Notes · PsychologyUK · A-Levels

Biopsychology

Biopsychology studies the biological basis of behaviour. This chapter covers the divisions of the nervous system and the neuron, the process of synaptic transmission, the endocrine system and the fight-or-flight response, the localisation and lateralisation of brain function, plasticity and recovery after trauma, the ways of studying the brain, and the biological rhythms that govern the sleep-wake cycle.

6 sections~20 min reading time3 competenciesLevel Foundation 1 · Standard 2 · Advanced 3

T·0666 / 17

Exam profile

AO1 · Describe the nervous and endocrine systems, synaptic transmission, localisation, plasticity, scanning methods and biological rhythmsAO2 · Apply the biology of behaviour to novel scenarios and to research designsAO3 · Evaluate localisation, plasticity, the scanning techniques and the pacemaker/zeitgeber evidence

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basic level

AS-Level covers the divisions of the nervous system, neurons, synaptic transmission, the endocrine system and the fight-or-flight response.

higher level

The full A-Level adds localisation and lateralisation, plasticity and functional recovery, ways of studying the brain, and biological rhythms.

Depth

Text

Contents · 6 sections

Biopsychology

The divisions of the nervous system and types of neuron#

FoundationAQA 7182 3.2.2DfE GCE Psychology - the nervous system

The divisions of the nervous system

Fig. 1The nervous system divides into the CNS and PNS; the autonomic branch of the PNS splits into the sympathetic and parasympathetic systems.

The nervous system is the body's electrochemical communication network, and it has two main divisions. The central nervous system (CNS) consists of the brain (the centre of conscious awareness and control) and the spinal cord (which relays messages to and from the brain and controls reflexes). The peripheral nervous system (PNS) carries messages between the CNS and the rest of the body, and is itself divided into the somatic nervous system (which controls voluntary movement of skeletal muscles and carries sensory information to the CNS) and the autonomic nervous system (which controls involuntary functions such as heart rate and digestion).

The autonomic nervous system has two opposing branches. The sympathetic branch is the 'arousing' system that prepares the body for action (increasing heart rate, dilating pupils), and is central to the fight-or-flight response. The parasympathetic branch is the 'calming' system that returns the body to rest (slowing the heart, promoting digestion), sometimes called 'rest and digest'. The two work antagonistically to keep the body in balance.

Information travels through the nervous system along neurons - specialised cells that transmit electrical signals. There are three types. The sensory neuron carries messages from the sensory receptors (in the skin, eyes, etc.) to the CNS; it has long dendrites and a short axon. The relay neuron connects sensory and motor neurons (and other neurons) within the CNS; it has short dendrites and a short axon. The motor neuron carries messages from the CNS to effectors (muscles and glands); it has short dendrites and a long axon.

A typical neuron has a cell body (soma) containing the nucleus, dendrites that receive signals from other neurons, and an axon that carries the electrical impulse away from the cell body. Many axons are insulated by a fatty myelin sheath, broken at intervals by the nodes of Ranvier, which speeds up transmission by allowing the impulse to 'jump' between nodes. When a neuron is activated, the inside briefly becomes positively charged, producing an electrical impulse called the action potential that travels down the axon to the axon terminals.

A motor neuron

Fig. 2A motor neuron: short dendrites receive signals; the long, myelinated axon carries the impulse to the axon terminals.

Worked example

Tracing a reflex through the nervous system

Describe the path of the nervous impulse in a simple reflex, from touching a hot surface to withdrawing the hand, naming the neurons involved.

Detection
Sensory receptors in the skin detect heat and a sensory neuron carries the impulse to the CNS (spinal cord).
Relay
Within the spinal cord a relay neuron passes the impulse straight to a motor neuron (a reflex arc), without waiting for the brain.
Response
The motor neuron carries the impulse to the effector (an arm muscle), which contracts to withdraw the hand.

Result: Sensory neuron -> relay neuron -> motor neuron -> effector: a rapid reflex arc through the spinal cord.

Typical mistakes

Placing the sympathetic/parasympathetic split under the somatic system - it belongs to the autonomic system.
Confusing sensory (receptors to CNS) and motor (CNS to effectors) neurons.

Active revision

Name the division of the nervous system responsible for each: reading these words; your heartbeat; jumping back from a hot pan.

Active recall

Recall the key points — then reveal.

