Retina-11 and 12

Question 1

What is luminance expressed in?

Answer 1

logarithmic units of candella per square meter

Question 2

What kind of vision is the overlap between scotopic and photopic?

Answer 2

Mesopic

Question 3

Which type of vision has good acuity?

Answer 3

Photopic

Question 4

As luminance increases, what happens to the pupil area?

Answer 4

Decreases

Question 5

What range do our eyes cover in log cd/m2?

Answer 5

-6 to 10

Question 6

What range do rods cover?

Answer 6

-6 to 1

Question 7

What range to cones cover?

Answer 7

-3 to 10

Question 8

Where is the overlap in mesopic vision?

Answer 8

-3 to 1

Question 9

How many logarithmic units do rods cover?

Answer 9

7

Question 10

How many logarithmic units do cones cover?

Answer 10

13

Question 11

What is surface reflectance?

Answer 11

The percentage of light hitting an object that will be reflected

Question 12

If a light surface has a surface reflectance of 10%, and a light source with an intensity of 1000 hits that surface, what is the surface luminance?

Answer 12

100 (10% of 1000)

Question 13

What is the important factor when considering seeing things with different luminance, but the rations change the same with different source intensities?

Answer 13

The contrast (the object luminance/average luminance)

Question 14

On the sigmoidal curve, what happens with high gain adaptation?

Answer 14

The receptor response increases with only small increases in light level

Question 15

Why is there higher response at lower light levels?

Answer 15

Because light causes hyperpoalrisation

Question 16

Over how many logarithmic levels can cones adapt?

Answer 16

4

Question 17

How do cones cope with changing from dark to light light?

Answer 17

They can operate over 9 logarithmic units so that the large change in light intensity is at a high gain part of the curve so we can see the contrast.

Question 18

Retinal ganglion cells respond more to contrast than they do overall light intensity. true or false?

Answer 18

True

Question 19

What triggers the adaptation mechanism?

Answer 19

Low intracellular calcium ions due to closer of the cGMP-gates channels

Question 20

In the dark, what does high intracellular calcium do?

Answer 20

Inhibits synthesis of cGMP

Question 21

What happens in light?

Answer 21

Channel closes, so intracellular calcium ions decreases, reduced inhibition of guanylyl cyclase so more production of cGMP. Also increased affinity of the channels to bind cGMP via the action of calmodulin

Question 22

What protein increases the affinity of the channels to bind cGMP?

Answer 22

Calmodulin

Question 23

How do photoreceptors and horizontal cells play a role in light adaptation?

Answer 23

In the dark, photoreceptors are depolarised so release glutamate which activates horizontal cells to send an inhibitory feedback to the photoreceptors so they reduce glutamate. In light, photoreceptors hyperpolarise, so less glutamate release, less excitation of horizontal cells so less inhibition back to the photoreceptors so they hyperpolarise more strongly.

Question 24

Which cells generate slow graded potentials?

Answer 24

Bipolar, horizontal and amacrine cells

Question 25

How many cones do we have and where are they concentrated?

Answer 25

6 million- around the fovea

Question 26

What is the ratio of cone to gangion cells?

Answer 26

1-1

Question 27

Why do cones have greater spatial acuity?

Answer 27

Because each cone on the fovea connects to 1 ganglion cell, so signal generated by ganglion cell represents every single cone and spatial position on the fovea

Question 28

How many rods do we have?

Answer 28

120 million- densely packed in periphery

Question 29

Which photoreceptors show 1-1 convergenc?

Answer 29

Cones

Question 30

What is the receptive field?

Answer 30

The area of the retina dedicated to a part of the visual scene which is encoded by one ganglion cell

Question 31

Which cells carry the signal from the centre of the centre surround receptive field?

Answer 31

Bipolar cells

Question 32

Which cells provide lateral inhibition from the surround of the receptive field?

Answer 32

Horizontal cells

Question 33

What transmitter do horizontal cells release for lateral inhibition?

Answer 33

GABA

Question 34

Which cells mediate sustained-transient temporal properties?

Answer 34

Amacrine cells

Question 35

An ON-bipolar cell expresses what glutamate receptor?

Answer 35

MGluR6

Question 36

Which bipolar cell inverts the signal when light hits the centre of an ON-centre receptive field?

Answer 36

ON-bipolar cell

Question 37

Describe the process of light hitting the centre of an ON-centre receptive field

Answer 37

The cone cell in the centre hyperpolarises and releases less glutamate. The ON-bipolar cell with MgluR6 inverts this signal so releases more glutamate which is received by AMPA on the ON-ganglion cell which causes excitation. When less glutamate is received by AMPA on the OFF bipolar, it releases less glutamate onto the OFF ganglion AMPA, so this fires less.

Question 38

What do horizontal cells release onto photoreceptor terminals?

Answer 38

GABA

Question 39

What are the two types of synapse?

Answer 39

Conventional and ribbon

Question 40

Describe a conventional synapse

Answer 40

transient vesicle release in response to depolarisation and calcium. postsynaptic response is fast and brief, slow replenishment

Question 41

Describe a ribbon synapse

Answer 41

for longer, sustained, high-frequency transmission found in sensory systems. Synaptic ribbon holds vesicles close to the membrane. exocytosis is graded, so more depolarisation means more vesicle release. vesicles are replenished quickly

Question 42

Where are ribbon synapses found in the retina?

Answer 42

In photoreceptor and bipolar cell terminals where transmission is continuous

Question 43

What is the action of an A2 amacrine cell?

Answer 43

If a rod bipolar cell is excited, it will release glutamate onto an A2 amacrine cell which will depolarise it. depolarisation moves through gap junctions to depolarise an ON-cone bipolar cell which results in activation of ON cone ganglion cell. A2 amacrine cell also makes inhibitory connection with the OFF-cone bipolar cell so OFF pathway is never triggered by the rod pathway

Question 44

What are W3 ganglion cells?

Answer 44

They respond most to small moving objects on a featureless background

Question 45

What are the 3 classes of ganglion cells?

Answer 45

Midget/Parasol/Projecting Parvocellular/Magnocellular/Koniocellular P/M/K

Question 46

Which type of ganglion cell is for the what pathway?

Answer 46

P cells- parvocellular

Question 47

Which type of ganglion cell is for the where pathway

Answer 47

M cells- magnocellular

Question 48

Where does the distinction between the what and where pathway become distinct?

Answer 48

The lateral geniculate nucleus

Question 49

What is a feature of P cells?

Answer 49

They have chromatic antagonism called opponent chromatic organisation

Question 50

What is optic neuropathy?

Answer 50

Degeneration of ganglion cells and optic nerve

Question 51

What are some optic neuropathies?

Answer 51

Glaucoma, mitochondrial disorders, multiple sclerosis, diabetic rhetinopathy

Question 52

What are photoreceptor dystrophies?

Answer 52

Degeneration of photoreceptors so light is not converted into electrical signal

Question 53

What are some examples of photoreceptor dystrophies?

Answer 53

Age related macular degeneration, retinitis pigmentosa

Question 54

Why are photoreceptor dystrophies easier to treat than optic neuropathies?

Answer 54

Easier to stimulate ganglion cells at retinal level than to try and stimulate visual centres in the brain

Question 55

What is retinal prosthetics?

Answer 55

Stimulating an area of retinal ganglion cells by using an electrode array to bypass the photoreceptors

Question 56

What is optogenetic prostheses?

Answer 56

Stimulating channel rhodopsin expressing cells with light- a form of gene therapy