B3.1 The Nervous System - Eye

Question 1

Describe and state the function of the cornea.

Answer 1

• Transparent coating on the front of the eye
• Protects the eye, refects light entering the eye

Question 2

Describe and state the function of the conjunctiva.

Answer 2

• Protective membrane contiunuous with the eyelids across the front of the visible sclera
• Protects from infection by stopping pathogens entering the eye

Question 3

Describe and state the function of the pupil.

Answer 3

• Central hole in the iris
• Allows light to enter the eye

Question 4

Describe and state the function of the iris.

Answer 4

• Coloured ring of muscle
• Alters pupil size by contracting or relaxing

Question 5

Describe and state the function of the lens.

Answer 5

• Transparent biconvex lens
• Focuses light clearly onto the retina

Question 6

Describe and state the function of the suspensory ligaments.

Answer 6

• Work together with the cilary body to control the shape of the lens by becoming taught or slack
• Connect the ciliary body to the lens
• When ciliary muscles contract the suspensory ligaments relax allowing the lens to go fat
• When ciliary muscles relax the suspensory ligaments are pulled taught stretching the lens thinner

Question 7

Describe and state the function of the retina.

Answer 7

• Contains two types of photoreceptor cells rods and cones
• Photoreceptor cells produce a nervous impulse when exposed to light

Question 8

Describe and state the function of the optic nerve.

Answer 8

• Nervous tissue
• Carries nerve impulse from the retina to the brain

Question 9

Label the parts of the eye

Answer 9

1. Sclera – Tough outer wall, ‘white’
2. Conjunctiva – membrane over eye
3. Cornea – transparent outer layer
4. Lens – focuses light
5. Pupil – allows light into eye
6. Aqueous humor - nutrients & pressure
7. Iris – controls diameter of pupil via circular and radial muscles
8. Vitreous humor – pressure and shape.
9. Choroid – nutrients & waste
10. Fovea – blind spot
11. Optic nerve head – nerves exit
12. Optic nerve – impulses to eye
13. Retina – contains rods & cones

Question 10

What is the aqueous humor

Answer 10

A fluid which is between the cornea and lens that provides nutrients for the the lens and cornea that have no blood supply and helps maintain pressure

Question 11

What is the vitreous humor?

Answer 11

A transparent, colourless, gel-like substance that fills the space between the lens and the retina within the eye and helps maintain pressure and shape.

Question 12

Name the two types of photo receptor cell in the eye.

Answer 12

1. Rods - respond to light and allow you to see in low light levels
2. Cones - respond to red, blue and green light to allow you to see in different colours

Question 13

Name the cells and their structures.

Answer 13

Cell A: Rod cell

Cell B: Cone cell

1. Outer segment
2. Inner segment
3. Synaptic region
4. Disc
5. Connecting cillium
6. Mitochondria
7. Nucleus
8. Synapse

Question 14

How do the circular and radial muscles control the size of the pupil?

Answer 14

1. In dim light the radial muscles contract and the circular muscles relax to make the pupil become larger to allow more light to reach the retina.
2. In bright light the radial muscles relax and the circular muscles contract to make the pupil become smaller and protect the retina.

Question 15

How do the suspensory ligaments and cilliary muscles control the shape of the lens?

Answer 15

1. When an object is nearby the cilliary muscle contracts down towards the lens allowing the suspensory muscles to become slack. This causes the lens to fatten and become more convex, increasing the refraction of the light passing through.
2. When an object is far the cilliary muscle relaxes away from the lens allowing the pulling the suspensory muscles taut. This causes the lens to be pulled thiner and become less convex, decreasing the refraction of the light passing through.

Question 16

What is the name given to the process of focusing incoming light?

Answer 16

accomodation

Question 17

What is meant by the term myopia?

Answer 17

• Shortsightedness
• Someone who is short-sighted can see near objects clearly, but they cannot focus properly on distant objects.

Question 18

Name the causes of myopia?

Answer 18

1. Eyeball elongated = distance the lens to retina too great
2. Lens too thick and curved = light is refracted to much and focuses short

Question 19

How can myopia be corrected?

Answer 19

Myopia is corrected by a concave lens in front of the eye.

Question 20

What is meant by the term hyperopia?

Answer 20

• Longsightedness
• Someone who is long-sighted can see distant objects clearly, but they cannot focus properly on near objects.

Question 21

What are the causes of hyperopia?

Answer 21

• Eyeball too short = distance the lens to retina too small
• Loss of elasticity in the lens = cannot become thick enough to focus (often age-related)

Question 22

How can hyperopia be treated?