AQA GCSE Combined Science Foundation (8464), Foundation tier · Biology › Homeostasis and response
Practise The human nervous system. 11 exam-style questions plus unlimited generated ones on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
How the nervous system carries information as electrical impulses, how a reflex arc works, and the required practical on reaction time. Expect ordering and labelling questions, 'explain why reflexes are useful', synapse explanations and data questions from the reaction time practical.
Reflex = automatic and rapid; does not involve the conscious part of the brain
Reaction time practical: shorter catch distance = faster reaction
Notes
How the nervous system works
The nervous system lets you react to your surroundings and coordinate your behaviour.
Receptors detect a stimulus. Information passes along nerve cells (neurones) as electrical impulses to the central nervous system (CNS): the brain and spinal cord.
The CNS coordinates the response of effectors: muscles contract or glands secrete hormones.
Reflex actions are automatic and rapid. They do not involve the conscious part of the brain, so no time is spent deciding what to do.
Reflexes protect you from harm, e.g. pulling your hand away from a hot pan or blinking when something flies towards your eye.
Path: stimulus → receptor → sensory neurone → relay neurone (in the spinal cord or brain) → motor neurone → effector → response.
Sensory neurones carry impulses from receptors to the CNS. Relay neurones link sensory and motor neurones inside the CNS. Motor neurones carry impulses from the CNS to effectors.
Reflex arc: receptor → sensory neurone → relay neurone (in spinal cord) → motor neurone → effector. The arrows show the direction of the impulse.
Synapses and adaptations
A synapse is the tiny gap where two neurones meet.
Required practical: reaction time
diagram
Your partner holds a ruler vertically with the zero mark between your thumb and first finger. They drop it without warning and you catch it as quickly as you can.
Reaction time: the further the ruler falls before you catch it, the longer your reaction time.
Record the distance the ruler fell. A shorter distance means a shorter reaction time. Convert distances to times using a conversion table.
Repeat several times and calculate a mean. Then test a factor such as caffeine, practice, tiredness or distraction.
Control variables: same person dropping the ruler, same hand catching, same ruler, same starting gap between finger and thumb, arm resting on the table edge.
How to answer each type of question
Describe the pathway of a reflex arc
3 to 4 marksGrade 5
Start at the receptor and finish at the effector.
Name the three neurones in order: sensory, relay, motor.
Say where the relay neurone is (the spinal cord) and what the effector does.
Example. A person touches a sharp pin and immediately pulls their hand away. Describe the pathway taken by the nerve impulses in this reflex action.
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Receptors in the skin detect the stimulus (1). Impulses travel along a sensory neurone to the spinal cord (1). They pass to a relay neurone in the spinal cord and then to a motor neurone (1). The motor neurone carries impulses to a muscle (the effector), which contracts to pull the hand away (1).
Explain why a reflex is an advantage
2 marksGrade 5
Say that reflexes are automatic and fast because the conscious brain is not involved.
Say how this protects the body in the context given.
Example. Blinking when an object comes towards your eye is a reflex action. Explain why it is an advantage for this response to be a reflex.
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Reflexes are automatic / do not involve the conscious part of the brain, so they are very fast (1). The eye closes before the object hits it, so the eye is protected from damage (1).
Don’t lose marks
Saying the electrical impulse 'jumps' across the synapse. A chemical diffuses across the gap.
Saying the brain decides what to do in a reflex. Reflexes do not involve the conscious part of the brain.
Missing out the relay neurone, or putting the three neurones in the wrong order.
Including an anomalous result when calculating a mean.
Writing 'keep it a fair test' instead of naming a specific control variable.
More tips
Memory tricks
Sensory neurones Send information in to the CNS; Motor neurones make things Move.
Relay neurones relay the impulse across the CNS, like passing the baton in a relay race.
Ruler drop: short distance = short time = quick reactions.
Synapse in three words: chemical, diffuses, receptors.
Exam technique
Use the exact names: receptor, sensory neurone, relay neurone, motor neurone, effector.
For effectors, give the action in context, e.g. 'a muscle in the arm contracts', not just 'the arm moves'.
In reaction time questions, look at the units and give the mean to a sensible number of decimal places.
If asked why a result is anomalous, say it does not fit the pattern of the other results.
What each grade needs
What you need to be able to do, from the first marks up to the top grade.
Grade 3
State what the nervous system doesIt lets you react to your surroundings and coordinates your behaviour.
Grade 4
Name the parts of the CNSThe central nervous system (CNS) is the brain and spinal cord.
Grade 4
Put the reflex arc in orderStimulus → receptor → sensory neurone → relay neurone → motor neurone → effector → response.
Grade 5
Explain why reflex actions are fastThey are automatic and do not involve the conscious part of the brain.
Grade 5
Describe the ruler-drop reaction time practicalCatch a dropped ruler, record the distance it fell and convert it to a reaction time.
Required practical:Reaction time (method, variables and exam tips)
Quick recall
Cover the answers and test yourself. The app has these as flashcards that come back just before you'd forget them.