Chapter 14 - The Human Eye

Question 1

Definition+function of cornea?

Answer 1

A dome-shaped transparent layer continuous with the sclera. It refracts or bends light rays into the eye.

Question 2

Definition+function of conjunctiva?

Answer 2

A thin, transparent mucus membrane covering the sclera in front. It secrets mucus to keep the eyeball moist.

Question 3

Definition+function of pupil?

Answer 3

A hole in the centre of the iris. It allows light to enter the eye.

Question 4

Definition+function of iris?

Answer 4

A circular sheet of muscles that contains a pigment which gives the eye its color. It consists of two sets of involuntary muscles, circular and radial muscles, which controls the amount of light entering the eyes.

Question 5

What are 3 functions of the eyelid?

Answer 5

1) protects cornea from mechanical damage
2) squinting prevents excessive light from entering the eye and damaging light sensitive tissues
3) blinking spreads tears over the cornea and conjunctiva, wiping dust particles off the cornea

Question 6

What is the function of eyelashes?

Answer 6

Shield the eye from dust particles.

Question 7

What is the function of the tear gland? (3)

Answer 7

It secretes tears to

1) wash away dust particles
2) keep cornea moist for atmospheric oxygen to dissolve, which diffuses into the cornea
3) lubricate conjunctiva, reducing friction when eyelids move

Question 8

What are the three layers of the walls of eyeballs, from outermost to innermost?

Answer 8

Sclera, choroid, retina

Question 9

What is the of sclerotic coat (sclera)?

Answer 9

It is a tough, white outer covering of the eyeball, continuous with the cornea.

Question 10

What is the function of the sclerotic coat? (3)

Answer 10

1) protects delicate inner structures against mechanical injury
2) provides a place for attachment of eye muscles that facilitate eyeball movement
3) maintains shape of eyeball

Question 11

What are 2 functions of the choroid?

Answer 11

1) pigmented black to prevent internal reflection of light
2) contains blood vessels that transport oxygen and nutrients to the eyeball and removes metabolic waste products from the eyeball

Question 12

What are 3 functions of the retina?

Answer 12

1) contains light sensitive cells known as photoreceptors, which consists of “rods” and “cones”
2) photoreceptors are connected to nerve fibres from the optic nerve
3) images are detected and formed here

Question 13

What are 3 functions of cones?

Answer 13

1) it has red, blue and green cones that contains different pigment which absorbs light of different wavelengths
2) works well only in bright light and enable variety of color vision in bright light
3) responsible for formation of sharp images

Question 14

What are the functions of rods? (3)

Answer 14

1) contains a pigment called visual purple which is bleached when exposed to bright light, and impulses cannot be sent to the brain. Visual purple must be reformed for one to see in the dark.
2) stimulated only in very dim light
3) enables us to see in dim light, but only black or white

Question 15

Why is it that one might not be able to see for some time when one moves from a brightly-lit room to a dimly-lit room?

Answer 15

It takes a while for visual purple to be reformed in the rods.

Question 16

What is night blindness?

Answer 16

A person deficient in vitamin A might not be able to see in dim light as the formation of visual purple requires vitamin A.

Question 17

Definition+function of fovea (yellow spot)?

Answer 17

It is a small yellow depression where images are focused, which contains the highest concentration of cones but no rods.
It enables a person to have detailed color vision in bright light.

Question 18

What is the blind spot?

Answer 18

It is the point where optic nerve leaves the eye. It is not sensitive to light as it does not contain photoreceptors.

Question 19

What is the function of optic nerve?

Answer 19

Transmit nerve impulses from retina to brain.

Question 20

Definition+function of lens?

Answer 20

It is a transparent, circular and biconvex structure.

It focuses light onto the retina, and its shape or thickness can be changed in order to refract light onto the retina.

Question 21

What is the suspensory ligament?

Answer 21

It is a connective tissue that attaches lens to the ciliary body.

Question 22

Definition+function of ciliary body?

