The eye

Question 1

3 Aspects of vision controlled by photoreceptors?

Answer 1

Sensitivity to light
Sensitivity to colour
Visual acuity

Question 2

Photoreceptors

Answer 2

What can detect LIGHT waves as a stimuli

Question 3

What are the 2 photoreceptors in the eye?

Answer 3

Rods and cones

Question 4

Where are rods and cones detected?

Answer 4

The retina (back of) the eye

Question 5

What determines how we see in terms of photoreceptors?

Answer 5

The photoreceptors are stimulated by light waves so we can see the environment
These photoreceptors can determine differences in colour, detail (visual acuity) and brightness based on pigments/connection to optic nerves

Question 6

What photoreceptors has high light sensitivity?

Answer 6

Rods

Question 7

Rods having high light sensitivity means…

Answer 7

At LOW LIGHT levels they can be stimulated
As they are very light sensitive so not much light is needed to stimulate

Question 8

What photoreceptors have low light sensitivity?

Answer 8

Cones

Question 9

Cones having low light sensitivity means…

Answer 9

A lot of light is needed to stimulate them because they are not very sensitive to light

Question 10

What 2 factors explains the difference in light sensitivity between rods and cones?

Answer 10

The different pigments in rods and cones
The different connections rods and cones make to neurones

Question 11

Optical pigments

Answer 11

Rods and cones contain different pigments that can absorb light

Question 12

What optical pigment do rods have?

Answer 12

Rhodopsin

Question 13

What happens when optical pigments absorb light?

Answer 13

The light bleaches (breaks down) pigment which activates thus stimulates the photoreceptor (rod/cone) to send impulses to the brain

Question 14

What happens once optical pigment is bleached?

Answer 14

Sends impulses down optical nerve to the brain for a short time
Is then reformed to its initial state

Question 15

Why are rods not useful for bright light conditions?

Answer 15

Because they are very photosensitive so in bright light, all rhodopsin in rods are rapidly bleached
To become responsive to light again, rhodopsin must be reformed but it take a while to be reformed so not useful for bright lights

Question 16

Why is iodopsin useful in bright light?

Answer 16

Because when it’s bleached due to bright light, it can be reformed quickly again to receive more light thus see again

Question 17

What optical pigments do cones have?

Answer 17

Iodopsin

Question 18

Sequence of how absorbance of light sends impulses to the brain?

Answer 18

Light absorbed by photoreceptor
Neurotransmitter released across synapse to nearby neurone
Neurone is only activated if enough stimulation by neurotransmitter thus enough light absorbed
So there is a threshold neurotransmitter that must be released to actually send impulse to brain

Question 19

Why are rods better at seeing in low light levels due to their connections to neurones?

Answer 19

SEVERAL rods are connected to a single neurone which have high light intensity so can detect light even in the dark
So even when stimulation of rods is low due to low light intensity, it is more likely enough neurotransmitter will be released to reach neurone’s threshold and send an impulse to the brain

Question 20

Why do cones have low light sensitivity according to their connections to neurones?

Answer 20

Each cone is connected to its single separate neurone
So it’s less likely enough neurotransmitter is released (given low light levels so less stimulation) will reach neurotransmitter threshold to stimulate neurone to send an impulse to the brain

Question 21

Do rods allow colour vision?

Answer 21

NO only see in GREYSCALE

Question 22

Do cones allow for colour vision?

Answer 22

YES

Question 23

What allows the cones to be able to detect colour?

Answer 23

Different light sensitive iodopsin
Red sensitive
Green sensitive
Blue sensitive

Question 24

How do the cones containing colour sensitive iodopsin see in colour?

Answer 24

Each iodopsin has a peak absorption wavelength which gives the iodopsin (in each cone) its name
Many wavelengths can be absorbed by more than 1 type of cone cell
It is the relative extent to each cone is stimulated which determines the brain to recognise what colour we see

Question 25

Visual acuity

Answer 25

Ability to see in detail

Question 26

High visual acuity

Answer 26

High detail seen

Question 27

What photoreceptors allows high visual acuity?

Answer 27

The cones

Question 28

Why do cones allow high visual acuity?

Answer 28

Each cone is connected to its own single separate neurone
So each cone sends separates sets of impulses to the brain in space allowing high detail (high visual acuity)

Question 29

Why do rods allow only low levels of visual acuity?

Answer 29

Several rods are connected to a single neurone
But only 1 set of impulses are sent to the brain (in spite of several rods being stimulated) in space
So lowers visual acuity