The human nervous system — AQA GCSE Combined Science
Test yourself on The human nervous system with AQA GCSE practice questions.
7 days Premium · Then free forever · No card, no charge
The human nervous system explained
The nervous system carries information quickly between receptors and effectors.
Read the full explanation
Its structure matches this job. Sensory neurones run from receptors to the central nervous system, which is the brain and spinal cord; relay neurones connect within it; motor neurones carry impulses to effectors. Neurones are long so a single cell spans a distance, have branched endings to connect with many cells, and are insulated by a myelin sheath that speeds up impulse transmission. The spinal cord is a bundle of neurones protected by vertebrae, and reflex arcs pass through it so responses can occur without conscious brain processing. This makes reactions fast and automatic, which reduces harm.
The nervous system enables humans to react to their surroundings and to coordinate their behaviour.
The nervous system is a rapid communication network that detects changes in the internal and external environment and produces coordinated responses. Receptors, such as temperature receptors in the skin or light receptors in the retina, detect a stimulus. This information travels as electrical impulses along neurones to the central nervous system, which processes it and triggers a response by effectors. For example, touching a hot object is detected by receptors in the hand; impulses travel to the spinal cord, which coordinates a rapid withdrawal of the hand by muscles. This coordination allows humans to avoid danger, maintain internal conditions and carry out complex behaviours. The nervous system therefore links detection of a stimulus to a response, and its speed and specificity make it essential for survival.
Information from receptors passes along cells (neurones) as electrical impulses to the central nervous system (CNS). The CNS is the brain and spinal cord. The CNS coordinates the response of effectors which may be muscles contracting or glands secreting hormones.
Receptors detect a stimulus and generate electrical impulses that travel along neurones to the central nervous system. The CNS consists of the brain and spinal cord. The brain processes information and coordinates complex responses, while the spinal cord relays information and coordinates many rapid reflex actions. Once the CNS has processed the information, it sends impulses along motor neurones to effectors. An effector is either a muscle, which responds by contracting, or a gland, which responds by secreting hormones or other substances. For example, if the skin detects a sharp object, impulses travel to the spinal cord, which coordinates a muscle contraction to withdraw the hand. This pathway allows rapid, coordinated responses that protect the body and maintain internal conditions.
stimulus receptor coordinator effector response
A change in the surroundings is a stimulus. A receptor, such as a temperature receptor in the skin or a light receptor in the retina, detects it and generates an electrical impulse. The coordinator, typically the brain or spinal cord, processes the information and decides the response. The effector, a muscle or a gland, then carries out the action. For example, touching a hot beaker: thermoreceptors in the skin detect the heat, sensory neurones carry impulses to the spinal cord, which coordinates a rapid response, and the arm muscle contracts to pull the hand away. This sequence is the basis of both voluntary and reflex pathways, and you must be able to place each component in order and explain its role.
Students should be able to explain how the various structures in a reflex arc – including the sensory neurone, synapse relay neurone and motor neurone – relate to their function. Students should understand why reflex actions are important.
A reflex arc begins when a receptor detects a stimulus and a sensory neurone carries the impulse to the central nervous system. The sensory neurone has a cell body beside the spinal cord and a long dendron, allowing rapid transmission. At a synapse, the impulse triggers release of a neurotransmitter that diffuses across the gap and stimulates the next neurone. A relay neurone inside the spinal cord links the sensory and motor neurones, and the motor neurone carries the impulse to an effector, such as a muscle, which contracts. Reflex actions are automatic and do not involve conscious thought, so they are rapid and protect the body from harm.
Reflex actions are automatic and rapid; they do not involve the conscious part of the brain.
A reflex action is a fast, involuntary response that protects the body from harm. A receptor detects a stimulus, such as heat or a sharp object, and generates an electrical impulse. The impulse travels along a sensory neurone to a relay neurone in the spinal cord or an unconscious region of the brain. The relay neurone passes the impulse to a motor neurone, which carries it to an effector, such as a muscle or gland. The muscle contracts or the gland secretes, producing the response. Because the pathway does not pass through the conscious part of the brain, no decision-making delay occurs, so the response is automatic and rapid. For example, touching a hot surface triggers a withdrawal reflex that moves the hand away before the pain is consciously felt.
Students should be able to extract and interpret data from graphs, charts and tables, about the functioning of the nervous system.
Extracting and interpreting data about the nervous system means reading values accurately from graphs, charts and tables, then using those values to describe or explain nervous function. For example, a graph may show reaction time in milliseconds against a stimulus such as a sound or light. You read the value on the y-axis for a given x-axis value, compare values between conditions, and identify patterns such as a shorter reaction time after practice. You may also calculate a mean from repeated measurements or identify anomalous results. Interpretation goes beyond reading numbers: you link the data to nervous system processes, such as faster impulse transmission or improved coordination, and evaluate whether the evidence supports a conclusion. Always quote units and refer to the data in your answer.
