Brain and Neuropsychology — AQA GCSE Psychology Revision Notes
What you'll learn
- How the nervous system is divided, and what each part does
- The three types of neuron and how a signal crosses from one to the next
- The reflex arc, and why bypassing the brain is an advantage
- The main structures of the brain and the functions localised in each
- Broca's and Wernicke's areas, and how aphasia patterns reveal what each does
- What scanning techniques actually measure, and what they can and cannot prove
- How to evaluate localisation of function given evidence that the brain can reorganise
Key terms and definitions
Central nervous system (CNS) — the brain and spinal cord.
Peripheral nervous system — the network of nerves carrying signals between the CNS and the rest of the body.
Sensory neuron — carries impulses from receptors towards the CNS.
Relay neuron — connects sensory and motor neurons, found mainly within the CNS.
Motor neuron — carries impulses from the CNS to muscles and glands.
Synapse — the gap between two neurons, across which signals pass.
Neurotransmitter — a chemical released into the synapse to carry a signal to the next neuron.
Myelin sheath — a fatty insulating layer around an axon that speeds up transmission.
Reflex arc — the pathway of a fast, automatic response that does not require conscious thought.
Cerebral cortex — the outer layer of the brain, divided into four lobes.
Cerebellum — the structure that coordinates and fine-tunes movement and balance.
Medulla — the structure controlling vital automatic functions such as breathing and heart rate.
Localisation of function — the idea that specific brain areas are responsible for specific functions.
Contralateral control — each hemisphere controlling the opposite side of the body.
Aphasia — a language impairment resulting from brain damage.
fMRI — a scanning technique measuring changes in blood flow and oxygen use to show brain activity.
Core concepts
Divisions of the nervous system
The nervous system splits into the central nervous system — the brain and spinal cord — and the peripheral nervous system, the nerves connecting the CNS to the rest of the body. The CNS processes and decides; the peripheral system carries information in and instructions out.
Neurons and synaptic transmission
Three types of neuron do the work. Sensory neurons carry impulses from receptors towards the CNS. Motor neurons carry impulses from the CNS out to muscles. Relay neurons connect the two and lie mainly within the CNS.
Transmission happens in two different ways, and the distinction is frequently examined. Within a neuron, the signal travels as an electrical impulse along the axon. Between neurons it cannot, because there is a physical gap — the synapse. The signal is carried across chemically: the first neuron releases neurotransmitters into the gap, and receptors on the next neuron detect them and generate a new electrical impulse.
The myelin sheath insulates the axon in sections, so the impulse jumps between the gaps rather than travelling the full length continuously. This is why myelinated neurons conduct so much faster, and why losing myelin slows conduction and disrupts function.
The reflex arc
In a reflex such as pulling a hand from a hot surface, the route is: receptor → sensory neuron → relay neuron in the spinal cord → motor neuron → muscle. The brain is informed, but the response does not wait for it.
Bypassing conscious processing removes the delay, so the withdrawal happens before damage accumulates. The cost is that the response is fixed and cannot be adjusted to circumstances — acceptable where any delay is more dangerous than an occasionally inappropriate reaction.
Structures of the brain
The cerebral cortex is the outer layer, divided into four lobes:
- Frontal lobe — contains the motor area, which initiates voluntary movement, and Broca's area
- Parietal lobe — contains the somatosensory area, which processes touch, pressure and pain
- Temporal lobe — contains the auditory area and Wernicke's area
- Occipital lobe — contains the visual area, at the back of the brain
The cerebellum coordinates and fine-tunes movement and balance. Crucially it does not initiate movement, so damage to it produces clumsy, poorly balanced action rather than paralysis — the muscles still work, but the refinement is gone.
The medulla controls vital automatic functions including breathing and heart rate. Damage here is life-threatening because no other structure can take these over.
Two organising principles are worth knowing. Contralateral control means the motor pathways cross over, so damage to the left motor area affects movement on the right side of the body. And the amount of cortex given to a body part reflects how much precision or sensitivity it requires rather than its physical size — the hands and lips command large territories in both the motor and somatosensory areas, the trunk very little. This is why fine manipulation and speech are possible, and why losing a small area of cortex can remove a disproportionately important ability.
Language areas and aphasia
Broca's area, in the frontal lobe of usually the left hemisphere, is associated with the production of speech. Damage produces a patient who understands what is said but produces speech only slowly and with great effort.
Wernicke's area, in the temporal lobe of usually the left hemisphere, is associated with the understanding of language. Damage produces a patient who speaks fluently but whose sentences carry little meaning, and who struggles to understand others.
These two patterns are powerful evidence. Fluent speech without meaning, and effortful speech with intact comprehension, show that producing and understanding language depend on separable systems rather than one undivided language faculty. The pattern of what is lost against what is spared is what localises the damage.
Localisation of function
Localisation of function is the claim that specific areas are responsible for specific functions. Evidence comes from two main sources.
Brain damage cases. If a specific ability is lost when a particular area is damaged while other abilities remain, that area was apparently necessary for the lost ability. This is one of the few sources of causal evidence available in humans.
Scanning studies. These show consistent activation of particular areas during particular tasks, in healthy living brains.
Both sources have limits. Damage is rarely confined to one structure, so the lost ability may depend on an adjacent region or on a connection rather than the area identified. Each patient's injury is unique, so findings may not generalise. And the brain may already have begun reorganising by the time it is assessed, meaning what remains is not simply the healthy brain minus one part.
