L33 - visual defects

Question 1

vitreous humour

Answer 1

viscous jellylike substance that lies between the lens and the retina

Question 2

conversion of light into neural activity

Answer 2

• 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

Question 3

pigment epithelium

Answer 3

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

Question 4

what do bipolar neurones release

Answer 4

glutamate

Question 5

phototransduction

Answer 5

conversion of light energy into electrical energy

Question 6

where in cones does phototransduction occur

Answer 6

invaginated membrane

Question 7

where in rods does phototransduction occur

Answer 7

membranous discs

Question 8

photoreceptors in the dark

Answer 8

depolarised

continuously release glutamate

Question 9

photoreceptors in the light

Answer 9

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

Question 10

photopigments

Answer 10

individual transmembrane proteins

G-protein coupled receptors

Question 11

retinal

Answer 11

• embedded within photopigments

- synthesised from vitamin A

Question 12

what happens when retinal is hit with a photon if light

Answer 12

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

Question 13

resolution when denser photoreceptors

Answer 13

better

Question 14

on bipolar cells in light

Answer 14

depolarise

Question 15

off bipolar cells in light

Answer 15

hyperpolarise

Question 16

mechanism of off bipolar cells

Answer 16

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

Question 17

mechanism of on bipolar cells

Answer 17

• 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

Question 18

off bipolar cells as light gets dimmer

Answer 18

depolarises

Question 19

on bipolar cells as light gets dimmer

Answer 19

hyperpolarises

Question 20

receptive field

Answer 20

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

Question 21

outer retina receptive field

Answer 21

horizontal cells shape receptive fields of bipolar cells

Question 22

inner retina receptive field

Answer 22

amacrine cells shape receptive fields of ganglion cells

Question 23

lateral inhibition

Answer 23

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

Question 24

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

Answer 24

cGMP molecules

Question 25

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

Answer 25

blue green red

Question 26

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

Answer 26

Photoreceptors further from the fovea are larger in size

Question 27

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

Answer 27

Rhodopsin

Question 28

What are the 2 colour opponent pathways?

Answer 28

red/green | blue ON/yellow OFF

Question 29

opsin

Answer 29

receptor protein of rhodopsin

Question 30

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

Answer 30

white

Question 31

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

Answer 31

maximum firing

Question 32

firing if green surrounds and red is in the centre

Answer 32

green inhibits the excitation of red in the centre

Question 33

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

Answer 33

pupillary light reflex | they connect the Edinger-Westphal nuclei

Question 34

striate cortex

Answer 34

primary visual cortex

Question 35

melanospin

Answer 35

5th photopigment | expressed by retinal ganglion cells

Question 36

where is melanopsin expressed

Answer 36

intrinsically photosensitive retinal ganglion cells

Question 37

groups of layers of the LGN

Answer 37

parvocellular magnocellular koniocellular

Question 38

layers 3-6 of the LGN

Answer 38

parvocellular (small cell bodies)

Question 39

layers 1-2 of LGN

Answer 39

magnocellular layers (large cell bodies)

Question 40

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

Answer 40

Koniocellular layers

Question 41

What do magnocellular cells receive input from?

Answer 41

M-type ganglion cells

Question 42

Magnocellular cells

Answer 42

- large receptive field - important for detection of stimulus movement - 5% population

Question 43

parvocellular cells

Answer 43

- smaller cell type | - 90% populations

Question 44

What do koniocellular cells receive input from?

Answer 44

K-type

Question 45

What do parvocellular cells receive input from?

Answer 45

P-type

Question 46

koniocellular cells

Answer 46

- medium cell type | - 5% population

Question 47

ganglion cells

Answer 47

M ganglion cells P ganglion cell K ganglion cell

Question 48

M ganglion cell

Answer 48

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

Question 49

P ganglion cell

Answer 49

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

Question 50

K ganglion cells

Answer 50

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

Question 51

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

Answer 51

They display the same orientation specificity

Question 52

what can be said about neighbouring columns

Answer 52

similar orientation but slightly shifted in angle

Question 53

What is an orientation column?

Answer 53

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

Question 54

Neurones in oblique rows display what kind of orientation specificity?

Answer 54

heterogenous

Question 55

what are blobs

Answer 55

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

Question 56

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

Answer 56

parietal lobe

Question 57

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

Answer 57

temporal

Question 58

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

Answer 58

Superior colliculus

Question 59

cytochrome oxidase

Answer 59

mitochondrial enzyme - cell metabolism