The brain is the coordination centre of the nervous system, containing around 100 billion neurones. It has three main functional regions — the cerebral cortex, cerebellum, and medulla — each controlling different bodily functions, from conscious thought to heartbeat regulation.
What is the structure of the human nervous system?
The nervous system has two main divisions:
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Central nervous system (CNS) — the brain and spinal cord. This is the coordination centre: it receives signals (impulses) from sensory receptors, processes them, and sends out appropriate responses.
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Peripheral nervous system (PNS) — all the nerves running between the CNS and the rest of the body. These include:
- Sensory neurones — carry impulses from receptors (eyes, ears, skin, etc.) to the CNS
- Motor neurones — carry impulses from the CNS to effectors (muscles and glands)
At GCSE the key circuit is: stimulus → receptor → sensory neurone → CNS → motor neurone → effector → response. For very fast responses (reflexes), the spinal cord acts as the relay point rather than the brain — this is covered in the KS3 reflexes topic. At GCSE, the focus shifts to the brain itself.
What are the three main regions of the brain?
The brain is a profoundly complex organ, but GCSE requires you to know the functions of three key regions:
| Brain region | Location | Functions |
|---|---|---|
| Cerebral cortex | Large outer layer covering most of the brain | Conscious thought, language, memory, personality, intelligence, sensory perception, voluntary movement |
| Cerebellum | Lower back of the brain ("little brain") | Balance, posture, and the coordination of precise, learned movements (e.g. playing a musical instrument, typing) |
| Medulla oblongata (medulla) | Base of the brain, continuous with the spinal cord | Automatic (autonomic) control of heart rate, breathing rate, and blood pressure |
Remember: the cerebral cortex handles what you consciously choose to do; the cerebellum makes those movements smooth and coordinated; the medulla keeps you alive automatically without conscious effort.
How do scientists map the functions of the brain?
Several methods allow neuroscientists and doctors to investigate which brain regions control which functions:
Lesion studies (studying brain damage)
Patients who have suffered strokes, tumours, or injuries to specific brain regions show predictable losses of function depending on the area affected. This was the earliest evidence for localisation of brain function. The famous case of Phineas Gage (a 19th-century railway worker who survived a metal rod passing through his frontal lobe) showed that damage to the frontal cortex dramatically changes personality — an early clue to the cortex's role in behaviour.
Electrical stimulation
During some brain surgeries, neurosurgeons stimulate specific areas of the exposed cortex with a small electrical probe while the patient is awake. The patient reports sensations or makes movements depending on which area is stimulated, allowing the surgeon to identify functional areas before removing tumour tissue. This method mapped the sensory and motor cortex in detail.
MRI scanning (Magnetic Resonance Imaging)
Functional MRI (fMRI) measures changes in blood flow to different brain regions while a patient is performing a task (reading, looking at images, solving problems). Active brain regions require more oxygen, so blood flow increases there. fMRI produces detailed three-dimensional maps of brain activity in real time, without any radioactivity or surgery. It is the primary tool for modern neuroscience research.
CT and PET scanning
CT scans use X-rays to image brain structure (identifying tumours, bleeding, or structural damage). PET scans use a radioactive tracer that concentrates in active regions, showing metabolic activity in the brain.
Why is the brain difficult to treat medically?
The brain presents unique challenges for medical treatment:
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Blood-brain barrier: Specialised cells surrounding the brain's blood vessels form a tight "barrier" that prevents many drugs and substances from passing from the blood into brain tissue. This protects the brain from toxins but also prevents many potentially therapeutic drugs from reaching their targets. Designing drugs small enough and lipid-soluble enough to cross the barrier is a major challenge in neuropharmacology.
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Neurones do not readily regenerate: Unlike most other body cells, mature neurones in the adult brain and spinal cord have very limited capacity to divide and replace damaged cells. When neurones die (as in a stroke or Alzheimer's disease), those cells and the functions they performed are generally lost permanently.
