterns of receptive fields are classified based on...
rate of AP output in response to light in center of field
58
Ganglion has three cell types:
- W - X - Y
59
W ganglion cells transmit...
rod vision
60
X ganglion cells transmit...
- visual image and color | - color analysis occurs in the retina
61
When x ganglion cells are stimulated by red, green, and blue cones...
white is seen
62
When x ganglion cells are stimulated by one cone color...
the other cone color inhibits it
63
Y ganglion cells transmit...
instantaneous changes in visual image
64
Visual pathway from retina to brain:
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
Optic disc is where the ____ passes through the retina
optic nerve | - "blind spot" in visual field
66
At the optic chiasma, fibers from the nasal halves of the retina...
cross over
67
Fibers from the nasal halves of the retina carry info from...
temporal portions of visual fields
68
At the optic chiasma, fibers from the temporal halves of the retina...
stay on the side of origin
69
Fibers from the temporal halves of the retina carry info from...
nasal portions of visual fields
70
Optic tracts have two types of ganglion cells:
- magnocellular ganglion cells | - parvocellular ganglion cells
71
Magnocellular ganglion cells control...
movement
72
Parvocellular ganglion cells control...
fine detail
73
Ganglion cell axons in the optic tracts synapse in the...
lateral geniculate nucleus
74
Optic radiations synapse in the...
primary visual cortex
75
In the primary visual cortex, there is a large representation for...
fovea
76
Primary visual cortex is organized into...
columns | - specific to right/left eye
77
Lateral geniculate nucleus:
specific area for visual information - highly mapped - gates transmission
78
Output from lateral geniculate nucleus goes through...
optic radiations
79
Three types of columns in the primary visual cortex:
- simple cells - complex cells - rando ones: provide color information
80
Columns with simple cells respond to...
- bars of light - lines - edges in specific orientation
81
Columns with complex cells respond to...
linear/angular objects moving laterally across visual field
82
Secondary visual cortex:
analyzes information from primary visual cortex | - sends to association areas for identification
83
Secondary visual cortex is made up of...
stereopsis, which helps with binocular depth perception
84
Damage to any area in the visual pathway can lead to...
visual field defects
85
Pituitary tumor can compress fibers at optic chiasm, which causes...
tunnel vision
86
Lesions in secondary visual cortices causes...
visual agnosia: inability to recognize faces of friends, familiar objects, or colors
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