eye

Question 1

what makes up the external structure of the eye

Answer 1

sclera, conjunctiva, eyelashes, tear gland, eyelids, iris, pupil

Question 2

what is the sclera

Answer 2

tough, white outer covering of eyeball that protects the eye from mechanical damage

Question 3

what is the conjunctiva

Answer 3

thin, transparent membrane covering the sclera and secretes mucus to keep the eye moist

Question 4

what is the iris

Answer 4

a circular sheet of muscles that controls the size of the pupils and amount of light entering the eye

Question 5

what is the pupil

Answer 5

hole in the centre of the eye that allows light to enter

Question 6

function of the eyelashes

Answer 6

shields eyes from dust particles

Question 7

function of tear gland

Answer 7

secretes tears that wash away dust particles, keep cornea moist for oxygen to diffuse into, lubricate conjunctiva to reduce friction when eyelids move

Question 8

function of eyelids

Answer 8

protect cornea from mechanical damage, blinking spreads tears over cornea and conjunctiva, wipes dust particles off cornea

Question 9

what makes up the internal structure of the eye

Answer 9

11. retina, lens, blind spot, optic nerve, fovea, vitreous chamber, choroid, ciliary body, suspensory ligament, cornea, aqueous humour

Question 10

what is the retina

Answer 10

the innermost, light-sensitive layer of the eyeball on which images are formed. contains photoreceptors like rods and cones

Question 11

what are the lens

Answer 11

transparent, circular, biconvex structure that changes shape or thickness to focus light onto the retina

Question 12

what is the blind spot

Answer 12

region where optic nerve leaves the eye that does not contain rods or cones

Question 13

what is the fovea

Answer 13

small yellow depression in the retina directly behind the lens and allows detailed colour vision in bright light. area where images are normally focused, contains highest concentration of cones but no rods

Question 14

what is the vitreous chamber

Answer 14

space between lens filled with vitreous humour which keeps the eyeball firm and helps refract light onto the retina

Question 15

what is the choroid

Answer 15

middle layer of eyeball, pigmented black to prevent internal reflection of light, contains blood vessels that bring oxygen and nutrients and remove metabolic waste products

Question 16

what is the ciliary body

Answer 16

thick region at front of choroid, contains ciliary muscles that control thickness and curvature of lens

Question 17

what is the suspensory ligament

Answer 17

connective tissue attaching edge of lens to ciliary body

Question 18

what is the cornea

Answer 18

dome shaped transparent layer at the front of the eye that refracts light rays into the eye

Question 19

what is aqueous chamber

Answer 19

space between lens and cornea that is filled with aqueous humour to keep the front of the eyeball firm and refract light into the pupil

Question 20

function of cones and rods

Answer 20

cones: enable us to see colours in bright light
rods: enable us to see in black and white in dim light

Question 21

what is pupil reflex

Answer 21

automatic adjustment of size of pupil when light intensity changes to ensure the right amount of light enters the eye

Question 22

how does pupil reflex work

Answer 22

1. when light intensity is high, circular muscles contract and radial muscles relax, causing pupils to constrict and less light to enter the eye
2. when light intensity is low, radial muscles contract and circular muscles relax, causing pupil to dilate and more light to enter eye

Question 23

benefits of pupil reflex

Answer 23

1. automatic and immediate
2. prevents excessive light from damaging retina
3. allows enough light to enter eye for us to see

Question 24

nervous pathway in pupil reflex

Answer 24

1. light ray is refracted onto retina
2. receptors in retina are stimulated
3. sensory neurone in optic nerve transmits nerve impulses to brain
4. nerve impulse transmitted to relay neurone in brain
5. motor neurone transmits nerve impulses from brain to iris
6. iris muscles contract and relax accordingly depending on light intensity

Question 25

how do we see

Answer 25

1. light rays from an object are refracted through the cornea and aqueous humour onto the lens
2. lens cause further refraction and rays are brought to focus on the retina
3. image on the retina stimulates either rods or cones, and is upside down, laterally inverted and diminished
4. nerve impulses are produced and transmitted to the brain where they are interpreted such that we see the object right side up, front to back and the right size

Question 26

what is focusing / accommodation

Answer 26

adjustment of the thickness and curvature of the lens so that clear images of objects are formed on the retina

Question 27

process of focusing on distant object (>7m)

Answer 27

since object is far away, reflected light rays that reach the eye are almost parallel to each other
1. ciliary muscles relax, pulling on suspensory ligaments
2. suspensory ligaments become taut, pulling on the edge of the lens
3. lens become thinner and less convex
4. light rays from object are sharply focused on the retina
5. photoreceptors are stimulated
6. nerve impulses are produced and transmitted and brain interprets image correctly

Question 28

process of focusing on nearby object

Answer 28

when looking at near object, light rays reflected are diverging and lens need to be thicker to bend them more
1. ciliary muscles contract, relaxing pull on suspensory ligaments
2. suspensory ligaments slacken, relaxing pull on lens
3. elastic lens become thicker and more convex
4. light rays from nearby object are sharply focused onto retina
5. photoreceptors are stimulated
6. nerve impulses are produced and transmitted to the brain and interpreted correctly