Investigating reaction timesSpec 2.13, 2.14
The suggested practicals ask you to investigate human responses to external stimuli, reaction times and the speed of transmission of electrical impulses in the nervous system.
- Independent variable: the factor you change, such as hand used, practice or a distraction.
- Control variables: the same person dropping the ruler, the same ruler, the same starting position and the same person catching.
- Repeat several times and calculate a mean. This reduces the effect of random errors and lets you spot anomalous results.
- A reaction time is the time between a stimulus and a response.
Typical results: practice usually makes the response quicker, and distractions usually make it slower.
Mean distance
A student catches a ruler five times. The distances it fell were 20, 17, 15, 14 and 12 cm. Calculate the mean.
- add the results: 20 + 17 + 15 + 14 + 12 = 78
- divide by the number of results: 78 ÷ 5
Answer: 15.6 cm
Quick check
Name the three types of neurone in a reflex arc, in order.
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Sensory neurone, relay neurone, motor neurone.
What does the myelin sheath do?
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It insulates the neurone and speeds up the transmission of impulses.
What is a synapse?
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A gap between two neurones.
How does an impulse cross a synapse?
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A neurotransmitter is released, diffuses across the gap and triggers a new impulse in the next neurone.
Why are reflexes important?
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They are fast and automatic, so they protect the body from harm.