What is the function of the myelin sheath around a neurone?
- To release neurotransmitter
- To speed up the transmission of impulses
- To detect a stimulus
- To join two neurones together
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Answer: B B (1)
Describe how an impulse is passed from one neurone to the next at a synapse.
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- neurotransmitter is released (from the first neurone) into the synapse / gap (1)
- the neurotransmitter diffuses across the gap (1)
- it binds to receptors on the next neurone, which triggers a new electrical impulse (1)
The flow chart shows a reflex arc: stimulus → receptor → neurone X → neurone Y → neurone Z → effector → response. Name neurones X, Y and Z.
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- X: sensory neurone (1)
- Y: relay neurone (1)
- Z: motor neurone (1)
A student caught a falling ruler five times. The table shows the distance the ruler fell on each attempt. Calculate the mean distance.
| Attempt | 1 | 2 | 3 | 4 | 5 |
|---|---|---|---|---|---|
| Distance fallen in cm | 18 | 16 | 15 | 13 | 11 |
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- 18 + 16 + 15 + 13 + 11 = 73 and 73 ÷ 5 (1)
- 14.6 cm (1) correct answer with no working scores 2
The student's ruler-drop results from the previous question were plotted on a scatter diagram of distance fallen against attempt number. Describe the correlation shown and suggest an explanation for it.
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- negative correlation / distance decreases as the number of attempts increases (1)
- practice makes the reaction time shorter / the response quicker (1)
Explain why a reflex action helps to protect the body.
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- it is fast / rapid / automatic / does not involve conscious thought (1)
- so the body responds before (more) damage is done / reduces injury (1)
A person touches a hot object and pulls their hand away. Explain how the structure and function of the neurones and synapses involved allow this reflex to happen.
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| Level | Marks | What the answer does |
|---|---|---|
| 3 | 5–6 | Describes the whole pathway in order, naming receptor, sensory, relay and motor neurones and effector. Explains how synapses transmit the impulse with neurotransmitters and links structure (such as myelin sheath or axon) to function. Scientific terms are used accurately. |
| 2 | 3–4 | Describes most of the pathway in order with the types of neurone named, and mentions synapses or neurotransmitters. Links between structure and function may be missing. |
| 1 | 1–2 | Gives isolated points about neurones or the response, with little order or explanation. |
Indicative content
- receptors in the skin detect the stimulus (heat or pain) and produce electrical impulses
- sensory neurone carries the impulses to the CNS
- synapse between the sensory neurone and the relay neurone: neurotransmitter is released, diffuses across the gap and triggers an impulse
- relay neurone in the spinal cord passes the impulses to the motor neurone
- motor neurone carries the impulses to the effector (a muscle in the arm)
- the muscle contracts and the hand is pulled away
- the myelin sheath insulates the neurones and speeds up the transmission of impulses
- the long axon carries impulses over long distances
- the reflex is fast and automatic because it does not involve conscious thought