human eye

Question 1

function of eyelid

Answer 1

-protect cornea from excessive damage
-closing eye to prevent excessive light from entering
-blinking spread tears over the eyes so dust is wiped off

Question 2

function of eyelashes

Answer 2

-shield eye from dust particles

Question 3

function of tears

Answer 3

-washes away dust particles
-keep the cornea moist for atmospheric oxygen to dissolve
-lubricates conjunctiva, reduce friction when eyelid moves

Question 4

function of cornea

Answer 4

-dome shaped transparent layer to bend or refract light rays into eyes

Question 5

function of iris

Answer 5

-circular sheet of muscles that contain pigment that gives eye colour
-controlled by circular and radial involuntary muscles

Question 6

function of pupil

Answer 6

-hole in center of eye that allows light to enter

Question 7

function of conjunctiva

Answer 7

-mucus membrane that covers sclera,
-sclera secretes mucus to keep front of eyeball moist

Question 8

what is the sclera

Answer 8

-tough white outer covering of the eyeball
-continuous of cornea

Question 9

function of lens

Answer 9

-transparent circular biconvex structure that change shape and thickness to refract light into retina

Question 10

function of ciliary body

Answer 10

-contains ciliary muscles that controls the curvature and thickness of lens

Question 11

function of suspensory ligament

Answer 11

-ligaments that attach edge of lens to ciliary body

Question 12

function of choroid

Answer 12

-black pigmented middle layer of eyeball that prevents internal reflection of light
-contains blood vessels to carry oxygen and nutrients to eyeball while removing carbon dioxide and waste products

Question 13

what is vitreous humour and where is it found

Answer 13

-transparent jelly like substance that keeps eyeball firm and reflects light to retina
-in vitreous chamber, space behind lens

Question 14

what is aqueous humour and where is it found

Answer 14

-transparent water like substance that keeps front of pupil firm and refract light into pupil
-in aqueous chamber, space between cornea and lens

Question 15

function of retina

Answer 15

-contains photoreceptors, light sensitive cell that has rods and cones

Question 16

what is fovea/yellow spot

Answer 16

-small yellow depression where images are not focused
-contains cones but no rods, cones are for colour vision, rods are for seeing in the dark
-more detail colour vision in bright light

Question 17

function of optic nerve

Answer 17

-nerve that transmit nerve impulses to brain upon stimulation of photoreceptors

Question 18

what is blind spot

Answer 18

-region where optic nerve leaves the eye
-absence of rods and con so sensitivity to light

Question 19

what is the pupil reflex

Answer 19

-reflex action involving receptors and effectors that occurs as a result of changes in light intensity

Question 20

process of pupil reflex

Answer 20

-stimulus, change in light intensity
-receptors within the retina
-sensory neurone in optic nerve sends nerve impulses to brain
-nerve impulses from brain to motor neurone
-to effecters, iris

Question 21

how does iris control the amount of light entering our eyes

Answer 21

-iris controlled by two sets of involuntary radial and circular muscles that work antagonistically
-Bright light, circular muscle contract, pupil constrict, reduce amount of light entering eyes
-dim light, radial muscle contracts, pupils dilate, increase amount of light entering eyes

Question 22

what is the formation of image in retina

Answer 22

-light rays are refracted when it passes through the cornea and aqueous humour
-light rays further refracted when it passes through the lens
-image in retina is stimulates either rods or cones depending on intensity of light
-image formed on retina usually inverted, laterally inverted and smaller than in size than real object

Question 23

what is the role of brain in vision

Answer 23

-the image is made upside down by the retina, brain makes it upright
-brain contains corrective function
-when blind people’s sight restores, objects appear upside down to them at first before brain learns how to correct it

Question 24

what is focusing and how is it done

Answer 24

-adjustment of lens of the eye so that clear images of objects at different distance are formed in retina
-adjustment of thickness or curvature of lens
-allows light rays to focus on retina, enabling a clear image in retina to be formed

Question 25

how to focus on distant object

Answer 25

-ciliary body relax, pulling on suspensory ligaments
-suspensory ligaments become taunt, pulling on edge of lens
-lens become thinner and less convex, increasing focal length, distance between middle of lens to point of focus on retina
-light rays focus on retina
-photoreceptors are stimulated, nerve impulses transmitted to brain, interpreted by the brain that allows person to see object

Question 26

how to focus on near object

Answer 26

-ciliary body contracts, relaxing pull on suspensory ligaments
-suspensory ligaments slacken, lessening pull on edge of lens
-lens become thicker and more convex, decreasing focal length
-light rays focus on retina
-photoreceptors stimulated, nerve impulses transmitted to brain, interpreted by the brain that allows person to see object

Question 27

properties of rods

Answer 27

-more sensitive to light than cones
-enable vision in dim light in black and white
-pigment visual purple, gets bleached when exposed to bright light, nerve impulses cannot be sent to brain, hence person has no vision in bright light
-time taken for visual purple to reform in rods before we can see in the dark, hence cannot see for some time from bright lighted room to dimly lit room
-formation of visual purple required vitamin A, night blindess affect vitamin A deficiency

Question 28

properties of cones

Answer 28

-enable us to see colours in bright light
-red blue and green cones each absorb light of different wavelengths and together enable us to see a variety of colours, do not work well in dim light

Question 29

what is colour blindness

Answer 29

-person is not able to perceive certain colours, of the three basic cones that allow us to see the three basic colours is missing