Source: Chapter 4, Pages 105–145, Dr. McGinty
Tags: biological psychology, nervous system, brain structures, neurons, neurotransmitters, action potential, CNS, PNS, endocrine system
Difficulty: Intermediate Prerequisites: Chapter 2 (Research Methods). You will see references to experiments and imaging studies, so understanding what those methods can tell you is helpful background.
This chapter connects psychology to biology. Everything you think, feel, and do has a biological basis in the nervous system. The chapter maps out how the nervous system is organised (central vs. peripheral), walks through the major brain structures and what they do, and then zooms in to the level of individual neurons to explain how electrical and chemical signals carry information. If you understand the hierarchy from nervous system down to synapse, and can link each brain region to its main function, you have the core of this material.
The nervous system divides into the central nervous system (brain and spinal cord) and the peripheral nervous system (everything else). Within the brain, subcortical structures handle basic functions like emotion, memory, and motivation, while the cerebral cortex handles higher-order processing. Neurons communicate electrically within themselves and chemically between each other, using neurotransmitters released at synapses.
Biological psychology
The branch of psychology that studies how biological processes (brain activity, genetics, neurochemistry) relate to behaviour and mental processes.
Central nervous system (CNS)
The brain and the spinal cord. The command centre of the body.
Peripheral nervous system (PNS)
All the nerves outside the brain and spinal cord. It carries messages between the CNS and the rest of the body.
Somatic nervous system
The division of the PNS that controls voluntary movements of skeletal muscles. Think of it as the system you use when you decide to pick up a cup.
Autonomic nervous system
The division of the PNS that controls involuntary functions like heart rate, digestion, and breathing. It operates largely without conscious effort.
Sympathetic nervous system
The "fight or flight" branch of the autonomic nervous system. It mobilises the body for action during perceived threats: increases heart rate, dilates pupils, diverts blood to muscles.
Parasympathetic nervous system
The "rest and digest" branch. It calms the body after a threat has passed: slows heart rate, promotes digestion, conserves energy. Works in opposition to the sympathetic system.
Thalamus
The brain's relay station. Nearly all sensory information (except smell) passes through the thalamus on its way to the cerebral cortex.
Hypothalamus
A small structure below the thalamus that regulates basic drives: hunger, thirst, body temperature, and sexual behaviour. It also links the nervous system to the endocrine system.
Hippocampus
Critical for forming new long-term memories. Damage to the hippocampus impairs the ability to create new memories while often leaving older memories intact.
Amygdala
A key structure in processing emotions, especially fear. Damage to the amygdala can reduce fear responses and impair the ability to recognise fear in others.
Basal ganglia
A group of subcortical structures involved in voluntary motor control, procedural learning, and habit formation. Damage is associated with movement disorders such as Parkinson's disease.
Cingulate cortex
Involved in emotion regulation, decision-making, and error detection. It sits above the corpus callosum.
Nucleus accumbens
Part of the brain's reward circuit. Involved in pleasure, motivation, and reinforcement learning. Activated by rewarding stimuli and many addictive drugs.
Cerebral cortex
The thin outer layer of the brain responsible for higher-order functions: thinking, planning, language, perception. Divided into four lobes.
Frontal lobe
The largest lobe, located at the front of the brain. Responsible for planning, decision-making, personality, voluntary movement (motor cortex), and speech production (Broca's area).
Occipital lobe
Located at the back of the brain. Primarily responsible for visual processing.
Temporal lobe
Located on the sides of the brain, near the ears. Processes auditory information, and is involved in memory and language comprehension (Wernicke's area).
Parietal lobe
Located at the top-rear of the brain. Processes somatosensory information (touch, temperature, pain) and spatial awareness.
Corpus callosum
The thick band of nerve fibres connecting the left and right cerebral hemispheres, allowing them to communicate.
Lateralisation
The idea that some functions are more strongly associated with one hemisphere than the other. Language tends to be left-lateralised, while spatial processing tends to be right-lateralised. However, both hemispheres contribute to nearly all tasks.
Neuron
A nerve cell that transmits information through electrical and chemical signals. The basic functional unit of the nervous system.
Glia (glial cells)
Support cells in the nervous system. They insulate neurons, provide nutrients, remove waste, and form myelin. They outnumber neurons and are essential for normal brain function.
