Physiology of Vision

Question 1

What are the lateral cells in the retina?

Answer 1

horizontal cells and amacrine cells

Question 2

What is the function of horizontal cells?

Answer 2

receive input from photoreceptors and project to other photoreceptors and bipolar cells

Question 3

What is the function of amacrine cells?

Answer 3

receive input from bipolar cells and project to ganglion cells, biopolar cells and otehr amacrine cels

Question 4

What is transduction?

Answer 4

the conversion of electromagnetic radiation to neural signals

Question 5

What are the 4 regiosn of photoreceptrs?

Answer 5

outer segment; inner segment; cell body and synpatic terminal

Question 6

What is the resting membrane potenetial of photoreceptors as compared to other neurons?

Answer 6

depolarised

Question 7

What happens to the membrane potenetial of photoreceptors in response to light?

Answer 7

hyperpolarises

Question 8

What is the dark current?

Answer 8

constant flow of sodium through a cGMP channel that is open in the dark and closed in the light

Question 9

What is the visual pigment in rods called?

Answer 9

rhodopsin

Question 10

What is rhodopsin composed of?

Answer 10

retinal and opsin

Question 11

What happens to retinal in the light?

Answer 11

changes from 11-cis-retinal to all-trans-retinal

Question 12

How does the activation of retinal cause closure of cGMP channels?

Answer 12

activats transducin and a molecular casacade that decreases cGMP

Question 13

What is the neurotransmitter in the retinal ganglion cells?

Answer 13

glutamate

Question 14

What is visual acuity largely determined by?

Answer 14

photoreceptor spacing

Question 15

What are the differences between the distribution of rods and cones?

Answer 15

more convergence in rod system which increases sensitivity whilst decreasing acuity

Question 16

What are the 3 types of cone?

Answer 16

short-wave; middle-wave and long-wave cones

Question 17

What type of glutamate receptor is foudn in OFF bipolar cells?

Answer 17

ionotropic

Question 18

What type of glutatmate receptor is foudn in ON bipolar cells?

Answer 18

metabotropic

Question 19

What is the difference between ON and OFF bipolar cells?

Answer 19

ON bipolar cells are activated light ON (less glutamate) whereas OFF bipolar cells are activated by light OFF

Question 20

What is the function of lateral inhibition?

Answer 20

exaggerates the difference in stimulus intensity detected by adjacent neurons, aiding localisation

Question 21

What is the function of centre-surround organisation?

Answer 21

emphasis contrast sharpening boundary between objects of different luminance

Question 22

What ar ethe 2 types of retinal ganglion cell?

Answer 22

M-type ganglion cell and P-type

Question 23

What is the difference between M-type and P-type ganglion cells?

Answer 23

M-type have much larger receptive fields, they conduct APs more rapdly and are more sensitive to low contrast stimuli. thye respond to stimulation of their RF centre with a burst of APs whereas P-type respond with a sustained discharge

Question 24

What are the 2 typeso of colour opponency?

Answer 24

red vs green and blue vs yellow

Question 25

What type of retinal ganglion cells are color-opponent cells?

Answer 25

P-type and nonM-nonP

Question 26

How many layers does the lateral geniculate nucleus have?

Answer 26

6

Question 27

What are the ventral layers of the LGN (1 and 2) called?

Answer 27

magnocellular LGN layers

Question 28

What are the dorsal layers (3-6) of the LGN called?

Answer 28

parvocellular LGN layers

Question 29

Where do nonM-nonP type retinal ganglion cells project in LGN?

Answer 29

konio-cellular layers-- numerous tiny neurons just ventral to each layer

Question 30

Where do magnocellular LGN neurons project to in the visual cortex?

Answer 30

layer IVCa

Question 31

Where do parvocellular LGN neurons project to in the visual cortex?

Answer 31

layer IVCb

Question 32

Where do koniocellulal LGN axons project to?

Answer 32

layers II and III

Question 33

Where are the first binocular neurons found in the visual cortex?

Answer 33

in layer III

Question 34

What is the competition hypothesis?

Answer 34

connections from the two eyes compete with each other in cortex

Question 35

What is the function of direction selectivity of the striate cortex?

Answer 35

analysis of object motion