B1d - the nervous system

Question 1

Name the main parts of the eye and uses (7)

Answer 1

Cornea -refracts light

Iris - controls how much light enters pupil

Pupil

Lens - focuses light on to retina

Retina - contains light receptors, some sensitive to light of different colours

Optic nerve - carries impulses to the brain

Blind spot

Question 2

Describe the pathway of light through the eyeball(2)

Answer 2

Cornea refracts light into the eye

The lens also refracts the light, focusing it onto the retina

Question 3

What is accommodation

Answer 3

Changing the shape of the elastic lens to focus light from distant or near objects

Question 4

How does the eye focus light from near objects(3)

Answer 4

The ciliary muscle contracts

The suspensory ligaments slackens

The lens becomes a more rounded shape, so light is refracted more

Question 5

How does the eye focus light from distant objects(3)

Answer 5

The ciliary muscle relaxes

The suspensory ligaments to pull tight

This pulls the lens into a less rounded shape so light is refracted less

Question 6

Advantages and disadvantages of binocular vision(4)

Answer 6

Better judgement of distance

• compares the images from each eye
• the more similar the images, the further away the object

Narrower field of view

Question 7

Explain a cause of red-green colour blindness

Answer 7

Caused by the lack of specialised cells in the retina

Question 8

What causes long-sightedness

Answer 8

Lens is the wrong shape and doesn’t bend the light enough or the eyeball is too short

Question 9

What causes short-sightedness

Answer 9

The lens is the wrong shape and bends the light too much or the eyeball is too long

Question 10

How can long/short sight be corrected(3)

Answer 10

For long-sighted people - Can use glasses or contact lenses with a convex lens

For short-sighted people - can use glasses or contact lenses with a concave lens

An alternative to glasses/contact lenses is to have corneal laser surgery

Question 11

Name and locate the parts of a motor neurone(3)

Answer 11

Cell body - surrounding the nucleus

Axon- extends from the cell body

Sheath - surrounds the axon

Question 12

Explain how neurones are adapted to their function

Answer 12

Branched endings (dendrites) so they can connect with lots of other neurones

Sheath along the axon that acts as an electrical insulator, which speeds up the electrical impulse

Long, which also speeds up the impulse
-connecting with another neurone slows the impulse down, so 1 long neurone is much quicker than lots of short ones joined together

Question 13

Describe a reflex arc(7)

Answer 13

Stimulus → receptor → sensory neurone → central nervous system → motor neurone → effector → response.

Question 14

Describe the path taken by a spinal reflex(3)

Answer 14

1. A stimulus is detected by a receptor cell, which synapses with a sensory neurone
2. The sensory neurone carries the impulse from site of the stimulus to the central nervous system (spinal cord), where it synapses with an relay neurone
3. The relay neurone synapses with a motor neurone, which carries the nerve impulse out to an effector, such as a muscle, which responds by contracting

Question 15

Which part of the neurone do nerve impulses pass along

Answer 15

Axon

Question 16

What is the gap between neurones called

Answer 16

Synapse

Question 17

Describe what happens in a synapse(3)

Answer 17

1. An impulse triggers the release of a transmitter substance in a synapse
2. Transmitter substance diffuses across the synapse
3. Transmitter substances binds with receptor molecules in the membrane of the next neurone causing the impulse to continue