A level-readyAll subjects · Biology · WBI15 (Unit 5)
The brain and brain imaging
Different brain regions have different jobs. Scanning techniques let doctors see the brain's structure and activity without surgery.
Brain regions
The brain is part of the central nervous system. Its main regions each coordinate different functions.
| Region | Location | Main functions |
|---|---|---|
| Cerebral hemispheres (cerebrum) | Large folded outer layers, left and right | Conscious thought, memory, language, interpreting sensory information, voluntary movement |
| Hypothalamus | Below the cerebrum, above the pituitary | Homeostasis: thermoregulation, osmoregulation (osmoreceptors); controls the pituitary |
| Pituitary gland | Below the hypothalamus | Releases hormones such as ADH (posterior) and controls other glands |
| Cerebellum | Back of the brain, below the cerebrum | Balance, posture and coordination of smooth, precise movement |
| Medulla oblongata | Brain stem, joining the spinal cord | Automatic control of heart rate, breathing rate and blood pressure |
Imaging the brain
- CT (computed tomography): X-rays pass through the head from many angles and a computer builds cross-sectional images. Good for detecting bleeding, tumours and damage after a stroke; quick, but uses ionising radiation; shows structure, not activity.
- MRI (magnetic resonance imaging): a strong magnetic field and radio waves detect hydrogen nuclei in water. Gives detailed images of soft tissue, such as tumours or damage to myelin (as in multiple sclerosis). No ionising radiation, but noisy, slow and not suitable for people with metal implants.
- fMRI (functional MRI): detects changes in blood oxygen and blood flow (oxygenated and deoxygenated haemoglobin respond differently to the magnetic field). Active regions use more oxygen, so fMRI shows which areas are active during a task.
- PET (positron emission tomography): a radioactive tracer, such as labelled glucose, is injected; active areas take up more. Shows metabolic activity, for example reduced activity in Alzheimer's disease, or tumours.
Using imaging
Structural scans (CT and MRI) show where damage or a tumour is. Functional scans (fMRI and PET) show which areas are active, so they help researchers link regions to functions, such as language or memory, and help doctors diagnose conditions that change brain activity.
Worked example
A researcher wants to find which part of the brain is active when people recognise faces. Which scan should be used and why?
- The aim is to see activity, not just structure.
- fMRI detects increased blood flow and oxygen use in active areas.
- It uses no ionising radiation, so tasks can be repeated.
Answer: fMRI, because it shows which areas become more active during the task, without radiation.
Check yourself
- Which region coordinates balance and fine movement?
- Medulla oblongata
- Hypothalamus
- Pituitary gland
- Cerebellum
Show answer
Cerebellum. The cerebellum smooths and coordinates movement.
- Which brain region controls breathing rate automatically?
- Cerebellum
- Medulla oblongata
- Cerebral hemispheres
- Pituitary gland
Show answer
Medulla oblongata. The medulla contains the ventilation and cardiovascular centres.
- Which region is responsible for conscious thought and language?
- Medulla oblongata
- Cerebellum
- Hypothalamus
- Cerebral hemispheres
Show answer
Cerebral hemispheres. The cerebrum handles higher functions.
- How does a CT scan produce images?
- X-rays are passed through the head from many angles and a computer builds cross-sections
- Strong magnets detect hydrogen nuclei
- A radioactive tracer is injected
- Ultrasound echoes are recorded
Show answer
X-rays are passed through the head from many angles and a computer builds cross-sections. CT uses X-rays.
- What does fMRI detect?
- Bone density
- Radioactive glucose
- Changes in blood oxygen and flow in active brain areas
- Electrical activity of single neurones
Show answer
Changes in blood oxygen and flow in active brain areas. Active regions use more oxygen.
- Which technique uses a radioactive tracer to show active brain areas?
- PET
- MRI
- CT
- fMRI
Show answer
PET. Positron emission tomography uses tracers such as labelled glucose.
- Which is an advantage of MRI over CT?
- It is quicker and quieter
- It is suitable for people with metal implants
- It uses no ionising radiation and shows soft tissue in detail
- It shows brain activity directly
Show answer
It uses no ionising radiation and shows soft tissue in detail. MRI uses magnetic fields, not X-rays.
Sources
Last updated 7 November 2026. Spotted a mistake? Tell us.