Sources: GCE AS and A level subject content for psychology (Department for Education) · AQA A-level Psychology 7182 specification (AQA)

Synaptic transmission#

AdvancedAQA 7182 3.2.2DfE GCE Psychology - synaptic transmission

Synaptic transmission

Fig. 3The action potential triggers vesicles to release neurotransmitter, which diffuses across the cleft and binds to postsynaptic receptors.

Neurons are not physically joined; there is a tiny gap between them called the synapse (or synaptic cleft), and signals must cross it chemically. Within a neuron the signal is electrical (the action potential), but between neurons it is chemical - carried by molecules called neurotransmitters. Understanding this electrical-to-chemical-to-electrical conversion is the core of the topic.

The process of synaptic transmission runs as follows. When the action potential reaches the end of the presynaptic neuron (the axon terminal), it triggers synaptic vesicles to release their neurotransmitter into the synaptic cleft. The neurotransmitter diffuses across the cleft and binds to specific receptors on the membrane of the postsynaptic neuron - each neurotransmitter has a specific molecular shape that fits particular receptors, like a lock and key. Once it has had its effect, the neurotransmitter is removed from the cleft by reuptake (reabsorption into the presynaptic neuron) or by enzymes, so the signal does not continue indefinitely.

Neurotransmitters have either an excitatory or an inhibitory effect on the postsynaptic neuron. An excitatory neurotransmitter (such as noradrenaline) makes the postsynaptic neuron more likely to fire, by making its charge more positive; an inhibitory neurotransmitter (such as GABA) makes it less likely to fire, by making its charge more negative. Some neurotransmitters (such as dopamine) can do either depending on the receptor. This distinction matters because many drugs and disorders act by shifting the balance of excitation and inhibition.

A postsynaptic neuron receives many signals at once, and whether it fires depends on summation - the adding-up of these inputs. The excitatory and inhibitory signals are summed: if the net effect makes the inside of the neuron sufficiently positive to reach the threshold, an action potential is triggered and the neuron 'fires'; if it does not reach threshold, the neuron does not fire (the all-or-nothing principle). This is why the nervous system can perform complex processing - each neuron acts as a tiny decision-maker integrating thousands of inputs. Because transmission across the synapse is one-way (vesicles are only on the presynaptic side and receptors only on the postsynaptic side), information flows in a single direction.

Worked example

Reasoning about summation

A postsynaptic neuron simultaneously receives three strong excitatory signals and one weak inhibitory signal. Explain whether it is likely to fire.

Identify the inputs
Three excitatory inputs push the neuron's charge towards positive; one weak inhibitory input pushes it slightly negative.
Apply summation
The net effect is the sum of all inputs; here the excitatory inputs strongly outweigh the single weak inhibitory one.
Compare to the threshold
Because the summed excitation is likely to raise the charge past the threshold, an action potential is triggered and the neuron fires (all-or-nothing).

Result: The net excitation exceeds the threshold, so the neuron fires.

Typical mistakes

Saying the signal is electrical across the synapse - it is chemical across the synapse and electrical within the neuron.
Confusing excitation (more likely to fire) with inhibition (less likely to fire).

Active revision

Explain how excitatory and inhibitory signals determine whether a postsynaptic neuron fires.

Active recall

Recall the key points — then reveal.

Sources: GCE AS and A level subject content for psychology (Department for Education) · AQA A-level Psychology 7182 specification (AQA)

The endocrine system and the fight-or-flight response#

StandardAQA 7182 3.2.2DfE GCE Psychology - the endocrine system and fight-or-flight

The sympathomedullary (fight-or-flight) pathway

Fig. 4A perceived threat triggers the SAM pathway: hypothalamus, sympathetic nervous system, adrenal medulla and adrenaline, producing the fight-or-flight changes.

The endocrine system is the body's slower chemical communication network. It works alongside the nervous system, using glands that secrete hormones - chemical messengers carried in the bloodstream - which act on target organs with receptors for them. Hormones act more slowly than nerve impulses but their effects are widespread and longer-lasting. The pituitary gland, in the brain, is often called the 'master gland' because it controls the release of hormones from many of the other glands.

Key glands and hormones include the pituitary (controls other glands), the adrenal glands on top of the kidneys (release adrenaline and cortisol), the thyroid (releases thyroxine, controlling metabolism), the testes (testosterone) and the ovaries (oestrogen). The endocrine and nervous systems often work together: the hypothalamus in the brain links the two by controlling the pituitary.