Students should be able to translate information about reaction times between numerical and graphical forms.
Reaction time is the interval between a stimulus and the response it triggers, measured in seconds or milliseconds. In a ruler-drop test, the distance a ruler falls before being caught represents the reaction time. Data from repeated trials can be recorded in a table, and mean reaction times for different conditions can be displayed on a bar chart. Alternatively, a line graph can show reaction time against a continuous variable, such as caffeine intake or time of day. Translating between forms means reading values accurately from a graph, plotting a table of means correctly, and describing the trend or comparison the graph reveals.
Required practical activity 6: plan and carry out an investigation into the effect of a factor on human reaction time.
In this required practical, a ruler-drop test measures reaction time: a partner holds a ruler vertically between your thumb and finger, releases it without warning, and you catch it as quickly as possible. The distance fallen, s, converts to time using t = √(2s ÷ g). You choose one independent variable, such as caffeine intake, time of day, handedness or background noise, and control others including the same ruler, the same release height, the same hand and the same person catching. Repeat each condition several times, discard anomalies, and compare means. A valid plan states the hypothesis, identifies variables, describes a safe and repeatable procedure, and explains how results will be recorded and analysed.
Your focus
- Describe the roles of sensory, relay and motor neurones in a reflex arc.
- Relate neurone features such as length, branching and myelin to their functions.
- Explain how the spinal cord and reflex arc produce rapid, protective responses.
Show all 27 objectives
- State that receptors detect stimuli and effectors produce responses.
- Describe how electrical impulses travel along neurones to coordinate behaviour.
- Explain how nervous coordination enables humans to react rapidly to their surroundings.
- Identify the brain and spinal cord as the components of the CNS.
- Describe how electrical impulses pass from receptors along neurones to the CNS.
- Explain how the CNS coordinates responses of muscles and glands.
- State the correct order of the components in a stimulus–response pathway.
- Identify the receptor, coordinator and effector in a named example.
- Explain the role of each component in producing a response.
- Describe the pathway of a reflex arc from receptor to effector.
- Explain how the structure of each neurone and the synapse relates to its function.
- Explain why reflex actions are rapid and important for protection.
- Describe the components of a reflex arc in the correct sequence.
- Explain why reflex actions are automatic and rapid, referring to the absence of conscious brain involvement.
- Identify the roles of sensory neurones, relay neurones, motor neurones and effectors in a named reflex action.
- Extract accurate values from graphs, charts and tables about nervous system function.
- Interpret patterns and trends in nervous system data, quoting values and units.
- Use data to support or evaluate conclusions about nervous system function.
- Read and interpret reaction-time values from tables, bar charts and line graphs.
- Plot reaction-time data accurately on appropriate axes.
- Describe the trend or comparison shown in graphical representations of reaction times.
- Design a valid ruler-drop investigation with a clear independent variable and controlled variables.
- Carry out the procedure safely and record distance and time data accurately.
- Analyse repeated measurements by calculating means and comparing reaction times between conditions.
The human nervous system exam tips
Marking Points
- Links sensory neurones to receptors and the central nervous system, and motor neurones to effectors.
- Explains that relay neurones connect sensory and motor neurones inside the central nervous system.
- Uses neurone length and branched connections to explain rapid communication across the body.
- Explains that the myelin sheath insulates the axon and increases the speed of impulse transmission.
- Explains that the spinal cord and reflex arc allow rapid, automatic responses that reduce injury.
- Receptors detect stimuli in the surroundings or inside the body.
- Electrical impulses travel along neurones to the central nervous system.
- The central nervous system coordinates the response.
- Effectors such as muscles or glands carry out the response.
- Coordination allows rapid, appropriate reactions that help humans survive and function.
- Receptors detect stimuli and initiate electrical impulses.
- Impulses travel along neurones to the central nervous system.
- The CNS is made up of the brain and spinal cord.
- The CNS coordinates responses by sending impulses to effectors.
- Effectors are muscles, which contract, or glands, which secrete hormones.
- A stimulus is a detectable change in the internal or external environment, such as a change in temperature, light intensity or pressure.
- A receptor is a specialised cell or structure that detects the stimulus and converts it into an electrical impulse in a neurone.
- The coordinator is the brain or spinal cord; it receives impulses, processes information and determines the appropriate response.
- An effector is a muscle or gland that responds to the impulse, either by contracting or by secreting a substance.
- The response is the resulting change in the organism, such as movement away from a harmful stimulus.
- The sequence is stimulus → receptor → coordinator → effector → response, and each stage must be linked to a named example.
