The Nervous System

Question 1

Why do organisms need to respond to stimuli?

Answer 1

In order to survive.

Question 2

What do multicellular organisms need to do with each other first so that they can respond to their environment?

Answer 2

Communicate. As multicellular organisms “evolved”, they developed nervous and hormonal communication systems.

Question 3

What does the nervous system mean for humans?

Answer 3

They can react to their surroundings and coordinate their behaviour.

Question 4

What are the different parts of the nervous system?

Answer 4

1. Central Nervous System (CNS) - In vertebrates (animals with backbones) this consists of the brain and spinal cord only. In mammals, the CNS is connected to the body by sensory neurones and motor neurones.
2. Sensory Neurones - the neurones that carry information as electrical impulses from the receptors to the CNS.
3. Motor Neurones - The neurones that carry electrical impulses from the CNS to effectors.
4. Effectors - All your muscle and glands, which respond to nerve impulses.

Question 5

What can receptors and effectors form part of?

Answer 5

Complex organs.

Question 6

What are receptors?

Answer 6

The cells that detect stimuli.

Question 7

Examples of types of receptors.

Answer 7

Taste receptors on the tongue and sound receptors in the ears.

Question 8

What can receptors form part of?

Answer 8

Larger, complex organs, e.g. the retina of the eye is covered in light receptor cells.

Question 9

What do effectors respond to?

Answer 9

Nervous impulses and bring about a change.

Question 10

What are muscles and glands know as?

Answer 10

Effectors - they respond in different ways. Muscles contract in response to a nervous impulse, whereas glands secrete hormones.

Question 11

Explain the CNS.

Answer 11

It is a coordination centre - it receives information from the receptors and then coordinates a response (decides what to do about it). The response is carried out by effectors.

Question 12

Give an example of the CNS coordinating a response.

Answer 12

A small bird eating some seed:
1. When, out of the corner of its eye, it spots a cat skulking towards it (this is the stimulus).
2. The receptors in the bird’s eye are stimulated. Sensory neurones carry the information from the receptors to the CNS.
3. The CNS decides what to do about it.
4. The CNS sends information to the muscles in the bird’s wings (the effectors) along motor neurones. The muscles contract and the bird flies away to safety.
Stimulus - Receptor - Sensory neurone - CNS - Motor neurone - Effector - Response.