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CNS > Unit 8 - Vision Physiology > Flashcards

Unit 8 - Vision Physiology Flashcards

1
Q

Colour of melanin

A

Brown

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2
Q

Vascularisation of iris

A

Highly vascularised

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3
Q

What cells are found near the iris SM

A

Pin cells

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4
Q

Overview of structures of eye

A
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5
Q

Where do we try and aim for light to hit

A

Fovea - centre of macula

Highest acuity - photoreceptors are packed in this region - (blindness called macular degeneration)

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6
Q

Function of outer layers of eye

A

Protective

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7
Q

What structures change the shape of the lens

A

Ciliary bodies

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8
Q

What structures absorb light

A

Pigmentation (melanin) in the choroid layer absorb light

Albinos have poor eyesight due to low levels of melanin (pink irises)

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9
Q

Accomodation by lens

A

Capacity to focus light on the retina

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10
Q

RODS

Vision type

Acuity

Adaptation

Number of rods in the eyes

A
  • Responsible for night vision
  • Very sensitive to light - low threshold so high level of photopigment
  • Low acuity - much amplification of signal, convergence and summation of signal at bipolar cells
  • Adapt slowly (summation in 100ms)
  • 100 million rods but less dense at fovea
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11
Q

CONES

Type of vision

Sensitivity (hence threshold)

Acuity

Different types

Region cones are found in

Resolution

A
  • Less sensitive ⇒ high threshold
  • High acuity - less signal amplification, little convergence
  • Concentrated in fovea (macula region - 3 million in each eye)
  • 3 types - red, green, blue
  • High temporal resolution (adapt early)
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12
Q

Change in MP as a result of light hitting rods & cones

A

Hyperpolarisation

Graded response

RMP is higher than in other cells

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13
Q

Structure of rod vs cone

A
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14
Q

Where do rods & cones lie in the retina

A

Choroid plexus lies beneath

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15
Q

What is present in higher conc in rods

A

Photopigment

⇒ more sensitive to light

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16
Q

Pigment present in the eyes

A

Rhodopsin (opsin + retinal)

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17
Q

Retinal isoforms

How is 1 changed to the other

A

11-cis retinal - non-activated rhodopsin

All-trans retinal - activated

Light alters shape of retinal molecule to trans

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18
Q

Which retinal isoform is activated

A

All-trans retinal

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19
Q

Chain of events once 11-cis retinal → all-trans retinal

A

Opsin and retinal split // metarhodopsin II (activated rhodopsin)

Excites electrical change in photoreceptors

Rods and different cones contain different isoforms of opsin

Varied absorption characteristics

Scotopsin (rods), photopsins (cones)

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20
Q

Scotopsin

A

Rods

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21
Q

Photopsins

A

Cones

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22
Q

What is retinal a derivative of

A

Vitamin A (carrots)

