5.8

Question 1

Retina contains light-sensitive cells:

Answer 1

rods and cones

Question 2

Rods and cones are

Answer 2

receptor cells

Question 3

a receptor cell is able to

Answer 3

detect changes in the environment and converts sensory information into a form that can be transmitted to the CNS

Question 4

The light has to travel through several layers of neurones to reach the

Answer 4

light-sensitive rods and cones

Question 5

Underneath the rods and cones is a layer of cells containing the pigment, melanin which

Answer 5

absorbs any light that is not absorbed by the rods and cones

Question 6

(Rods) outer segment contains many vesicles of the light-sensitive pigment

Answer 6

rhodopsin

Question 7

when light hits a rod cell it causes the rhodopsin to

Answer 7

split into opsin and retinal

Question 8

(rods) when rhodopsin splits it is a process known as

Answer 8

bleaching

Question 9

Bleaching results in the permeability of the rod cell to sodium ions to be

Answer 9

altered

Question 10

Rod cells set up a

Answer 10

generator potential

Question 11

(ROD GP) if this is enough to overcome the threshold value, an AP is generated in the sensory neurone which carries the impulse along the

Answer 11

optic nerve to the brain

Question 12

after, the rhodopsin is regenerated, which requires energy from

Answer 12

ATP

Question 13

Rod cells are extremely sensitive to low light intensities, so they are most useful for

Answer 13

vision in dim light

Question 14

rod cells cannot distinguish between different wavelengths, so they produce black and white images only, known as

Answer 14

monochromatic vision

Question 15

several rods synapse with just one sensory neurone - means that rod cells have

Answer 15

low visual acuity

Question 16

Grouping of rod cells together also increases their sensitivity known as

Answer 16

summation

Question 17

if each of the several rod cells results in a tiny amount of neurotransmitter being released into the synaptic cleft, these small amounts ‘add together’ so that there is enough to set up an

Answer 17

action potential in the sensory neurone

Question 18

there are many more rod cells in the retina than

Answer 18

cones

Question 19

rods are found evenly spread across the retina, although there are very few at the

Answer 19

fovea

Question 20

cones are similar in structure to rods, but contain a pigment of

Answer 20

iodopsin

Question 21

(Cones) 3 different kinds of iodopsin each sensitive to

Answer 21

red, green or blue light

Question 22

(cones) different colours are perceived depending on the

Answer 22

proportion of the different types of cone that are stimulated

Question 23

(CONES) e.g. if red and green cones are stimulated equally, the brain interprets the colour as yellow. this is called the

Answer 23

trichromatic theory of colour vision

Question 24

cone cells are not as sensitive to light as rods, so they only work in

Answer 24

high light intensity

Question 25

there are fewer cones than rods in the

Answer 25

retina

Question 26

most of these cone cells are concentrated at the

Answer 26

fovea

Question 27

the fovea is the part of the retina where the centre of the image is focused when you

Answer 27

look straight at an object

Question 28

most cones have an individual connection to a sensory neurone, meaning that

Answer 28

cones have much greater visual acuity than rods