- The sensory neurone carries impulses from receptors to the central nervous system and has a cell body positioned alongside the spinal cord.
- The relay neurone is located inside the spinal cord or brain and connects the sensory neurone to the motor neurone.
- The motor neurone carries impulses from the central nervous system to an effector, such as a muscle or gland.
- At a synapse, a neurotransmitter is released from the presynaptic neurone, diffuses across the synaptic gap and binds to receptors on the postsynaptic neurone.
- Reflex actions are rapid and automatic because the pathway does not pass through the conscious areas of the brain.
- Reflex actions are important because they protect the body from damage, for example withdrawing a hand from a hot object or blinking in response to a bright light.
- A reflex action is automatic and rapid because the impulse pathway does not involve the conscious part of the brain.
- A receptor detects the stimulus and initiates an electrical impulse in a sensory neurone.
- The impulse is passed from the sensory neurone to a relay neurone in the spinal cord or an unconscious region of the brain.
- The relay neurone passes the impulse to a motor neurone, which carries it to an effector such as a muscle or gland.
- The effector produces the response, for example a muscle contracts to withdraw a hand from a hot surface.
- The reflex arc is the receptor–sensory neurone–relay neurone–motor neurone–effector pathway.
- Conscious thought is not required, so the response is faster than a voluntary reaction that involves decision-making in the conscious brain.
- Read values accurately from the axes of a graph or from cells in a table, including correct units such as milliseconds (ms) or metres per second (m/s).
- Identify the independent variable and dependent variable in a data set about nervous function.
- Describe patterns or trends, such as reaction time decreasing as a stimulus becomes more intense or after repeated trials.
- Compare data between conditions or groups, quoting specific values to support the comparison.
- Calculate a mean from repeated measurements and identify anomalous results that do not fit the pattern.
- Interpret data in terms of nervous system function, for example linking a shorter reaction time to faster impulse transmission or more efficient coordination.
- Evaluate whether the data support a stated conclusion, recognising limitations such as small sample size or uncontrolled variables.
- Identify the stimulus and the response in a described reaction-time test, stating that reaction time is measured in seconds or milliseconds.
- Read a value from a plotted graph, including interpolating between labelled gridlines and stating the unit with the answer.
- Plot a table of means accurately on axes with correct scales, labels and units.
- Describe the overall trend or compare conditions shown in graphical data.
- Explain why repeated trials and a mean are used, linking this to reducing the effect of random variation in human responses.
- State a testable hypothesis linking one named independent variable to reaction time, for example that reaction time decreases after a caffeinated drink.
- Identify the independent variable, dependent variable and at least three control variables such as hand used, ruler start position and room conditions.
- Describe the ruler-drop procedure clearly, including a random release with no countdown and catching with thumb and finger.
- Explain that each condition is repeated and a mean calculated to reduce the effect of random variation in human response.
- Describe how distance data will be converted to time using t = √(2s ÷ g) and how results will be compared or displayed.
- Include a relevant safety or ethical point, such as avoiding caffeine if it causes adverse effects or obtaining consent from participants.
Examiner Tips
- 💡Structure your answer as feature → function, for example 'long axon → carries impulse a long distance in one cell'.
- 💡Use the words receptor, coordinator, effector and impulse accurately to show correct sequence.
- 💡When asked about speed, mention myelin and short synaptic gaps rather than vague words like 'fast'.
- 💡Use the sequence stimulus → receptor → coordinator → effector → response when explaining a nervous reaction.
- 💡Name a specific receptor and effector in examples, such as temperature receptors in the skin and muscles in the arm.
- 💡Link coordination to a benefit, such as avoiding injury or maintaining a stable internal environment.
- 💡Learn the pathway receptor → sensory neurone → CNS → motor neurone → effector.
- 💡When describing an effector, state whether it is a muscle contracting or a gland secreting.
- 💡Use the term electrical impulse rather than message or signal when describing transmission along neurones.
- 💡Use the exact terms stimulus, receptor, coordinator, effector and response in your answer, and apply them to the example given in the question.
- 💡When asked to complete a flow diagram, check that each arrow represents the direction of information flow from detection to response.
- 💡If the question names a specific example, such as a bright light or a hot surface, name the receptor and effector involved rather than writing generically.
- 💡Label a reflex arc diagram using the terms receptor, sensory neurone, relay neurone, motor neurone, synapse and effector.
- 💡When explaining the synapse, state that a neurotransmitter diffuses across the gap and binds to receptors on the next neurone.
- 💡Link the speed and automatic nature of reflexes to their protective function, using a named example such as withdrawing a hand from a hot surface.
- 💡When asked why a reflex is rapid, link your answer to the absence of conscious processing rather than simply saying it is fast.
- 💡Practise labelling a reflex arc diagram with receptor, sensory neurone, relay neurone, motor neurone and effector.