Action potential
A brief electrical impulse that travels along the axon of a neuron. It is an all-or-nothing event: a neuron either fires at full strength or does not fire at all.
Myelin
A fatty insulating sheath around axons, formed by glial cells. It speeds up the transmission of action potentials.
Refractory period
A brief rest period after an action potential during which the neuron cannot fire again. It ensures that signals travel in one direction along the axon.
Synapse
The tiny gap between two neurons where chemical communication occurs.
Neurotransmitter
A chemical messenger released from the axon terminal of one neuron into the synapse, where it binds to receptors on the next neuron. Different neurotransmitters have different effects on behaviour and mental processes.
Endocrine system
A network of glands that produce hormones, which travel through the bloodstream to affect organs and behaviour. Slower than neural communication but longer-lasting. The hypothalamus and pituitary gland are central to this system.
The nervous system splits into two main divisions:
Central nervous system (CNS): Brain + spinal cord.
Peripheral nervous system (PNS): Everything else, further divided into:
Somatic nervous system: Voluntary muscle control.
Autonomic nervous system: Involuntary functions, split into:
Sympathetic: Activates the body for emergencies (fight or flight). Increases heart rate, dilates pupils, inhibits digestion.
Parasympathetic: Calms the body down afterwards (rest and digest). Slows heart rate, constricts pupils, promotes digestion.
These two branches work in opposition. When one is active, the other is relatively suppressed.
The spinal cord relays messages between the brain and the body and handles some reflexes independently (e.g., the knee-jerk reflex occurs without brain involvement).
The brainstem controls basic life-sustaining functions: breathing, heart rate, sleep-wake cycles.
The cerebellum coordinates movement, balance, and motor learning.
For each structure, know its primary function and what happens when it is damaged:
Thalamus: Sensory relay station. Damage disrupts sensory processing.
Basal ganglia: Voluntary movement and habit formation. Damage leads to movement disorders (e.g., Parkinson's disease).
Hypothalamus: Regulates drives (hunger, thirst, temperature, sex) and links to the endocrine system. Damage disrupts basic motivational behaviours.
Hippocampus: Formation of new long-term memories. Damage causes anterograde amnesia (inability to form new memories).
Cingulate cortex: Emotion regulation and error detection.
Amygdala: Processes fear and emotional significance of stimuli. Damage reduces fear responses.
Nucleus accumbens: Part of the reward pathway, involved in pleasure and motivation.
The cortex is divided into four lobes, each with specialised functions:
Frontal lobe: Planning, decision-making, personality, voluntary movement (motor cortex at the rear of the frontal lobe), speech production (Broca's area).
Occipital lobe: Visual processing.
Temporal lobe: Auditory processing, language comprehension (Wernicke's area), and memory.
Parietal lobe: Somatosensory processing (touch, pain, temperature), spatial awareness.
The claim that people are either "right-brained" (creative) or "left-brained" (logical) is a myth. Research shows that both hemispheres are active during virtually all tasks.
There is real lateralisation: language tends to be more left-hemisphere dominant, and spatial processing more right-hemisphere dominant, but both hemispheres work together.
The corpus callosum connects the two hemispheres and allows them to share information. Split-brain patients (whose corpus callosum has been severed) show that each hemisphere can function somewhat independently, but normally the two sides operate as a coordinated whole.
The endocrine system uses hormones (chemical messengers released into the bloodstream) to regulate bodily functions. It is slower than neural signalling but its effects last longer.
The hypothalamus and pituitary gland are the primary link between the nervous system and the endocrine system. The hypothalamus directs the pituitary, which in turn influences other glands throughout the body.
Key principle: Communication within a neuron is electrical. Communication between neurons is chemical.
Neuron structure:
Dendrites: Receive signals from other neurons.
Cell body (soma): Contains the nucleus, integrates incoming signals.
Axon: Carries the electrical signal (action potential) away from the cell body toward the axon terminal.
Axon terminal: Releases neurotransmitters into the synapse.
Myelin sheath: Insulates the axon, speeding up signal transmission.
Glial cells support neurons by providing nutrients, insulating axons (forming myelin), cleaning up debris, and guiding neural development. Without glia, neurons cannot function properly.
Five things to remember:
Action potentials travel toward the end of the axon (from cell body to axon terminal).
