Practise The human nervous system. 19 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.
Grade by grade
What you need to be able to do, from the first marks up to the top grade.
3
State what the nervous system doesIt lets you react to your surroundings and coordinates your behaviour.
4
Name the parts of the CNSThe central nervous system (CNS) is the brain and spinal cord.
4
Put the reflex arc in orderStimulus → receptor → sensory neurone → relay neurone → motor neurone → effector → response.
5
Explain why reflex actions are fastThey are automatic and do not involve the conscious part of the brain.
5
Describe the ruler-drop reaction time practicalCatch a dropped ruler, record the distance it fell and convert it to a reaction time.
6
Explain how impulses cross a synapseA chemical is released, diffuses across the gap and binds to receptors on the next neurone, starting a new impulse.
6
Explain how neurones are adaptedLong axons carry impulses a long way, branched endings connect to many neurones, and a fatty sheath speeds impulses up.
7
Analyse and evaluate reaction time dataCalculate means, spot anomalies, judge conclusions and suggest control variables.
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.
Synapses and adaptations
A synapse is the tiny gap where two neurones meet.
When an impulse reaches the end of a neurone, a chemical is released. It diffuses across the gap and binds to receptors on the next neurone, which triggers a new electrical impulse. grade 6+
Neurones have a long axon to carry impulses over long distances, branched endings to connect with many other neurones, and a fatty (myelin) sheath that insulates the axon and speeds up impulses. grade 6+
Required practical: reaction time
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.
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.
Reflex = automatic and rapid; does not involve the conscious part of the brain
Synapse: a chemical is released, diffuses across the gap and binds to receptors on the next neurone grade 6+
Reaction time practical: shorter catch distance = faster reaction
How to answer each type of question
Describe the pathway of a reflex arc
3 to 4 marks5
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.
Show the model answer
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 how an impulse crosses a synapse
3 marks6
The impulse arrives at the end of the first neurone.
A chemical is released and diffuses across the gap.
The chemical binds to receptors on the next neurone, starting a new electrical impulse.
Example. Describe how a nerve impulse passes from a sensory neurone to a relay neurone.
Show the model answer
The impulse reaching the end of the sensory neurone causes a chemical to be released (1). The chemical diffuses across the synapse / gap (1). It binds to receptors on the relay neurone, triggering a new electrical impulse (1).
Explain why a reflex is an advantage
2 marks5
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.
Show the model answer
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).
Required practical: reaction time data
3 to 5 marks6
Spot any anomalous result and leave it out of the mean.
Add the remaining values and divide by how many there are.
Name specific control variables, not just 'keep it fair'.
Example. A student caught a dropped ruler five times. The distances it fell were 14 cm, 12 cm, 13 cm, 25 cm and 11 cm. (a) Identify the anomalous result. (b) Calculate the mean distance, not including the anomalous result. (c) Give two variables the student should control.
Show the model answer
(a) 25 cm (1) (b) (14 + 12 + 13 + 11) ÷ 4 = 50 ÷ 4 (1) = 12.5 cm (1) (c) Any two from: same person dropping the ruler; same hand used to catch; same starting gap between thumb and finger; same ruler (2)
Shortcuts and 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.
Where marks are lost
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.
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.
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.
A person touches a very hot pan and moves their hand away before they feel any pain.
(a) Describe the pathway taken by nerve impulses in this reflex, from the receptor to the effector.[4]
(b) Explain how a nerve impulse passes across a synapse.[2]
(c) Explain why reflex actions are important.[2]
(d) Reflex actions do not involve the conscious part of the brain. Explain why this makes them faster.[1]
Show the answer and mark scheme
(a)
receptors in the skin detect the heat / stimulus
impulses travel along a sensory neurone to the spinal cord / CNS
impulses pass (across a synapse) to a relay neurone in the spinal cord
impulses travel along a motor neurone to the effector / muscle
the muscle contracts, moving the hand away
(b)
a chemical is released by the first neurone
the chemical diffuses across the gap and causes an impulse in the next neurone
(c)
they are automatic and rapid
(so) they protect the body from harm / damage, e.g. burns
(d)
no time is taken to think / decide / fewer neurones and synapses are involved
Question 3Hard7 marks
A student wants to find out whether practice affects reaction time. The student will use the ruler-drop test and a table that converts the distance the ruler falls into a reaction time.
(a) The person dropping the ruler must not warn the catcher before letting go. Give the reason why.[1]
(b) Plan an investigation to find out whether practice affects reaction time.[6]
Show the answer and mark scheme
(a)
so the catcher reacts to seeing the ruler fall (and does not anticipate / react to a sound)
(b)
one person holds a (30 cm) ruler vertically with the zero mark level with the top of the catcher's thumb
the catcher's forearm rests on the edge of a table / hand is in the same position each time
the ruler is dropped without warning and caught as quickly as possible
record the distance the ruler falls and convert it to a reaction time using the table
test the catcher (e.g. 5 times) before practice to get a starting mean
the catcher then practises, e.g. 20 catches, and is tested again (repeat after more practice)
control variables: same catcher, same hand, same ruler, same person dropping, same starting gap, no distractions
calculate a mean for each stage, ignoring anomalous results
compare the mean reaction times before and after practice / plot a graph of reaction time against number of practice catches
Marked with levels of response: the full level descriptors are in the app.