Against strict localisation, many functions depend on networks spanning several areas, and the brain can sometimes reorganise so another region takes over a lost function. That capacity matters practically — it means rehabilitation can restore ability rather than merely compensating for its loss — but it also shows the original mapping was a tendency rather than a fixed requirement.
Scanning techniques
fMRI measures changes in blood flow and oxygen use, which indicate where activity is higher during a task. Activity is therefore inferred from blood supply rather than measured directly, with a delay of seconds.
Compared with a CT scan, which shows structure at a single moment, fMRI shows activity while a person performs a task, so function can be linked to location. It also avoids exposure to radiation.
The critical limitation: an area lighting up during a task shows that it is active, not that it is necessary. Scans establish correlation between activity and task, and the striking images can lend a claim more authority than the underlying data supports.
Why this matters for psychology
If particular thoughts, memories and emotions depend on identifiable brain processes, explanations of behaviour can be grounded in physical mechanisms rather than description alone. That is the basis of cognitive neuroscience.
The qualification worth making in evaluation is that describing which regions are active does not explain why a person holds a particular belief, or how social context shapes their choices. The biological account is necessary without being sufficient.
Worked examples
Example 1: The reflex arc
Describe the pathway of a reflex response when a person touches a hot surface. (4 marks)
Receptors in the skin detect the heat and generate an impulse (1). A sensory neuron carries the impulse to the spinal cord (1), where a relay neuron passes it directly to a motor neuron (1). The motor neuron carries the impulse to the muscle, which contracts and withdraws the hand (1).
Marks are lost by omitting the relay neuron or by routing the signal through the brain.
Example 2: Synaptic transmission
Explain how a signal passes from one neuron to the next. (3 marks)
There is a physical gap between the neurons called the synapse, so the electrical impulse cannot travel directly across (1). The first neuron releases neurotransmitters into the synapse (1), which are detected by receptors on the next neuron and generate a new impulse in it (1).
Example 3: Interpreting an aphasia case
A patient speaks fluently but their sentences make little sense, and they cannot follow instructions. Identify the likely damaged area and justify your answer. (3 marks)
The damage is most likely to Wernicke's area (1). Speech production remains fluent, which indicates Broca's area is intact (1), while the loss of meaning and of comprehension points to the area responsible for understanding language (1).
The justification marks come from ruling out the alternative — say what is spared, not only what is lost.
Example 4: Evaluating a scanning study
A study finds an area is more active when participants recall memories. Explain one limitation of concluding that this area is responsible for memory. (2 marks)
The study shows only that the area is active during the task, which is a correlation (1). It does not establish that the area is necessary for memory, since the activity could reflect a related process such as attention rather than memory itself (1).
Common mistakes and how to avoid them
Saying transmission across the synapse is electrical. Within a neuron it is electrical; across the synapse it is chemical. Questions test exactly this.
Leaving the relay neuron out of the reflex arc. Sensory → relay → motor. All three.
Confusing the cerebellum with the motor area. The motor area initiates movement; the cerebellum coordinates it. This is why cerebellar damage causes clumsiness rather than paralysis.
Swapping Broca and Wernicke. Broca is production — effortful speech, comprehension intact. Wernicke is understanding — fluent speech, meaning lost.
Saying fMRI measures neuron firing. It measures blood flow and oxygen use as a proxy, with a delay.
Treating a scan as proof of cause. Activation shows involvement, not necessity. This is the single most common evaluation point and the easiest mark to pick up.
Claiming brain damage cases are conclusive. They are valuable and irreplaceable but each injury is unique and rarely confined to one structure.
Forgetting contralateral control. Left hemisphere damage affects the right side of the body.
Exam technique for Brain and Neuropsychology
Learn the pathways as sequences. The reflex arc and synaptic transmission are both step-by-step, and marks are awarded per correct step. Rehearse them in order.
Use the structure's function, not its name. "The medulla was damaged" earns little; "the medulla controls breathing and heart rate, so damage is life-threatening" earns the mark.
For aphasia questions, state what is spared. The diagnosis comes from the contrast between the lost and retained abilities.
Give the limitation of every method you mention. For fMRI: correlation not causation, blood flow as a proxy, delay. For case studies: uniqueness and imprecise damage.
Watch the ethics angle on patient research. Patients with brain damage may have impaired capacity to consent, repeated testing can be distressing and offers them no personal benefit, and detailed case histories risk identifying them.
In extended answers, take a position on localisation. The defensible line is that specialisation is real and well evidenced, but functions often depend on networks and the brain can partly reorganise — so localisation describes a strong tendency rather than a rigid map.
Quick revision summary
- CNS = brain + spinal cord; peripheral nervous system carries signals to and from it
- Sensory neurons in, motor neurons out, relay neurons connect them within the CNS
- Within a neuron the signal is electrical; across the synapse it is chemical, via neurotransmitters
- Myelin sheath insulates the axon so the impulse jumps between gaps, speeding transmission
- Reflex arc: receptor → sensory → relay → motor → muscle, bypassing the brain for speed
- Lobes: frontal (motor, Broca), parietal (somatosensory), temporal (auditory, Wernicke), occipital (visual)
- Cerebellum coordinates movement — damage causes clumsiness, not paralysis
- Medulla controls breathing and heart rate — damage is life-threatening
- Contralateral control: each hemisphere controls the opposite side of the body
- Cortical space reflects precision required, not body-part size
- Broca = speech production; Wernicke = language understanding; the two aphasias show separable systems
- fMRI measures blood flow and oxygen as a proxy for activity, and shows correlation not necessity
- Localisation is well supported but functions often span networks, and the brain can reorganise
- Reorganisation makes rehabilitation possible and complicates strict localisation at the same time