B25: The Brain
Brain regions including cerebral cortex, cerebellum and medulla, CT and PET scanning techniques, and difficulties investigating and treating brain damage for GCSE Biology Higher.
Key Definitions
- Cerebral cortex – the outer layer of the cerebrum; responsible for consciousness, intelligence, memory, and language.
- Cerebellum – the region of the brain responsible for balance and coordination of muscle activity.
- Medulla oblongata – the region of the brain that controls unconscious activities such as breathing and heart rate.
- CT scan – computed tomography; uses X-rays to produce a detailed image of brain structure.
- PET scan – positron emission tomography; uses radioactive glucose to show active areas of the brain.
Main Regions of the Brain
| Brain Region | Function | Key Details |
|---|---|---|
| Cerebral cortex | Consciousness, intelligence, memory, language, and voluntary actions | The outer layer of the cerebrum; highly folded to increase surface area; divided into two hemispheres |
| Cerebellum | Balance and muscle coordination | Located at the back and base of the brain; controls fine motor movements and posture |
| Medulla oblongata | Unconscious activities: breathing, heart rate, swallowing | Located at the base of the brain, connecting to the spinal cord; controls autonomic processes |
Worked Example 1 – Brain Region Functions
Question: A patient has damage to their cerebellum. What symptoms would you expect and why?
Solution: Damage to the cerebellum would primarily affect balance and muscle coordination. The patient would likely have difficulty walking steadily, performing precise movements (e.g. touching their finger to their nose), and maintaining posture. They may appear clumsy and uncoordinated because the cerebellum normally fine-tunes muscle movements and coordinates different muscle groups. Their voluntary movement would still be controlled by the cerebral cortex, but the movements would be jerky and poorly coordinated without the cerebellum.
Worked Example 2 – The Medulla and Automatic Control
Question: When carbon dioxide levels in the blood increase during exercise, the breathing rate increases. Explain the role of the medulla in this process.
Solution: Receptors in the blood vessels detect the increase in carbon dioxide concentration. This information is sent to the medulla oblongata, which acts as the coordinator. The medulla sends nerve impulses via the autonomic nervous system to the diaphragm and intercostal muscles (the effectors), causing them to contract more frequently and more forcefully. This increases the breathing rate and depth, allowing more CO2 to be exhaled and more O2 to be inhaled. Once CO2 levels return to normal, the medulla reduces the stimulation. This is an example of negative feedback and automatic (unconscious) control.
Brain Scanning Techniques
| Technique | How It Works | What It Shows | Advantages | Limitations |
|---|---|---|---|---|
| CT scan | Uses X-rays to create cross-sectional images | Brain structure – can show tumours, bleeding, and damage | Quick, detailed structural images | Cannot show brain function; involves ionising radiation |
| PET scan | Uses radioactive glucose tracer; active areas show up brighter | Brain function – shows which areas are active during tasks | Shows brain activity in real time | Less detailed structure; uses radioactive tracer; expensive |
Worked Example 3 – CT vs PET Scans
Question: A doctor suspects a patient has a brain tumour. A scientist wants to identify which brain areas are active during speech. Which scanning technique should each use and why?
Solution: The doctor should use a CT scan because it produces detailed images of brain structure and can reveal the location and size of a tumour. The scientist should use a PET scan because it shows brain function and activity. By asking the participant to speak while undergoing a PET scan, the scientist can identify which areas of the brain become active (use more glucose) during speech production. A CT scan would not show this functional activity.
Difficulties Investigating the Brain
- Complexity: The brain contains billions of neurones with trillions of connections. Understanding how these all work together is enormously difficult.
- Delicacy: Brain tissue is very delicate and easily damaged. Surgery carries high risks of causing further damage.
- Inaccessibility: The brain is encased in the skull, making it physically difficult to access. Surgeons must cut through the skull and navigate through brain tissue.
Treating Brain Damage
Brain damage is particularly difficult to treat because:
- Limited regeneration: Most neurones in the brain and spinal cord do not regenerate once damaged. Unlike skin or liver cells, neurones cannot easily divide and replace lost cells.
- Risk of further damage: Surgical treatment can cause additional damage to surrounding healthy tissue.
- Scar tissue: Damage to the brain can cause scar tissue to form, which may interfere with normal electrical signalling.
Current approaches include drug treatments to manage symptoms, physical therapy and rehabilitation to train other brain areas to take over lost functions (brain plasticity), and experimental stem cell treatments.
Worked Example 4 – Why Brain Damage Is Hard to Treat
Question: Explain why damage to the brain is much harder to treat than damage to the skin or liver.
Solution: Brain damage is harder to treat for several reasons. First, neurones in the brain have very limited ability to regenerate, unlike skin or liver cells which can divide and replace damaged tissue. Second, the brain is encased in the skull, making surgical access difficult – any operation risks causing further damage. Third, the brain is highly complex with billions of interconnected neurones, so even small amounts of damage can disrupt many functions. Fourth, drugs cannot easily reach the brain because of the blood-brain barrier. In contrast, skin cells divide rapidly to heal wounds, and the liver has a remarkable capacity to regenerate.