The fight-or-flight response is an acute reaction to a perceived threat that prepares the body for action. When the hypothalamus detects a stressor it activates the sympathetic branch of the autonomic nervous system, which stimulates the adrenal medulla (the inner part of the adrenal gland) to release adrenaline into the bloodstream - this is the sympathomedullary (SAM) pathway. Adrenaline produces rapid physiological changes: increased heart rate and blood pressure (delivering oxygen and glucose to the muscles), faster breathing, dilated pupils and the diversion of blood away from digestion. These changes ready the body either to confront the threat (fight) or to escape it (flight).

Once the threat passes, the parasympathetic branch takes over and returns the body to its resting state (the 'rest and digest' response), lowering heart rate and restoring digestion. The response is evaluated as adaptive - it evolved to help our ancestors survive immediate physical dangers - but the account is criticised for being based largely on male physiology: Taylor et al. proposed that females may show a 'tend and befriend' response (protecting offspring and forming alliances) rather than fight or flight, so the fight-or-flight model may be an example of beta bias that ignores gender differences. It is also argued that repeated activation of the stress response in modern life, where threats are chronic rather than acute physical dangers, can damage health.

Worked example

Explaining a fight-or-flight symptom

A person about to give a speech notices their heart pounding and dry mouth. Explain these using the fight-or-flight response.

Identify the trigger
The perceived threat (public speaking) is detected by the hypothalamus, which activates the sympathetic nervous system and adrenal medulla.
Explain the pounding heart
Adrenaline increases heart rate and blood pressure to deliver more oxygen and glucose to the muscles, preparing for action.
Explain the dry mouth
Blood and resources are diverted away from non-essential functions such as digestion and saliva production, causing the dry mouth.

Result: Adrenaline's actions - raising heart rate and suppressing digestion - explain both the pounding heart and the dry mouth.

Typical mistakes

Confusing the fast nervous system with the slower endocrine (hormonal) system.
Saying adrenaline comes from the pituitary - it comes from the adrenal medulla.

Active revision

Describe the bodily changes produced by adrenaline in the fight-or-flight response and explain how each helps the body respond to a threat.

Active recall

Recall the key points — then reveal.

Sources: GCE AS and A level subject content for psychology (Department for Education) · AQA A-level Psychology 7182 specification (AQA)

Localisation and lateralisation of brain function#

AdvancedAQA 7182 3.2.2DfE GCE Psychology - localisation of function

Localisation of function in the cortex

Fig. 5Named cortical centres: motor and somatosensory areas, the visual (occipital) and auditory (temporal) centres, and the two language areas.

Localisation of function is the idea that specific areas of the brain are responsible for specific behaviours and processes, rather than the whole cortex being involved in everything (the opposite view is holistic theory). The cortex is divided into four lobes, and several centres are named on the specification. The motor area (frontal lobe) controls voluntary movement; the somatosensory area (parietal lobe) processes sensory information such as touch; the visual centre (occipital lobe) processes vision; and the auditory centre (temporal lobe) processes sound.

Two language centres are especially important. Broca's area, in the left frontal lobe, is responsible for speech production; damage causes Broca's aphasia, in which speech is slow, laboured and lacking in fluency. Wernicke's area, in the left temporal lobe, is responsible for language comprehension; damage causes Wernicke's aphasia, in which speech is fluent but meaningless. These were identified from patients with brain damage (Broca's patient 'Tan' could understand language but could say almost nothing), providing early evidence for localisation.

Hemispheric lateralisation is the idea that the two halves of the brain are functionally different, with some processes dominant in one hemisphere. Language is lateralised to the left hemisphere in most people, while the right hemisphere is more involved in tasks such as spatial processing and recognising faces. The two hemispheres normally communicate through the corpus callosum, a thick band of fibres connecting them.

The key evidence for lateralisation comes from Sperry's split-brain research on patients whose corpus callosum had been surgically cut (to treat severe epilepsy), so the two hemispheres could no longer communicate. By presenting information to only one visual field (and therefore one hemisphere) at a time, Sperry showed, for example, that an object shown to the right hemisphere could not be named (because language is in the left hemisphere) but could be selected by touch with the left hand. Localisation and lateralisation are evaluated as well supported by brain-scan and case-study evidence, but the picture is more complex than a simple 'one area, one function': plasticity means functions can shift after damage, individual differences exist, and split-brain patients are a small, unusual sample.

