eye

Question 1

What is the function of the pupil? (pupil reflex)

Answer 1

It allows light to enter the eye.

Question 2

What is the function of the iris? (pupil reflex)

Answer 2

It contains muscles that control the size of the pupil.

Question 3

What is the function of the ciliary body? (focusing/accommodation)

Answer 3

It contains ciliary muscles which control the curvature / thickness of the lens.

Question 4

What is the function of the suspensory ligament? (focusing/accommodation)

Answer 4

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

Question 5

What is the function of the lens? (focusing/accommodation)

Answer 5

It is a transparent, circular and biconvex structure. It is elastic and changes its shape or thickness in order to focus light onto the retina.

Question 6

What is the function of the retina? (nervous pathway)

Answer 6

It is the innermost layer of the eyeball, images are formed on it (light-sensitive). It consists of photoreceptors (rods and cones) which are connected to the nerve endings from the optic nerve.

Question 7

What is the function of the optic nerve? (nervous pathway)

Answer 7

It is a nerve that transmits nerve impulses to the brain when the photoreceptors in the retina are stimulated.

Question 8

What is the function of the fovea/yellow spot? (nervous pathway)

Answer 8

It is a small yellow depression in the retina, situated directly behind the lens. This is where images are normally focused. It has the greatest concentration of cones, but no rods. It hence enables a person to have detailed colour vision in bright light.

Question 9

What is the function of the blind spot?

Answer 9

It is the region where the optic nerve leaves the eye. It does not contain any rods or cones, therefore it is not sensitive to light.

Question 10

What is the function of the sclera?

Answer 10

It forms a protective layer around the eyeball.

Question 11

What is the function of the aqueous chamber? (refraction)

Answer 11

It is the space between the lens and the cornea, it is filled with aqueous humour (transparent, watery fluid) which keeps the front of the eyeball firm and helps to refract light into the pupil.

Question 12

What is the function of the vitreous chamber? (refraction)

Answer 12

It is the space behind the lens, filled with vitreous humour (transparent, jelly-like substance) which helps to keep the eyeball firm and helps to refract light onto the retina.

Question 13

What is the function of the cornea? (refraction)

Answer 13

It is a dome-shaped transparent layer continuous with the sclera. It refracts/bends light rays into the eye. (It causes most of the refraction of light that occurs in the eye)

Question 14

What is the function of the choroid? (nutrient supply)

Answer 14

It is the middle layer between the sclera and the retina. It is pigmented black to prevent internal reflection, it contains blood vessels that bring oxygen and nutrients to the eyeball and removes metabolic waste products.

Question 15

Pupil reflex: how does the iris behave in bright light?

Answer 15

The circular muscles of the iris contract.
The radial muscles of the iris relax.
The pupil becomes smaller or constricts. This reduces the amount of light entering the eye.

Question 16

Pupil reflex: how does the iris behave in dim light?

Answer 16

The radial muscles of the iris contract.
The circular muscles of the iris relax.
The pupil enlarges or dilates. This increases the amount of light entering the eye.

Question 17

What is the nervous pathway in a pupil reflex?

Answer 17

Stimulus (change in light intensity) –> receptor (retina) –> sensory neurone in optic nerve –> brain –> motor neurone –> effector (iris)

Question 18

How does the eye focus on a distant object?

Answer 18

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 its focal length.
4. Light rays from the distant object are sharply focused on the retina.

Question 19

How does the eye focus on a near object?

Answer 19

1. Ciliary muscles contract, relaxing their pull on the suspensory ligaments.
2. Suspensory ligaments slacken, relaxing their pull on the lens.
3. Lens becomes thicker and more convex, decreasing its focal length.
4. Light rays from the near object are sharply focused on the retina.