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BMS1052 > SENSORY SYSTEMS: VISION > Flashcards

SENSORY SYSTEMS: VISION Flashcards

1
Q

What is the fovea?

A

Area of the eye that has the highest density of photoreceptors - so highest visual aucity (quality)

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2
Q

Why are there no photoreceptors in the blind spot?

A

Because there are blood vessels coming out

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3
Q

What are objects coming in the eye further than 6m saif to be?

A

PARALLEL

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4
Q

What is normal image formation known as (normal eye) ?

A

Emmetropia

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5
Q

In a normal eye, what does the lens do when far light (>6m ) is entering eye?

A

LENS FLATTENS

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6
Q

What does the lens do if there is a close light source?

A

LENS IS ROUNDER (due to ciliary muscles relaxing) so it has a high refractive power (bending the light)

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7
Q

What is myopia?

A

When the eyeball is too long/lens too strong.

- Light is focused further inside orbit and doesn’t reach the back of the eye

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8
Q

How is myopia corrected?

A

With a CONCAVE LENS

- diverges light rays before they enter the eye

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9
Q

How is hyperopia corrected?

A

With a convex lens, converges light rays before they hit the eye

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10
Q

What is presbyopia?

A

Far sightedness due to loss of elasticity in the lens (common with aging)

  • inability to accomodate in the long term
  • reading glasses or multifocal as treatment
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11
Q

What is the info flow once light reaches the retina?

A

Photoreceptors–> bipolar cells–> ganglion cells

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12
Q

Which direction does light go?

A

The opposite way to info flow

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13
Q

What is the pathway of light and info processing?

A

Light ENTERS retina–> passes through all ganglion and bipolar cells then reaches the photoreceptors__> then once here the photoreceptors (rods and cones) transduce light and info flows BACK form photoreceptors–> bipolar cells–> ganglion cells–> until reaching the optic nerve

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14
Q

What is astigmatism?

A

Blurry image-rotational assymetries in area

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15
Q

What are rods?

A

HIGH LIGHT SENSITIVITY

  • So active in LOW LIGHT LEVELS
  • have more pigment
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16
Q

What is scotopic vision?

A

In the nighttime light where ONLY THE RODS ARE ACTIVE (not cones)

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17
Q

What are cones?

A

Photoreceptors active in HIGH LIGHT LEVELS - Only snesitive to DIRECT LIGHT ( because of their shape)

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18
Q

How many types of cones are there?

A

3 types

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19
Q

What is photopic vision?

A

Daylight where only CONES ARE ACTIVATED

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20
Q

What is mesopic vision?

A

twilight vision (Rods and cones active)

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21
Q

What are disks in rods and cones filled with?

A

Opsin which is a protein that absorbs light

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22
Q

In the darkness, what occurs when the rod mempot is -30mV?

A

It is HIGHLY DEPOLARISED due to Na+ channels being kept open by cGMP which is continually produced in the PHOTORECEPTOR (this is very metabolically expensive)

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23
Q

What occurs when light reaches the eye in terms of pathways in the ROD cells?

A

Light activates a cascade–> light sensitive protein (photopigment rhodopsin in rods) undergoes conformational change–> this activates a G protein –> this then activates phosphodiesterase enzyme (reduces the cGMP levels)—> Results in CLOSING OF NA+CHANNELS AND HYPOERPOLARISES CELL

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24
Q

What determines which colours rods or cones respond to?

A

Light waves absorbed by opsin/rhodopsin

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25
Q

What does the rate at which glutamate (neurotransmitter) is released depen upon?

A
  • mempot

- More POSITIVE mempot= HIGHER RATE of neurotransmitter release (means Na+ channels will be open)

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26
Q

What does light lead to?

A

Mempot becoming more negative (less glutamate release, less cGMP) so Na+ channels close

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27
Q

What are blue cones best activated by?

A 
Short wavelength (opsin proteins in blue cones will most easily absorb short wavelengths 
(BUT in general, RODS have a higher sensitivity -so more likely to absorb photons)
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28
Q

What is colour perception based on?

A

RELATIVE ACTIVATION OF the 3 cone classes

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29
Q

Are dogs colour blind?

A

no! Just less sensitive to colours as they have 2 instead of 3 cones

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30
Q

What wavelengths do green cones absorb?