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23
Q

Prevalence of colour blindness among males vs females

A

8% males

0.5% females

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24
Q

Categories of photopsins

A

S (blue) 420 nm

M (green) 540 nm

L (red) 570 nm

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25
What opsins are X linked
M & L Constitute 90-95% of opsins
26
M cone and colour blindness
75% of colour blindness cases
27
Normal (trichromat)
28
Protanopia
29
Deuteranopia
30
S photopsin
blue 420 nm
31
M photopsin
green 540 nm
32
L photopsin
red 570 nm
33
MOA of dark current (happens in the dark)
Influx of Na+ Depolarisation Membrane potential = -40 mV cGMP splits Na+ channels open
34
Effect of activation of photopigment
Reduces cGMP levels (NB light causes hyperpolarisation) GTP → cGMP → 5'GMP (INACTIVE) GTP → cGMP // guanylyl cyclase cGMP → 5'GMP // cGMP phosphodiesterase
35
Enzymes involved in metabolism of GTP
GTP → cGMP // guanylyl cyclase cGMP → 5'GMP // cGMP phosphodiesterase
36
Function of cGMP How is this affected by splitting of opsin and retinal
Opsin and retinal are split - metarhodopsin II created This leads to **LOWERING of levels of cGMP because metarhodopsin II activates cGMP phosphodiesterase** (NB - cGMP → 5'GMP // cGMP phosphodiesterase)
37
How does metarhodopsin II activate cGMP phosphodiesterase what effect does this have When is cGMP PD active
Via a G protein - transducin Levels of cGMP are lowered Phosphodiesterase is active in light **CLOSURE of cGMP gated ion channels**
38
Flow of ions in the dark MP created
* Na+ inward current in OUTER segment * K+ outward current in inner segment * Creates MP of -40 mV
39
Movement of ions in the light
Na+ inward current is stopped K+ outward current is maintained Creates hyperpolarisation
40
Arrangement of neurons in retina
41
Axons of what structures form the optic nerve
Axons of ganglion cells
42
Where is there a blind spot in our eye
No rods and cones where the optic nerve leaves the eye
43
Where are cones found
Macula - specifically fovea
44
What NT do rods and cones release How does the release vary in dark and light
Glutamate NT released in dark Reduced glutamate release in light Hyperpolarisation moves potential away from threshold, reducing the likelihood of NT being released
45
What receptors are found on bipolar cells
Glutamate receptors IONOTROPIC - AMPA and kainate METABOTROPIC - mGluR6
46
What does lateral inhibition allow
Transmission of high integrity info towards the brain
47
Bipolar cells express \_\_\_\_ What effect does this have on the signal transmitted
EITHER ionotropic or metabotropic receptors Equal and opposite respons to light signal
48
Centre for metabotropic receptors on bipolar cells
On centre
49
Centre for ionotropic receptors on bipolar cells
Off centre | (Signal passed to ganglion cells)
50
Ionotropic glutamate receptors found on bipolar cells - MOA
**AMPA and Kainate** Glu binding leads to activation of ligand gated Na+ ion channel and subsequent depolarisation of the bipolar cell Off centre
51
Metabotropic glutamate receptors found on bipolar cells - MOA
**mGluR6** Glu binding leads to closure of cGMP gated Na+ channels and subsequent hyperpolarisation of bipolar cell On centre
52
Effect of lateral inhibition
Enhanced quality of sensory info through lateral inhibition
53
What do the on vs off centres allow for
Contrast info which enables visual acuity e.g. enables ability to detect stimuli against a background 1/2 of cells check for stimuli brighter than background Other 1/2 check for stimuli darker than background = and opposite responses in on & off centre cells
54
Pathway of light through cells of retina NT of bipolar cells what are the receptors on ganglion cells and what do they cause
Bipolar cells - Glu as NT Ionotropic receptors on ganglion cells - AMPA, kainate and NMDA Depolarisation produced in ganglion cells APs generated
55
Cells involved in lateral inhibition
Horizontal cells Amacrine cells +ve signal to 1 cell and -ve signal to another APs generated
56
P cells - parvocellular vision
Numerous Small receptive fields (smaller jigsaw pieces - a piece of this retina is sent to brain and put back together in the visual cortex - carried ganglion cell by ganglion cell) Colour sensitive High visual acuity High spatial resolution
57
M cells - magnocellular division
Large receptive fields (large jigsaw pieces) Fast conducting Motion perception, rapidly changing detail (highly myelinated) High temporal resolution
58
K cells
Transmit colour blue (used to be part of P cell group)
59
What does the arrangement of the visual pathway allow for
Depth perception
60
Subcortical targets of visual pathway
Pretectum Superior colliculus Suprachiasmatic nucleus of hypothalamus Lateral geniculate nucleus of thalamus (cerebral cortex - perception of vision)
61
Pretectum
Blinking response
62
Superior colliculus
Head and eye movements (can see movement out of side of eye)
63
Suprachiasmatic nucleus of hypothalamus
Circadian rhythms
64
Lateral geniculate nucleus of thalamus
90% of ganglion fibres
65
10% of ganglion fibres go to
Pretectum Superior colliculus Suprachiasmatic nucleus of hypothalamus
66
Visual pathway
67
Synonym for tunnel vision
Bilateral hemianopia
68
Visual pathway structures
69
Lateral geniculate nucleus proportion of retinal axons organisation 1/2 of representation is \_\_\_\_\_\_ How is it divided
90% of retinal axons Retinotopic organisation/map (jigsaw) 50% of representation = fovea 6 layers of cell bodies separated by intralaminar layers
70
Layer 1 & 2 (ventral)
Magnocellular layer Receive input from M cells Motion - big receptive field
71
Layers 3-6 (dorsal)
Parvocellular layer Receive input from P cells Fine detail
72
1, 4, 6
Contralateral nasal hemiretina
73
2, 3, 5
Ipsilateral temporal hemiretina
74
Breakdown of lateral geniculate nucleus
75
Sensory signal from LGN →
4Cβ
76
Magnocellular cells →
4Cα | (allows us to actually see)
77
Difference between layers 3, 4, 5
3 & 5 - thicker in motor output 4 - thick in sensory cortex
78
Organisation of cerebral cortex
79
BA of primary visual cortex
17 visual area 1 6 layers of cells
80
Where do inputs from LGN enter
In layer 4
81
sublayers of layer 4 (where input from LGN enters)
4A 4B 4α 4β
82
4Cβ Axons of P cells terminate on simple cells - detail info
83
4Cα
Axons of M cells terminate on simple cells Motion info
84
Layers 2 & 3
Axons from intralaminar region of LGN terminate in layers 2 & 3 where they innervate blobs - colour info
85
Arrangement of layers
86
Structure of blobs
87
Magnocellular pathway
V1 → V2 → V3 → MT Dorsal pathway Posterior parietal cortex V3 = orientation, position MT = object movement
88
Parvocellular pathway
V1 → V2 → V4 Ventral pathway Inferior temporal cortex V4 - colour, form, shape, texture
89
M
Dorsal/parietal pathway Motion Change
90
P
Ventral/temporal pathway Form Detail
91
Where is the fovea found
Follow dotted line to retina
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CNS (36 decks)

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