Title: How do our bodies respond to stimili? 28th February 2014

Learning question: How do animals detect stimuli?L.O 2.19 – 2.23

Homework: complete summary sheet for TUESDAY 4th March

Starter: name each part of the neurone below:

Key words…

•Myelin sheath•Synapse•Neurotransmitter

•Reflex arc

Sensory neurone

Relay neurone

Motor neurone

The structure of a neurone• Neurones are very similar

to electrical wires – – they conduct signals very

quickly

– have a layer of insulation to speed up the rate of transmission of that signal

• In neurones, the insulating layer is a fatty substance called a myelin sheath

Myelin sheath

Neurone

The axon endings are the part of the neurone that passes on information to the next neurone in the sequence

Synapses

• Neurones do not actually connect with each other – there are tiny gaps between the end of one and the start of another.

• The gap between two neurones is called a synapse

Synapse• The diagram opposite dhows

part of the reflex arc. How many synapses can you see?

• Impulses in a neurone always travel from dendrite to axon ending.

• So this means the end of one axon will pass on messages to the start of the next dendrite

A

B

Neurotransmitters• Signals cross a synapse using chemicals released

by a neurone.

• The chemical diffuses across the gap makes the next neurone transmit an electrical signal.

1. An electrical impulse travels along an axon.

2. This triggers the nerve-ending of a neuron to release chemical messengers called neurotransmitters.

3. These chemicals diffuse across the synapse (the gap) and bind with receptor molecules on the membrane of the next neuron.

4. The receptor molecules on the second neuron bind only to the specific chemicals released from the first neuron. This stimulates the second neuron to transmit the electrical impulse

1. What is a synapse?

A.A short sleep B.A small gap between nerve cells C.A chemical that transmits nerve signals

2. Which type of neurone transmits a signal from a sense organ to the spinal cord and brain?

A.Sensory B.Relay C.Motor

3. Which type of neurone transmits a signal from the central nervous system to an effector such as a muscle?

A.SensoryB.RelayC.Motor

4. How is a reflex action different from a normal response by the nervous system to a stimulus?

A.It doesn't need to involve the brainB.It doesn't involve the nervesC.It is slower

5. Which of these is not a reflex response?

A.BlinkingB.Picking up a bookC.Sneezing

6. What is the name of the long part of the nerve cell that carries the signal?

A.AxonB.DendronC.Cytoplasm

7. The ability of the eye to control the amount of light entering it is:

A.accommodationB.a reflex actionC.a learned response

15

1 Imagine you see a lion and run away.a Where are the receptor cells that receive the stimulus.

A: Eyes

b What effectors carry out the response?

A: Muscles in legs

16

c Suggest another effector that may be triggered by the shock of seeing the lion.

A:(Adrenal) gland or muscles in another part of the body.

17

2 Do the following carry information to or away from the central nervous system?

a motor neurones

A:Away from the CNS

b sensory neurones

A:To the CNS.

18

3 Jacob has written: ‘An impulse from a neurone travels through a synapse to get to the next neurone.’ Explain why this is not correct.

A:An impulse does not travel across the synapse. Instead it causes the release of neurotransmitter which then causes a new impulse to be generated in another neurone.

4 Why is the blink reflex useful?

A: To stop objects getting into our eyes.

19

5 Draw a table to compare reflex actions with coordinated responses.

A:A suitable table might include some or all of these rows:

20

Reflex actions Coordinated responses

Speed Faster Slower

Automatic? Yes No

Use the brain for processing

No Yes

Use sensory and motor neurones

Yes Yes

6 Why is it important for reflex arcs to have as few synapses as possible?

A: So that impulses travel through them as quickly as possible (synapses between one neurone and the next, slow down the mean speed of impulses).

21

7 You kick a football. Describe how this coordinated response occurs. You should mention neurones and the central nervous system in your answer.

A: A good answer will include the following points:• light from football detected by receptor cells

eyes• impulses sent from sensory neurone to brain• brain processes signals and sees the football• impulses sent to motor neurones in the legs• muscles are effectors and kick the ball.

22

Reflex vs co-ordinated responses

• What is a reflex? • Give an example and describe how it works.

• What is a co-ordinated response?• Give an example and describe how this would

work

• Which is faster and why?