A

Medium wavelength

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31
Q

What do red cones absorb?

A

Long wavelength

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32
Q

What determines the size of the ganglion cells receptive field?

A

Spacial extent of horizontal cells axons and the ganglion cells dendrites

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33
Q

What is spacial aucity?

A

The smallest feature you can recognise/how well you can resolve 1 form 2 pts of light

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34
Q

What does the snellen chart test?

A

The aucity in the fovea

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35
Q

What does 20/40 (6/12) vision mean?

A

You are short sighted

- can only read down to the line that poeple who are 12m away can read

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36
Q

What is the central retina dominated by?

A

Cones about 0.5 microm in diameter

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37
Q

What is the peripheral retina dominated by?

A

Rods

(4 microm) - much larger as only needed for gross detail; not finer detail

38
Q

What does spatial aucity depend on?

A
  • Receptor density and convergence ratio( desity of cones and convergence of cones to ganglion cells-outputs)
  • aucity is reduced if you have blurry vision
39
Q

Where do ganlgion cells exit eyeball?

A

Blindspot

40
Q

What is the receptive field?

A

Region of visual space in which light affects a cells mempot

41
Q

What are OFF bipolar cells?

A

They are HYPERPOLARISED by light in RF centre and DEPOLARISED by light in RF surround
- Characterised by ionotropic glutamate gateed cation channels (excitatory)

42
Q

What are ON bipolar cells?

A

They are DEPOLARISED by light in the RF centre and HYPERPOLARISED BY light in RF surround.

  • invert the sign of photoreceptors
  • Characterised by metabotropic G prtein coupled receptros
43
Q

What does a inverted photorecpetro signal mean (in ON bipolar cells)

A

Increased i lumination= less glutamate so the cell is more depolarised-graded

44
Q

What does having a surround strucucture in ON OFF bipolar cells help with?

A

Specifically locating where the stimulus is

45
Q

What do on/off centre bipolar cells target?

A

Target the corresponding ON OFF ganglion cells

46
Q

What happens when spinning your head to the left?

A

You get INCREASED snesory inputs from the LEFT HORIZONTAL CANAL.

  • Signal sent to medial vestibular nucleus
  • Here it can either be inhibitroy projection (ipsilateral side- inhibitory allows opposite motor commands from eyes) or a excitatory projection (contralateral side)
47
Q

What are the two main functional visual streams?

A

Parietal and Temporal

48
Q

What does the parietal visual stream involve?

A

The ‘where are things going’ - so action

49
Q

What does the temporal visual stream involve?

A

The “what” - so perception- Identification of objects

50
Q

What does the MT area process?

A

MT-motion

51
Q

What does the V 4 cortical area process?

A

Shape and colour (eg. some neurons could respond more to concave/convex curvature)

52
Q

What does the TE cortical area process?

A

TE- object recognition (faces and images of hands)

53
Q

How do V4 and MT act?

A

In PARALLEL with MT extracting motion information and V4 extracting shape and colour

54
Q

How do photoreceptors work?

A

In parallel

55
Q

What is serial processing?

A

Each information is processed one at a time. For example the ventral (temporal stream):
V1 extracts orientation info
V4 extracts simple shapes
TE contains neurons that encode objects and faces

56
Q

Is there divergence from retinal cells to ganglion cells?

A

Yes , ganglion cells have overlapping receptive fields

57
Q

What is the receptive field of one neuron?

A

Region of visual space in which flash of light will change mempot

58
Q

How many parallel circuits are there for ganglion cells?

A

More than 12 with unique classes of ganglion cells

- All have different function and if you organise them based on function, RFs do not overlap

59
Q

What are parasol cells and which pathway are they involved in?

A

Also known as M type cells (type of ganglion cell)
- Part of the parietal pathway
- Have LARGE CELL bodies, dendritic arbours, receptive fields
- Sensitive to rapidly chanfging stimuli
- NOT COLOUR SENSITIVE (only care how BRIGHT it is (luminance contrast- also receive more inputs from rod cells) lower contrasts, larger region of space that they collect from )
(Layers 1,2 of LGN)

60
Q

What are midget cells and what pathway are they involved in?