Worked example

Interpreting a split-brain result

In a split-brain study an image of a key is flashed to a patient's left visual field and they are asked to name it. Predict the outcome and explain it.

Trace the pathway
The left visual field projects to the right hemisphere; with a severed corpus callosum this information cannot cross to the left hemisphere.
Apply lateralisation
Language (naming) is a left-hemisphere function, but the image is only available to the right hemisphere.
Predict
The patient cannot name the key verbally, but could select it by touch with the left hand (controlled by the right hemisphere) - showing the right hemisphere 'knew' the object without being able to name it.

Result: The patient cannot name the key (right hemisphere lacks language) but can pick it out with the left hand - evidence for lateralisation.

Typical mistakes

Swapping Broca's (production, frontal) and Wernicke's (comprehension, temporal) areas and their aphasias.
Treating localisation as absolute - plasticity and individual differences complicate the 'one area, one function' view.

Active revision

A patient can understand speech perfectly but produces only slow, broken sentences. Identify the likely area of damage and the type of aphasia.

Active recall

Recall the key points — then reveal.

Sources: GCE AS and A level subject content for psychology (Department for Education) · AQA A-level Psychology 7182 specification (AQA)

Plasticity, functional recovery and ways of studying the brain#

AdvancedAQA 7182 3.2.2DfE GCE Psychology - plasticity and ways of studying the brain

Ways of studying the brain

Fig. 6The methods trade off spatial against temporal resolution; the choice depends on the research question.

Plasticity is the brain's ability to change and adapt its structure and function throughout life as a result of experience and learning. Although synaptic connections are most numerous in infancy, the adult brain continues to form new connections and prune unused ones. A striking demonstration is Maguire et al.'s study of London taxi drivers, who had a larger posterior hippocampus (a region associated with spatial navigation) than controls, and more so the longer they had been driving - showing that the demands of learning 'the Knowledge' of London's streets had physically reshaped the brain.

Functional recovery is a form of plasticity following trauma such as a stroke: after damage, the brain can transfer functions previously performed by the damaged areas to undamaged ones. This happens through processes such as axonal sprouting (new nerve endings grow to connect with undamaged neurons), the recruitment of homologous (equivalent) areas on the opposite hemisphere, and the reformation of blood vessels. Recovery is often rapid at first and then slows, and can be supported by rehabilitation. Plasticity and recovery are evaluated as having valuable real-world application (neurorehabilitation) and strong support, though recovery can decline with age and the reorganisation is not always beneficial (it can produce maladaptive changes, such as phantom-limb pain).

Because the brain cannot be observed directly in a living person, psychologists use several ways of studying it, each with strengths and limitations. Functional magnetic resonance imaging (fMRI) measures blood flow in the brain while a person performs a task, showing which areas are active with good spatial detail but poor temporal resolution (a delay of a few seconds). The electroencephalogram (EEG) records the brain's overall electrical activity through scalp electrodes, with excellent temporal resolution but poor spatial resolution. Event-related potentials (ERPs) are derived from EEG by averaging the responses to many presentations of a stimulus, isolating the brain's response to that specific event.

Post-mortem examination studies the brain after death, often relating observed damage to behaviour the person showed while alive (as in the historical study of Broca's and Wernicke's patients). It allows detailed examination of deep structures, but cannot establish cause and effect (damage may be unrelated to the behaviour, or have occurred after it) and raises consent issues. Choosing between these methods is a common exam task: the right method depends on whether the researcher needs precise timing (EEG/ERP) or precise location (fMRI), and whether the study is of a living or deceased brain.

Worked example

Selecting a brain-scanning method

A team wants to pinpoint precisely which small region is active when a person recognises a face. Which method should they use and why?

Identify the requirement
The question is about location (which region), so high spatial resolution matters more than timing.
Match to a method
fMRI provides good spatial resolution by measuring blood flow, so it can localise the active region.
Note the trade-off
The cost is fMRI's poor temporal resolution (a few-second lag), which is acceptable here because timing is not the focus.

Result: fMRI is the appropriate choice because it offers the spatial detail needed to localise the active region.

Typical mistakes

Confusing spatial resolution (where) with temporal resolution (when) - fMRI is strong on where, EEG on when.
Treating post-mortem findings as proving that damage caused a behaviour - it cannot establish cause and effect.

Active revision

A researcher wants to know exactly when in the first second the brain reacts to a sound. Recommend a method and justify your choice.

