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control > L33 - visual defects > Flashcards

L33 - visual defects Flashcards

1
Q

vitreous humour

A

viscous jellylike substance that lies between the lens and the retina

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2
Q

conversion of light into neural activity

A
  • light is focused by the conea, then the lens, then passes through the vitreous humour to the retina
  • retina lies in front of the pigment epithelium which absorbs any light not absorbed by the retina
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3
Q

pigment epithelium

A

filled with black pigment melanin which absorb any light not absorbed by the retina
- stops light bouncing inside the eye, improving resolution

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4
Q

what do bipolar neurones release

A

glutamate

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5
Q

phototransduction

A

conversion of light energy into electrical energy

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6
Q

where in cones does phototransduction occur

A

invaginated membrane

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7
Q

where in rods does phototransduction occur

A

membranous discs

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8
Q

photoreceptors in the dark

A

depolarised

continuously release glutamate

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9
Q

photoreceptors in the light

A
  • depolarised ion channels close
  • photons are absorbed
  • membrane is hyperpolarised
  • glutamate release reduced
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10
Q

photopigments

A

individual transmembrane proteins

G-protein coupled receptors

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11
Q

retinal

A
  • embedded within photopigments

- synthesised from vitamin A

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12
Q

what happens when retinal is hit with a photon if light

A

it undergoes a conformational change, activating Rhodopsin molecule

  • G-protein coupled amplification
  • activates transuding and phosphodiesterase
  • breakdown of cyclic GMP
  • when levels fall, ion channels are closed
  • hyperpolarisation
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13
Q

resolution when denser photoreceptors

A

better

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14
Q

on bipolar cells in light

A

depolarise

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15
Q

off bipolar cells in light

A

hyperpolarise

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16
Q

mechanism of off bipolar cells

A
  • glutamate receptors
  • Na can permeate through and depolarise the cell
  • when light comes along, glutamate decreases and unbinds
  • ion channels close
  • hyperpolarisation occurs
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17
Q

mechanism of on bipolar cells

A
  • glutamate activates G-protein coupled receptor, inhibiting an ion channel
  • when light comes along, glutamate decreases, preventing inhibiting of the ion channel
  • depolarisation
  • releasing inhibition
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18
Q

off bipolar cells as light gets dimmer

A

depolarises

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19
Q

on bipolar cells as light gets dimmer

A

hyperpolarises

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20
Q

receptive field

A

the area of the retina that causes any change in response of a neurone

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21
Q

outer retina receptive field

A

horizontal cells shape receptive fields of bipolar cells

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22
Q

inner retina receptive field

A

amacrine cells shape receptive fields of ganglion cells

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23
Q

lateral inhibition

A

regions of retina which are outside the lateral extent of the dendrites of the ganglion cells
- form inhibitory synapses with ganglion cells

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24
Q

In dim light, the presence of which molecules causes ion channels in rod cells to open?

A

cGMP molecules

25
Q

The 3 types of cone cells can detect which 3 colours (each cone has 1 of 3 opsins)?

A

blue
green
red

26
Q

What happens to the size of photoreceptors further away from the fovea?

A

Photoreceptors further from the fovea are larger in size

27
Q

What is the name of the pigment in all rod cells called?

A

Rhodopsin

28
Q

What are the 2 colour opponent pathways?

A

red/green

blue ON/yellow OFF

29
Q

opsin

A

receptor protein of rhodopsin

30
Q

what colour do we see when all cone cells are equally active

A

white

31
Q

what type of firing if just red hits the centre of the receptive field

A

maximum firing

32
Q

firing if green surrounds and red is in the centre

A

green inhibits the excitation of red in the centre

33
Q

What are ipRGCs (intrinsically photosensitive retinal ganglion cells) required for?

A

pupillary light reflex

they connect the Edinger-Westphal nuclei

34
Q

striate cortex

A

primary visual cortex

35
Q

melanospin

A

5th photopigment

expressed by retinal ganglion cells

36
Q

where is melanopsin expressed

A

intrinsically photosensitive retinal ganglion cells

37
Q

groups of layers of the LGN

A

parvocellular
magnocellular
koniocellular

38
Q

layers 3-6 of the LGN

A

parvocellular (small cell bodies)

39
Q

layers 1-2 of LGN

A

magnocellular layers (large cell bodies)

40
Q

What is the name of the small layers between layers 1-6 in the LGN?

A

Koniocellular layers

41
Q

What do magnocellular cells receive input from?

A

M-type ganglion cells

42
Q

Magnocellular cells

A
  • large receptive field
  • important for detection of stimulus movement
  • 5% population
43
Q

parvocellular cells

A
  • smaller cell type

- 90% populations

44
Q

What do koniocellular cells receive input from?

A

K-type

45
Q

What do parvocellular cells receive input from?

A

P-type

46
Q

koniocellular cells

A
  • medium cell type

- 5% population

47
Q

ganglion cells

A

M ganglion cells
P ganglion cell
K ganglion cell

48
Q

M ganglion cell

A

Large fields allow them to be responsive to motion as they can compare the visual fields the whole time

49
Q

P ganglion cell

A
  • Provides more high resolution information
  • Only receiving input from bipolar cells connected to photoreceptors
  • Concerned with working out what the stimulus is
50
Q

K ganglion cells

A

works out which direction someone is coming towards you / object motion sensitive

51
Q

What can be said about all neurons in the vertical column?

A

They display the same orientation specificity

52
Q

what can be said about neighbouring columns

A

similar orientation but slightly shifted in angle

53
Q

What is an orientation column?

A

A column of the cortex of neurones that are all connected to each other and are selective to the same orientation of a stimulus

54
Q

Neurones in oblique rows display what kind of orientation specificity?

A

heterogenous

55
Q

what are blobs

A
  • pillars of neurones in the primary visual cortex
  • rich with cytochrome oxidase
  • where colour-processing occurs
56
Q

Information from the primary visual cortex is transmitted to which lobe for processing of visual motion?

A

parietal lobe

57
Q

Information from the primary visual cortex is transmitted to which lobe for recognition of objects?

A

temporal

58
Q

What is the part of the brain that is involved in working out where objects are relative to ourselves?

A

Superior colliculus

59
Q

cytochrome oxidase

A

mitochondrial enzyme - cell metabolism

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