Photoreceptors

Question 1

where are the photoreceptors located?

Answer 1

in the retina

Question 2

what is the conversion of light to electrical signals called?

Answer 2

phototransduction

Question 3

What are the two main photoreceptors in the retina?

Answer 3

cones and rods

Question 4

does our eye contain more cones or rods

Answer 4

rods

Question 5

T/F. photoreceptors release action potentials?

Answer 5

false they respond to stimuli with graded membrane potentials

Question 6

basic structure of cones and rods

Answer 6

their membrane folds into disk like layers which contain visual pigments

the inner segment contains the nucleus and organelles for protein synthesis

in the basal layer the synapse release glutamate

Question 7

which direction do both cones and rods point to

Answer 7

the back of the eye

Question 8

how do photoreceptors detect light

Answer 8

they use membrane bound visual pigments.

when light hits these pigments they change shape, causing a chemical cascade that hyperpolarizes the cell reducing glutamate release

Question 9

why are photoreceptors more active in the dark?

Answer 9

because there is less light hitting the pigments, depolarizing the cells triggering more release of glutamate

Question 10

why is glutamate release important in the eye?

Answer 10

because it helps transfer visual information

Question 11

what is the pigment found in rods?

Answer 11

rhodopsin

Question 12

how many pigments are in cones

Answer 12

3

Question 13

how are photoreceptors distributed in the eye

Answer 13

not uniformly, instead they are packed in the macula a central disk and also packed tightly in the fovea

Question 14

fovea

Answer 14

the fovea is used for detailed vision

Question 15

are there photoreceptors in the blind spot?

Answer 15

no, this is where axons carrying visual information exit the eyeball to form the optic nerve

Question 16

What type of light are cones used for?

Answer 16

bright light because they are less sensitive than rods

they distinguish colours but don’t operate in dim conditions

Question 17

what type of light are rods used for?

Answer 17

dim light, in sunlight they are bleached out, meaning that their rhodopsin is broken down

Question 18

does the fovea contain an even amount of cones and rods?

Answer 18

no fovea contains almost only cones

Question 19

Where is the rod presence concentrated?

Answer 19

in the peripheral retina

Question 20

what are the three layers of neurons in the retina

Answer 20

photoreceptors synapse on the bipolar cells and those synapse on the ganglion cells

Question 21

where is convergence strongest in the eye? Where is it weakest?

Answer 21

strongest in the peripheral retina and weakest in the fovea

Question 22

receptive field

Answer 22

every neuron in the visual system has a receptive/visual field. which is the region of the retina where the light affects the cell’s activity- the set of photoreceptors which affect the cell

Question 23

what type of receptive field do bipolar cells have?

Answer 23

center-rounded fields with round center region and doughnut shaped surround

Question 24

what does it mean that bipolar cell receptive field can be on/off center

Answer 24

on center means the cells are excited by light in the center of field and inhibited by light in the surround.

off center means cells are inhibited by light in the center and excited by light in the surround

Question 25

what do on center cells respond the most to? off-center

Answer 25

on-center cells respond most when light fills their center and the surround is dark. off center respond best when a dark spot fills their center and the surround light

Question 26

what do bipolar cells react the strongest to?

Answer 26

when there is a contrast in light

Question 27

Do bipolar cells fire action potentials?

Answer 27

no, they respond with graded membrane potentials

Question 28

what is the major difference between ganglion cells and bipolar cells and photoreceptors

Answer 28

ganglion cells can fire action potentials

Question 29

how are ganglion and bipolar cells similar

Answer 29

ganglion cells can also be off/on centred meaning it responds well to contrast

Question 30

what does this emphasis on contrast explain

Answer 30

the chevreul illusion where left right hand bands seem darker than the middle even though it is the same color throughout

Question 31

where are ganglion cells most sensitive

Answer 31

in the periphery but poor at reporting spatial detail

Question 32

where are ganglion cells less senstive

Answer 32

near the fovea but they have better spatial resolution

Question 33

Magnocellular ganglion cells

Answer 33

provide information that is used by brain to infer movement- 10% of ganglion cells are M cells

Question 34

Parvocellular ganglion cells

Answer 34

provide information that is used to infer form and fine detail like texture. 70% of ganglion cells are P cells

Question 35

melanopsin ganglion cells

Answer 35

these are photoreceptors that have their own visual pigment- melanopsin- they project to suprachiasmatic nucleus a center for circadian rhythms

Question 36

how does visual information move>

Answer 36

ganglion cells> retina> brain

Question 37

optic chiasm

Answer 37

the point where the visual information crosses to the other side. Information from the nasal half of each retina cross the optic chiasm

Question 38

T/F. both nasal and temporal fibers cross the chiasm.

Answer 38

false only nasal fibers cross

Question 39

Why do fibers cross

Answer 39

because the right side projects to the left side and vise versa

Question 40

where does information move after crossing the chiasm?

Answer 40

goes from chiasm > thalamus> cortex

Question 41

what are the nerve bundles emerging from the chiasm called? Where do they end

Answer 41

the optic tracts. they end in the 2 lateral geniculate nuclei (LGN) in the thalamus

Question 42

where does LGN project

Answer 42

to the primary visual cortex (V1) via optic radiations

Question 43

where is the V1 located

Answer 43

in the occipital lobe

Question 44

how are visual areas in the brain organized? what does that mean?

Answer 44

retinotopically, meaning that neurons close to each other get information from close together parts of retina

Question 45

why does the fovea get a lot of space?

Answer 45

because it has many photoreceptors, bipolars, and ganglion cells, carrying lot of information

Question 46

fill in the blank. a large proportion of visual cells in the brain receive and process data from ______ photoreceptors.

Answer 46

foveal