Practice Questions
Higher
Q1. Name three regions of the brain and state the function of each.
Show Answer
Cerebral cortex – responsible for consciousness, intelligence, memory, and language. Cerebellum – responsible for balance and muscle coordination. Medulla oblongata – controls unconscious activities such as breathing rate and heart rate.
Higher
Q2. Explain the difference between a CT scan and a PET scan, and state when each would be used.
Show Answer
A CT scan uses X-rays to produce detailed images of brain structure. It is used to identify structural problems such as tumours, bleeding, or physical damage. A PET scan uses a radioactive glucose tracer to show which areas of the brain are most active. It is used to study brain function and identify which areas are involved in specific tasks. CT shows structure; PET shows function.
Higher
Q3. Describe three reasons why it is difficult to investigate and treat the brain.
Show Answer
1. Complexity – the brain contains billions of neurones with trillions of connections, making it extremely difficult to understand how everything works together. 2. Delicacy – brain tissue is easily damaged, and surgery carries a high risk of causing further damage. 3. Limited regeneration – neurones in the brain do not regenerate once damaged, so any damage is largely permanent.
Higher
Q4. A patient has damage to their medulla. Explain why this is life-threatening.
Show Answer
The medulla controls vital unconscious activities including breathing rate and heart rate. Damage to the medulla could disrupt these automatic processes, meaning the body may not be able to regulate breathing or heart function. Both of these functions are essential for life, which is why damage to the medulla is often fatal.
Higher
Q5. Suggest why stem cell research might be important for treating brain damage in the future.
Show Answer
Neurones in the brain have very limited ability to regenerate, so damaged brain tissue does not easily repair itself. Stem cells can differentiate into different types of cells, so they could potentially be used to replace damaged neurones and restore lost brain function. This offers hope for treating conditions that are currently incurable, such as paralysis from spinal cord injury or brain damage from stroke.
Exam Tips
- This is a Higher only topic.
- Always match the correct function to the correct brain region – cortex is for consciousness and intelligence, cerebellum for balance, medulla for unconscious processes.
- CT = structure; PET = function. This is a very common exam distinction.
- When asked about difficulties treating the brain, mention at least three of: complexity, delicacy, inaccessibility, and limited regeneration.
- Don't confuse the cerebellum (balance/coordination) with the cerebral cortex (intelligence/memory).
🔢 Maths Skills
Mathematical Skills
Minimal maths in this topic, but you may need to interpret data from brain scan studies (e.g. comparing percentage changes in brain activity shown on PET scans) or calculate means from experimental data on reaction times or memory tests.
⚠️ Common Misconceptions
Watch Out!
1. Wrong: We only use 10% of our brain. Correct: Brain scans (PET and fMRI) show we use all of our brain — different areas are active during different tasks, and even at rest the brain is highly active.
2. Wrong: Brain damage is always permanent. Correct: Neuroplasticity means other brain areas can sometimes take over lost functions, especially in younger patients. Rehabilitation and therapy can support this rewiring.
✍️ 6-Mark Question
Extended Answer
6 marks: Explain why brain damage is difficult to treat and discuss ethical issues.
Brain damage is difficult to treat because neurones have very limited ability to regenerate, so damaged cells cannot easily be replaced. The brain is encased in the skull, making surgical access difficult and risky — operations may cause further damage to surrounding healthy tissue. The blood-brain barrier prevents many drugs from reaching the brain. The brain's enormous complexity, with billions of interconnected neurones, means even small damage can disrupt many functions. Ethical issues include: whether it is acceptable to use experimental treatments (e.g. stem cell implants) on patients who cannot give informed consent; the risk of causing further harm through surgery; and whether resources should be spent on expensive, uncertain treatments. There are also ethical concerns around using animal models for brain research and the storage and use of brain tissue samples.
Mark scheme: 1 mark for limited regeneration; 1 mark for skull/delicacy; 1 mark for blood-brain barrier or complexity; 1 mark for a specific ethical issue; 1 mark for a second ethical issue; 1 mark for balanced discussion or justification.
📊 AO3: Analyse & Evaluate
Analysis and Evaluation
A scientist used PET scans to compare brain activity in two groups: healthy volunteers and patients with brain damage. The damaged group showed 40% less activity in the damaged region but 15% more activity in adjacent areas. (a) Suggest what the increased activity in adjacent areas might indicate. (b) Evaluate the reliability of using PET scans to assess brain function — give one strength and one limitation. (c) Explain why it would be unethical to carry out this study without informed consent.
Answers: (a) Neuroplasticity — adjacent areas may be compensating for the damaged region by taking over some of its functions. (b) Strength: PET shows real-time brain activity during tasks. Limitation: it uses radioactive tracers, has limited spatial resolution, and is expensive, so sample sizes are often small. (c) Patients must understand the risks (radiation exposure, potential findings about their condition) and voluntarily agree — without consent, the study violates their autonomy and could cause psychological harm.
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