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Extreme complexity: The brain contains approximately 100 billion neurones, each forming on average 7,000 synaptic connections with other neurones — giving a total of around 700 trillion synapses. The connectivity is so intricate that surgery carries significant risks: removing a tumour may unavoidably damage functioning neural tissue nearby, potentially causing permanent loss of speech, movement, or memory.
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Lack of pain receptors: The brain itself has no pain-sensitive nociceptors. Headaches arise from pain-sensitive structures surrounding the brain (meninges, blood vessels, muscles). This means patients can remain conscious during some brain surgery, enabling the electrical stimulation mapping described above, but it also means brain disease often causes no pain and goes undetected until significant damage has occurred.
What are some common brain conditions examined at GCSE?
| Condition | Cause | Effect |
|---|---|---|
| Stroke | Interrupted blood supply to part of the brain (blocked or ruptured vessel) | Loss of speech, movement, or sensation depending on which area is affected |
| Brain tumour | Uncontrolled division of brain or adjacent cells | Pressure on brain tissue; symptoms depend on location |
| Alzheimer's disease | Progressive degeneration of neurones, with plaques and tangles | Memory loss, personality change, decline in cognitive function |
| Epilepsy | Abnormal, synchronised electrical activity in the brain | Seizures; can often be controlled with medication |
Frequently asked questions
What is the difference between the cerebellum and the cerebral cortex?
The cerebral cortex is responsible for conscious, voluntary activities — thinking, speaking, reading, planning, and intentional movement. It is the seat of intelligence, personality, and sensory experience. The cerebellum, by contrast, operates largely below the level of consciousness: it coordinates and fine-tunes movements initiated by the motor cortex, ensuring they are smooth, accurate, and well-timed. If your cerebellum were damaged, you would still be able to decide to walk, but the execution would be clumsy and uncoordinated — you would stumble, unable to balance properly.
How does fMRI show which part of the brain is active?
fMRI measures the BOLD signal (blood-oxygen-level-dependent signal). When a brain region becomes active, its neurones consume more oxygen and glucose. The local blood vessels dilate and increase blood flow to meet this demand. Oxygenated blood (oxyhaemoglobin) and deoxygenated blood (deoxyhaemoglobin) have different magnetic properties, and the fMRI scanner detects this difference. Regions with increased blood flow (increased oxyhaemoglobin) appear brighter on the fMRI image. By scanning a participant performing a specific task and subtracting the brain activity at rest, researchers can produce maps showing exactly which brain regions are activated by that task.
Why can't damaged brain tissue repair itself like a broken bone can?
Bone cells (osteoblasts) and most other body cells retain the ability to divide and produce new cells to replace damaged ones. Most mature neurones in the adult brain have exited the cell cycle — they are terminally differentiated and do not divide. Research into stem cells and neurogenesis (new neurone production) in adults has shown that some brain regions (notably the hippocampus, involved in memory) do produce some new neurones throughout life, but this is insufficient to repair significant damage. This is why strokes cause permanent disability rather than a temporary loss of function: the dead neurones cannot be replaced, and while the brain can partially reorganise itself (neuroplasticity), it cannot restore full function in many cases.
What is the role of the medulla in breathing?
The medulla oblongata contains the respiratory centre — a group of neurones that generates the automatic rhythmic signals for breathing. These signals travel via motor neurones to the diaphragm and intercostal muscles, causing them to contract (inhale) and relax (exhale) roughly 12–20 times per minute at rest. The respiratory centre monitors CO₂ levels in the blood (via chemoreceptors in the medulla and in the aorta and carotid arteries). When CO₂ rises (as it does during exercise), the medulla increases the breathing rate and depth automatically — without conscious effort. This is why you do not need to remember to breathe during sleep.
For Socratic GCSE biology with Professor Darwin — tracing a nervous impulse from receptor to brain to effector — visit aitutors.me.