Active recall

Recall the key points — then reveal.

Sources: GCE AS and A level subject content for psychology (Department for Education) · AQA A-level Psychology 7182 specification (AQA)

Biological rhythms#

StandardAQA 7182 3.2.2DfE GCE Psychology - biological rhythms

The circadian sleep-wake rhythm

Fig. 7The circadian rhythm cycles roughly every 24 hours, with alertness peaking in the afternoon and dipping in the early hours (illustrative shape).

Biological rhythms are cyclical changes in the body governed by internal biological clocks and external cues, and the specification names three types by their length. A circadian rhythm lasts about 24 hours (the sleep-wake cycle and body temperature). An infradian rhythm lasts longer than 24 hours (the roughly 28-day menstrual cycle, or seasonal affective disorder as an annual rhythm). An ultradian rhythm lasts less than 24 hours, occurring more than once a day (the roughly 90-minute cycle of stages of sleep through the night).

Rhythms are controlled by an interaction of internal and external factors. Endogenous pacemakers are internal biological clocks: the master clock is the suprachiasmatic nucleus (SCN) in the hypothalamus, which regulates the sleep-wake cycle and controls the pineal gland's release of the hormone melatonin, which promotes sleep. Exogenous zeitgebers ('time-givers') are external cues that reset the internal clock to the outside world, the most important being light, along with social cues such as mealtimes.

The sleep-wake cycle illustrates the interaction. Left to run freely without external cues, the human clock settles to a rhythm of roughly (but not exactly) 24 hours, as Siffre found when he spent long periods in a cave with no natural light - his 'day' drifted to around 25 hours. This shows the rhythm is largely endogenous but must normally be reset each day by zeitgebers such as daylight to stay locked to the 24-hour environment. Jet lag and shift work, which disrupt the match between the internal clock and external time, cause the tiredness and impaired performance that follow.

The evidence is evaluated carefully. Free-running studies such as Siffre's demonstrate the endogenous clock but are single-participant case studies, so individual differences (people's natural cycles vary) limit generalisation, and even 'isolation' studies often let in artificial light, a confounding zeitgeber. Research also has practical value - understanding circadian rhythms informs the timing of medication (chronotherapeutics) and the management of shift work - but ethical and methodological issues (small samples, disrupting participants' sleep) mean conclusions are drawn with caution.

Worked example

Explaining a free-running rhythm

Siffre's sleep-wake cycle settled to about 25 hours when he lived underground without natural light. Explain what this shows about the control of circadian rhythms.

Note the persistence of the rhythm
A rhythm continued even without external cues, showing it is generated internally by an endogenous pacemaker (the SCN).
Note the drift
The cycle lengthened to about 25 rather than exactly 24 hours, showing the internal clock is not perfectly accurate.
Draw the conclusion
Normally exogenous zeitgebers such as daylight reset the clock each day to keep it locked to the 24-hour environment; without them, it free-runs slightly slow.

Result: The rhythm is endogenous but imprecise, so zeitgebers are needed to entrain it to the 24-hour day.

Typical mistakes

Mixing up infradian (longer than a day) and ultradian (shorter than a day) rhythms.
Saying the free-running clock is exactly 24 hours - it drifts to about 25 hours without zeitgebers.

Active revision

Explain why a long-haul flight across several time zones causes jet lag, using endogenous pacemakers and exogenous zeitgebers.

Active recall

Recall the key points — then reveal.

Sources: GCE AS and A level subject content for psychology (Department for Education) · AQA A-level Psychology 7182 specification (AQA)

References & sources

Sources

Department for Education

GCE AS and A level subject content for psychology

AQA

AQA A-level Psychology 7182 specification

Biopsychology

6 sections~20 min reading time3 competenciesLevel Foundation 1 · Standard 2 · Advanced 3

Biopsychology

Key points

Tracing a reflex through the nervous system

Key points

Reasoning about summation

Key points

Explaining a fight-or-flight symptom

Key points

Interpreting a split-brain result

Key points

Selecting a brain-scanning method

Key points

Explaining a free-running rhythm

Sources

Biopsychology

Key points

Tracing a reflex through the nervous system

Key points

Reasoning about summation

Key points

Explaining a fight-or-flight symptom

Key points

Interpreting a split-brain result

Key points

Selecting a brain-scanning method

Key points

Explaining a free-running rhythm

Sources