A

A type of ganglion cell (Parvocellular–> Layers 3-6 upper)

  • AKA midget cells
  • Part of the temporal (ventral) pathway-distinguishes colours
  • Have SMALL cell bodies dneritic arbours RFs
  • sensitive to FINE stimulus features (don’t integrate scross as many photoreceptors)
61
Q

Why are parasol cells also known as M cells?

A

Because they project into the Mgnocellular layers of the Lateral Geniculate Nucleus

62
Q

What types of inputs do parasol cells recieve?

A

Excitatory synapses from diffuse bipolar cells

63
Q

Where to Midget cells project to?

A

The Parvivocellar LGN layers (parvo=object recognition)

- Also known as P cells

64
Q

Where are midget cells primarily found?

A

In the fovea

65
Q

Where does information go from the retina?

A

Can go to the Pretectum (reflex control of pupil and lens)

OR can go to the Lateral Geniculate Nucleus

66
Q

What is the LGN for?

A

Gateway to cortex and CONSCIOUS vision

  • 90% of retinal projections are to LGN and then projections are sent to the cortex)
  • It is for PARALLEL processing
  • contains 6 layers (6 parallel representations of the contralateral visual field)
67
Q

What is the pretectum for?

A

Reflexive eye movements and pupil size

68
Q

What is the superior colliculous for?

A

Controls eye and head orientating responses

69
Q

What is the suprachiasmatic nucleus?

A

Circadian rhythms

70
Q

What is binocular vision?

A

Where you can see both visual fields (stereoscopic vision)

- you make judgements about depth

71
Q

What is decussation and what does it allow us to do?

A

Axons from NASAL retina cross overand axons from TEMPORL retian DO NOT CROSS OVER
-Allows both eyes to see a part of visual field from other eye (evolved to be like that)

72
Q

What does the left visual cortex represent?

A

The RIGHT visual field

73
Q

What does the right visual cortex represent?

A

The LEFT visual field

74
Q

What happens when you transect an optic nerve/

A

Visual field is the equivalent of closing one eye

75
Q

What happens when there is a transection of the optic tract, or the LGN or V1?

A
  • You only see things in one hemifield

- but both eyes are still functional

76
Q

What happens when the there is a transection of the optic chiasm?

A

Both eyes will still function but you lose stereoscopic vision (it will be monocular)

  • Only crossing fibres affected
  • central left visual field only being processed by the right eye
77
Q

What is a bitemporal hemianopia?

A

Half vision in each eye due to a pituitary tumor

78
Q

What are layers 1 &2 of the LGN for?

A

Magnocellular layers - (poor spacial aucity, low contrast, monochromatic, high temporal aucity )
- Inputs from parasol retinal ganglon cells (motion)

79
Q

What are layers 3-6 of LGN?

A
  • Parvocellualr layers
  • Inputs from midget retinal ganlion cells
  • Colour, fine spatial aucity
80
Q

Where do layers 1,4 and 6 recieve inputs from?

A

Contralateral eye

81
Q

Where do layers 2,3,5 receive inputs from?

A

Ipsilareral eye (temporal retina)

82
Q

What are some other names for the primary visual cortex?

A

V1, Brodmanns area 17, or striate cortex

83
Q

What K cells target?

A

Layers II and III

84
Q

What is a LGN ON cell similar to?

A

A retinal cell

85
Q

Simple and complex cells..

A

RESPOND BEST TO ELONGATED BARS/EDGES

86
Q

What are simple cells?

A
  • Have spatially segregated on/off subregions
  • Position of bar within RF is important
  • Are often monocular, respond to inputs coming from only one eye(projections from retina–>LGN–> cortex) only coming from one eye
  • moving positions of the bar slightly changes response
87
Q

What are complex cells?

A
  • Almost all are binocular
  • spatially HOMOGENOUS receptive fields ( no segregation of on/off subregions)
  • POSITION OF LIGHT BAR WITHIN RF NOT IMPORTANT
88
Q

What do adjacent neurons in V1 respond to ..

A

Stimuli on adjacent regions of the visual field

89
Q

What is the concetration of rods like as you move further from the fovea (eccentrictiy in degrees)?

A

Concentration of rods is progressively less!

90
Q

What do the superior colliculi do?

A

Play a role in generating orienting head and eye movements to sudden visual (and other sensory) stimuli
- superficial layers soley process visual information

BMS1052 (14 decks)

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