They are all or nothing: a neuron either fires at full strength or does not fire. There is no partial firing.
All action potentials are the same strength. A stronger stimulus does not produce a bigger action potential; instead, it causes the neuron to fire more frequently.
The speed of an action potential depends on the presence of myelin. Myelinated axons transmit signals much faster.
After each action potential, there is a refractory period, a brief rest during which the neuron cannot fire again.
The action potential is triggered when incoming signals push the neuron's electrical charge past a threshold. Once threshold is reached, the neuron fires.
When an action potential reaches the axon terminal, it triggers the release of neurotransmitters into the synaptic gap.
Neurotransmitters cross the synapse and bind to receptors on the receiving neuron.
This can either excite the next neuron (making it more likely to fire) or inhibit it (making it less likely to fire).
After binding, neurotransmitters are either broken down by enzymes or taken back up into the sending neuron (reuptake).
Know the major neurotransmitters and their general roles. The review sheet flags this as testable content, and specific neurotransmitters come up again in Chapter 6 (psychoactive drugs).
Students often think people are either "right-brained" or "left-brained." Research does not support this. Both hemispheres are active in virtually all cognitive tasks.
Students sometimes confuse the sympathetic and parasympathetic systems. A useful mnemonic: sympathetic = stress (fight or flight); parasympathetic = peace (rest and digest).
Students often assume that a stronger stimulus produces a stronger action potential. It does not. Action potentials are all-or-nothing. A stronger stimulus simply causes more frequent firing.
Students sometimes think neurotransmitters only excite neurons. They can also inhibit them, making the next neuron less likely to fire.
⚠️ Be able to trace the path of information through the nervous system: stimulus > PNS > CNS > processing > response.
⚠️ Know the function of each subcortical structure and what deficits result from damage to it.
⚠️ Understand the all-or-nothing principle of the action potential and the role of myelin.
⚠️ Be ready to explain the difference between electrical signalling (within a neuron) and chemical signalling (between neurons).
⚠️ Distinguish between the four lobes of the cerebral cortex and their primary functions.
⚠️ The sympathetic vs. parasympathetic distinction is a frequent exam question.
True or False: The hippocampus is primarily involved in processing fear. False. The hippocampus is primarily involved in forming new memories. The amygdala processes fear.
Fill in the blank: Communication within a neuron is ________, while communication between neurons is ________. Electrical; chemical.
True or False: A stronger stimulus produces a larger action potential. False. Action potentials are all-or-nothing and always the same strength.
Fill in the blank: The ________ connects the left and right hemispheres of the brain. Corpus callosum.
True or False: The parasympathetic nervous system prepares the body for fight or flight. False. That is the sympathetic nervous system.
Q: A patient suffers damage to the hippocampus. What is the most likely cognitive deficit?
A: The patient would likely develop anterograde amnesia, an inability to form new long-term memories, while older memories formed before the damage might remain relatively intact.
Q: Explain why myelin is important for neural communication.
A: Myelin insulates the axon, which allows the action potential to travel much faster by jumping between gaps in the myelin sheath (nodes of Ranvier). Without myelin, signals slow down significantly, as seen in conditions like multiple sclerosis.
Q: What is the difference between the somatic and autonomic nervous systems?
A: The somatic nervous system controls voluntary movements (e.g., reaching for an object). The autonomic nervous system controls involuntary functions (e.g., heart rate, digestion).
Q: How do the sympathetic and parasympathetic nervous systems work together?
A: They operate in opposition. The sympathetic system activates the body during stress (increasing heart rate, diverting blood to muscles). The parasympathetic system restores the body to a calm state afterwards (slowing heart rate, promoting digestion). This balance allows the body to respond to threats and then recover.
Q: A neuron receives a signal that pushes it just past its threshold. What happens?
A: The neuron fires an action potential at full strength. After firing, a refractory period occurs before it can fire again. The action potential travels down the axon to the axon terminal, where neurotransmitters are released into the synapse.
The neurotransmitter systems introduced here are directly relevant to Chapter 6 (Consciousness), where psychoactive drugs are discussed in terms of which neurotransmitters they affect. The brain structures covered here, particularly the thalamus and the visual cortex, come up again in Chapter 5 (Perception) when you trace how visual information travels from the eye to the brain.
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