Eye receptors

Question 1

Photoreceptors

Answer 1

Receptors in the eye which detect light

Question 2

Light enters the eye through the …….

Answer 2

Pupil

Question 3

The amount of light that enters the eye is controlled by the ….. …… …… ….

Answer 3

muscles of the iris

Question 4

Light rays are focused by the ….. onto the …..

Answer 4

lens onto the retina

Question 5

Retina

Answer 5

lines the inside of the eye, contains the photoreceptor cells

Question 6

Fovea

Answer 6

An area of the retina where there are lots of photoreceptors

Question 7

Nerve impulses from the photoreceptors are carried from the retina to the brain via the ….. ….

Answer 7

Optic nerve

Question 8

what is the optic nerve made of?

Answer 8

a bundle of neurones

Question 9

Blind spot

Answer 9

where the optic nerve leaves the eye, called this as there are no photoreceptors there - not sensitive to light

Question 10

How photoreceptors work

Answer 10

• light enters eye
• hits photoreceptors + absorbed by light-sensitive optical pigaments (rods = rhodopsin cones = iodopsin)
• light bleaches the pigaments - causing a chemical change + altering the permeability to sodium ions
• generator potential is created + reaches threshold
• nerve impulse sent along bipolar neurone
• bipolar neurone connects photoreceptors to optic nerve which takes impulse to the brain

Question 11

Rod cells - where found + what wavelength sensitive to

Answer 11

• found in peripheral parts of retina
• different optical pigaments (to cone cells) makes them sensitive to different wave lengths of light - only give info in black and white (monochromatic vision)

Question 12

Rod cells - sensitivity

Answer 12

Very sensitive to light (work well in dim light) due to many rods join to one bipolar neurone - so many weak generator potentials combine to reach the threshold + trigger an action potential

Question 13

Rod cells - visual acuity

Answer 13

Low visual acuity as many rods join the same bipolar neurone - means light from two points close together cant be told apart

Question 14

Cone cells - where found + what wavelength of light sensitive to

Answer 14

• found packed in the fovea
• give info in colour (trichromatic vision)
• There are 3 different types of cones containing different optical pigament - red sensitive, green sensitive, blue sensitive - when stimulated in different proportions you see different colours

Question 15

Cone cells - sensitivity

Answer 15

low sensitivity - work best in bright light - due to one cone joins one bipolar neurone - so takes more light to reach threshold to trigger action potential

Question 16

Cone cells - visual acuity

Answer 16

High visual acuity - as cones are close together + one cone joins one bipolar neurone - when light from 2 points hits 2 cones, 2 action potentials go to the brain - so you can distinguish 2 points that are close together as 2 separate points