Photoreceptors

Question 1

what are the 2 photoreceptors?

Answer 1

-rods
-cones

Question 2

what is the pacinian corpuscle and describe the structure

Answer 2

a receptor that responds to pressure changes

it’s located deep in the skin, and it consists of 1 sensory neurone wrapped in tissue, separated by gel. this has stretch-mediated sodium channels in the plasma membrane.

Question 3

what is the role of the sodium channels in the pacinian corpuscle and what happens during the resting state?

Answer 3

the stretch-mediated sodium channels open to allow sodium ions to enter the sensory neurone, but ONLY when deformed, establishing an action potential. only when pressure is applied does this happen.

in the resting state, they are too narrow for this diffusion.

Question 4

what is visual acuity?

Answer 4

the ability to distinguish between points that are close together

Question 5

where are rods located?

Answer 5

the peripheral part of the retina

Question 6

where are cones located?

Answer 6

the fovea

Question 7

what colour do rods see images in and why?

Answer 7

black and white because they can’t distinguish between different wavelengths of light

Question 8

what colour do cones see images in and what does this depend on?

Answer 8

colour but it depends on which cone cells are stimulated.

Question 9

what are the 3 types of cone cell?

Answer 9

red sensitive
blue sensitive
green sensitive

Question 10

how sensitive are rod cells to light and how does this work?

Answer 10

very sensitive, so they work in dim light

little energy is needed to break down the rhodopsin and they have retinal convergence-many rods join 1 bipolar neurone, so many weak action potentials combine to trigger one.

Question 11

what is the pigment broken down in rods?

Answer 11

rhodopsin

Question 12

what is retinal convergence?

Answer 12

when many rods join 1 bipolar neurone, so many weak action potentials combine to trigger one.

Question 13

do rods have high or low visual acuity and why?

Answer 13

low due to being close together

Question 14

what is the pigment broken down in cones?

Answer 14

iodopsin

Question 15

how sensitive are cone cells to light and how does this work?

Answer 15

less sensitive, so they work in bright light

more light is needed to break down the iodopsin and trigger an action potential, and 1 cone joins 1 bipolar neurone . therefore there is no spatial summation, so no retinal convergence

Question 16

do cones have a high or low visual acuity and why?

Answer 16

high due to being further apart

Question 17

describe the distribution of rods and cones

Answer 17

it is uneven, because light is focused by the lens on the fovea which receives the highest light intensity. therefore, there are lots of cone cells here. rod cells are further away in the peripheral parts, due to the lower light intensity there. in the blind spot, there is neither.