The nervous system

Question 1

Function of ciliary muscles.

Answer 1

Ciliary muscles control suspensory liagments.

Question 2

Function of outer cornea

Answer 2

Outer cornea refracts light rays.

Question 3

Function of pupil

Answer 3

Pupil allows light rays to enter the eye.

Question 4

Function of coloured iris

Answer 4

Coloured iris controls the amount of light entering the eye

Question 5

Function of convex lens

Answer 5

Convex lens refracts light rays and focuses light onto the retina.

Question 6

Light and the retina

Answer 6

A focused image forms on the retina, which is sensitive to light

Question 7

Function of optic nerve

Answer 7

Optic nerve carries nerve impulses to the brain.

Question 8

Function of suspensory ligaments

Answer 8

Suspensory ligaments alter the shape of the lens in focusing.

Question 9

Why is binocular vision useful?

Answer 9

Binocular vision helps to judge distance by comparing the images from each eye; the more different they are, the nearer the object.

Question 10

What is accomodation?

Answer 10

The eye can focus light from distant or near objects by altering the shape of the lens. This is called accommodation.

Question 11

How does the eye focus on distant objects?

Answer 11

To focus on distant objects, the ciliary muscles relax, and the suspensory ligaments tighten, so the lens has a less rounded shape.

Question 12

How does the eye focus on near objects?

Answer 12

To focus on near objects, the ciliary muscles contract, and the suspensory ligaments slacken, so the lens has a more rounded shape due to its elasticity.

Question 13

What causes red-green colour blindness?

Answer 13

A lack of specialised cells in the retina.

Question 14

Cause of long and short sightedness?

Answer 14

• Long and short sight are caused by the eyeball or lens being wrong shape.
• In long sight, the eyeball is too short or the lense is too thin, so the image is focused behind the retina.
• In short sight, the eyeball is too long or the lens is too rounded, so the image would be focused in front of the retina.

Question 15

How is long and short sightedness corrected?

Answer 15

• Corneal surgery or a lens in glasses or contact lenses correct long and short sight.
• A convex lens is used to correct long sight.
• A concave lens to correct short sight.

Question 16

What causes red-green colour blindness?

Answer 16

A lack of specialised cells in the retina.

Question 17

What are nerve cells called?

Answer 17

Neurons

Question 18

Where do nerve impulses pass along?

Answer 18

Nerve impulses pass along the axon.

Question 19

A reflex action is shown by a reflex arc. The links in a reflex arc are:

Answer 19

stimulus→receptor→sensory neurone→central nervous system→motor→effector→response

Question 20

The pathway for a spinal reflex is:

Answer 20

receptor→sensory neurone→relay neurone→motor→effector

Question 21

How are neurones adapted?

Answer 21

• Neurones are adapted by being long,
• having branched endings (dendrites) to pick up inpulses
• and having an insulator sheaf.

Question 22

What is the synapse and what hapens at it?

Answer 22

The gap between neurones is called a synapse. The arrival of an impulse triggers the release of a transmitter substance, which diffuses across the synapse. The transmitter substance binds with receptor molecules in the membrane of the next neurone causing the impulse to continue.