- 💡Use the term effector rather than only muscle or gland, because effectors include both.
- 💡If a question asks for the pathway, write the components in order and state the direction of impulse travel.
- 💡Before answering, read the axis labels and units so you quote values correctly.
- 💡When asked to compare, use comparative words such as higher, lower, faster or slower and give values for both conditions.
- 💡If asked to calculate a mean, show your working and include the unit in your answer.
- 💡Use the phrase 'the data show that...' followed by a specific value to make your interpretation clear.
- 💡When describing a graph, quote at least two numerical values from it to support the trend you state.
- 💡Check that axes are labelled with quantity and unit, and that the scale increases uniformly before plotting points.
- 💡Write the plan as a logical sequence: hypothesis, variables, method, repeats, analysis, safety.
- 💡Name specific control variables rather than saying 'keep it fair', and explain briefly why each is controlled.
- 💡State how many repeats you would take and how you would treat anomalous results before calculating a mean.
Common Mistakes
- Saying impulses travel along the myelin sheath: correct this by stating that the impulse travels along the axon and the sheath speeds it up.
- Confusing the roles of sensory and motor neurones: correct this by linking sensory to receptors and motor to effectors.
- Claiming reflexes involve no nervous coordination: correct this by stating that reflexes use a reflex arc through the spinal cord, bypassing conscious decision-making.
- Thinking the nervous system only deals with external surroundings; correction: it also coordinates internal conditions and behaviour.
- Confusing receptors with effectors; correction: receptors detect stimuli, whereas effectors produce responses.
- Believing impulses travel along the blood; correction: impulses travel along neurones as electrical signals.
- Saying the CNS is only the brain; correction: the CNS is the brain and spinal cord.
- Stating that glands contract; correction: glands secrete substances such as hormones, while muscles contract.
- Thinking impulses travel along the bloodstream; correction: impulses travel along neurones as electrical signals.
- Writing the sequence as stimulus → effector → receptor → coordinator → response. Correction: the receptor must detect the stimulus before the coordinator processes it, and the effector acts last.
- Confusing the coordinator with the effector. Correction: the coordinator is the brain or spinal cord and processes information; the effector is a muscle or gland that carries out the response.
- Stating that receptors are only in the skin. Correction: receptors are found in many organs, including the eye, ear, tongue and internal organs, wherever stimuli need to be detected.
- Saying that the relay neurone carries impulses from the receptor to the spinal cord. Correction: the sensory neurone does that; the relay neurone connects sensory and motor neurones inside the central nervous system.
- Describing the synapse as a direct electrical connection. Correction: the impulse crosses the synapse by diffusion of a neurotransmitter, which takes a small amount of time.
- Claiming that reflex actions are slow because they involve the brain. Correction: reflex actions are rapid because the impulse is coordinated by the spinal cord and does not require conscious processing by the brain.
- Error: stating that reflex actions involve the conscious part of the brain. Correction: the conscious part of the brain is not involved; the relay neurone is in the spinal cord or an unconscious region of the brain.
- Error: describing the reflex arc in the wrong order, such as motor neurone before sensory neurone. Correction: use the sequence receptor, sensory neurone, relay neurone, motor neurone, effector.
- Error: saying that a reflex action is learned or voluntary. Correction: reflex actions are automatic and involuntary from birth.
- Error: confusing the roles of sensory and motor neurones. Correction: sensory neurones carry impulses from receptors to the central nervous system; motor neurones carry impulses from the central nervous system to effectors.
- Error: reading a graph inaccurately, such as using the wrong scale interval. Correction: check the scale on each axis and count intervals carefully before quoting a value.
- Error: describing a trend without quoting data. Correction: support every description with specific values from the graph, chart or table, including units.
- Error: confusing correlation with causation. Correction: state that the data show a relationship, and only claim causation if the evidence and experimental design support it.
- Error: ignoring anomalous results when calculating a mean. Correction: identify anomalies and exclude them from the mean, or comment on their effect.
- Joining bar-chart tops with a line as if the categories were continuous; the correction is to keep separate bars for discrete conditions and reserve line graphs for continuous variables.
- Reading a graph value without its unit or misreading the scale, for example treating each small square as 1 unit when it represents 0.2 s; the correction is to check the scale before reading.
- Confusing the independent and dependent variables when plotting; the correction is to place the variable you change (e.g. caffeine dose) on the x-axis and reaction time on the y-axis.
- Changing more than one factor between conditions; the correction is to keep all variables constant except the chosen independent variable.
- Using a countdown before releasing the ruler; the correction is to release without warning so the response is genuinely reactive.
- Recording only one measurement per condition; the correction is to repeat trials and use a mean, identifying and excluding anomalies.