Answer 22

It is a thickened region at the front end of the choroid.

It contains ciliary muscles which controls the curvature or thickness of the lens by contracting and relaxing.

Question 23

Definition+function of aqueous chamber?

Answer 23

It is the space between the lens and the cornea. It is filled with aqueous humor, a transparent, watery fluid that keeps the front if the eyeball firm and refracts light into the pupil.

Question 24

Definition+function of vitreous chamber?

Answer 24

It is the space behind the lens. It is filled with vitreous humor, a transparent jelly-like substance which keeps the eyeball firm and refracts light onto the retina.

Question 25

What are circular and radial muscles?

Answer 25

They are antagonistic muscles that work together to control the size of the pupil.

Question 26

How does the iris control the amount of light entering the eyes in bright light? (3)

Answer 26

1) the circular muscles of the iris contract
2) the radial muscles of the iris relax
3) the pupil constricts, reducing the amount of light entering the eyes.

Question 27

How does the iris control the amount of light entering the eyes in dim light? (3)

Answer 27

1) circular muscles of the iris relax
2) radial muscles of the iris contract
3) pupil dilates, increasing the amount of light entering the eye.

Question 28

What happens when the light is too bright that decreasing the size of the pupil is insufficient?

Answer 28

Eyelids will close to screen of part of the light, preventing excessive light from entering the eye and damaging the retina.

Question 29

What is the pupil reflex?

Answer 29

It is a reflect action that is a response to change in light intensity. It protects the eye from excessive light exposure that could damage the retina.

Question 30

Describe the path of the reflex arc of the pupil reflex. (6)

Answer 30

1) stimulus (change in light intensity)
2) receptor (retina)
3) sensory neurone in optic nerve
4) relay neurone in brain
5) motor neurone
6) effector (iris)

Question 31

How do we see? (5)

Answer 31

1) when light falls on an object, rays of light are reflected on the object. The light rays fall on the eye, and then refracted through the cornea and aqueous humor onto the lens.
2) the lens cause further refraction and rays are brought to a focus on the retina.
3) the image on the retina stimulates either the rods or cones depending on the intensity of light. Forming a vertically inverted, diminished (smaller) and laterally inverted image.
4) nerve impulses are generated when light falls on the rods and cones. The nerve impulses are transmitted via the optic nerve to the optic centre of the brain
5) the brain interprets the information and forms an upright image.

Question 32

What is the role of brain in vision?

Answer 32

The brain has a corrective function which makes the upside down image on the retina upright.

Question 33

Why does images seem upside down to the blind who just restored their sight?

Answer 33

The brain has to learn how to correct the images that fall on the retina first.

Question 34

Define focusing/accommodation.

Answer 34

It is the adjustment of lens of the eye so that clear images of objects at different distances are formed on the retina.

Question 35

How does focusing work?

Answer 35

The curvature or thickness of the lens is adjusted, allowing light rays to be focused on the retina.

Question 36

What happens when one focuses on a distant object? (6)

Answer 36

1) ciliary muscles relax, pulling on the suspensory ligaments
2) suspensory ligaments become taut, pulling on the edge of the lens
3) lens become thinner and less convex, increasing focal length
4) light rays are sharply focused on the retina, stimulating the photoreceptors, which are the cones and rods
5) nerve impulses generated are transmitted to the brain via the sensory neurone in optic nerve.
6) the brain interprets the impulses and the person sees the distant object.

Question 37

What happens when one focuses on a near object? (6)

Answer 37

1) ciliary muscles contract, relaxing their pull on suspensory ligaments.
2) suspensory ligaments slacken, relaxing their pull on the lens
3) lens become thicker and more convex, decreasing the focal length
4) light rays are sharply focused on the retina, stimulating the photoreceptors, which are the cones and rods
5) nerve impulses generated are transmitted to the brain via the sensory neurone in optic nerve
6) the brain interprets the impulses and the person sees the near object.