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Exam questions · Biology · The Nervous System

Scanning and Treating the Brain (Higher tier)

  • 6 exam questions
  • 22 marks
  • 9 quick checks
  1. 1 State [2 marks]

    State one difference between the information given by a CT scan and by a PET scan.

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    Model answer

    A CT scan shows the structure of the brain, whereas a PET scan shows its function, which means which areas are active.

    Mark scheme

    • CT shows structure — 1 mark
    • PET shows function / activity — 1 mark
  2. 2 Explain [3 marks]

    Explain why it is difficult for doctors to investigate the brain tissue inside the skull.

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    Model answer

    The brain is protected by the skull, so it is difficult to reach. It is made of soft, delicate tissue, so surgery to take a sample could damage it. The neurones are tiny and work together, so looking at the tissue does not show which parts are active.

    Mark scheme

    • Inside the skull / inaccessible — 1 mark
    • Delicate tissue easily damaged — 1 mark
    • Cannot see which areas are active — 1 mark
  3. 3 Describe [3 marks]

    Describe how a PET scan is used to find which parts of the brain are active.

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    Model answer

    The patient is injected with glucose that contains a radioactive tracer. The active parts of the brain use more glucose, so more tracer collects in them. Detectors around the head pick up the radiation, and a computer turns it into an image in which the active areas show up brightly.

    Mark scheme

    • Radioactive tracer injected — 1 mark
    • Active areas use more glucose and take up more tracer — 1 mark
    • Detectors build an image showing the active areas — 1 mark
  4. 4 Explain [4 marks]

    A patient has headaches and slurred speech. Explain how a CT scan and a PET scan could each help the doctors.

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    Model answer

    A CT scan could show the structure of the brain, for example a tumour or a bleed that is pressing on the area. A PET scan could show the function, so the doctors could see whether the area that controls speech is less active than normal, or whether a tumour is growing fast. Used together, they give a more complete picture.

    Mark scheme

    • CT shows the structure, such as a tumour — 1 mark
    • A tumour or bleed can explain the symptoms — 1 mark
    • PET shows the activity of the area — 1 mark
    • Together they give a fuller picture — 1 mark
  5. 5 Explain [4 marks]

    Explain why spinal injuries and brain tumours are difficult to treat.

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    Model answer

    Neurones in the brain and spinal cord do not regenerate well, so after a spinal injury the damage is permanent and the patient is paralysed below the injury. Brain tumours are difficult to remove because the tissue is delicate and the tumour may be near vital areas, so healthy tissue can be damaged. Many drugs also cannot cross from the blood into the brain.

    Mark scheme

    • Neurones do not regenerate — 1 mark
    • Spinal injury causes paralysis — 1 mark
    • Delicate brain tissue, close to vital areas — 1 mark
    • Drugs cannot always reach the brain — 1 mark
  6. 6 Evaluate [6 marks]

    Evaluate the use of CT and PET scans to investigate the brain.

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    Model answer

    Both scans let doctors see inside the head without surgery, which is much safer than opening the skull. A CT scan is quick and gives a detailed picture of the structure, so it is useful in emergencies and for finding tumours and bleeds, but it cannot show activity and uses X-rays. A PET scan shows which areas of the brain are active, so it can show how the brain works and how a disease changes it, but the picture is less detailed, it is expensive and the patient receives a radioactive tracer. Using both gives the most complete information, and the benefit of an accurate diagnosis usually outweighs the small risk from radiation.

    Mark scheme

    • Avoids the risk of surgery — 1 mark
    • CT: shows structure, fast — 1 mark
    • CT: limitation (only structure, X-rays) — 1 mark
    • PET: shows function — 1 mark
    • PET: limitation (radioactive, expensive, less detail) — 1 mark
    • A reasoned conclusion — 1 mark

Quick check

  1. 1

    Which scan uses X-rays to show the structure of the brain?

    1. ACT scan
    2. BPET scan
    3. CThermometer scan
    4. DBlood test
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    A: CT scan

    A CT scan uses X-rays from many angles to build an image of the brain's structure.

  2. 2

    Which scan shows which parts of the brain are active?

    1. ACT scan
    2. BPET scan
    3. CX-ray of the skull
    4. DUltrasound
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    B: PET scan

    A PET scan shows activity, because active neurones take up more of the radioactive glucose.

  3. 3

    What is injected into a patient before a PET scan?

    1. AIodine solution
    2. BInsulin
    3. CA radioactive tracer
    4. DA neurotransmitter
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    C: A radioactive tracer

    A radioactive tracer, usually a form of glucose, is injected and collects in the active areas of the brain.

  4. 4

    Why does the tracer collect in the active parts of the brain?

    1. AActive parts have fewer blood vessels
    2. BActive parts are warmer
    3. CThe skull attracts the tracer
    4. DActive neurones use more glucose
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    D: Active neurones use more glucose

    Active neurones respire faster and use more glucose, so more of the tracer is taken up.

  5. 5

    Why is it difficult to study brain tissue directly?

    1. AThe brain is too large
    2. BIt is inside the skull and easily damaged
    3. CThe brain has no neurones
    4. DThe brain has no blood
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    B: It is inside the skull and easily damaged

    The brain is protected by the skull and is delicate, so reaching it carries a risk of damage.

  6. 6

    What is the main problem with treating a spinal injury?

    1. ANeurones do not regenerate
    2. BScans cannot show the spinal cord
    3. CThe spinal cord has no neurones
    4. DImpulses travel too fast to treat
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    A: Neurones do not regenerate

    Neurones in the spinal cord do not regenerate well, so the damage is usually permanent.

  7. 7

    Why is it difficult to remove a brain tumour?

    1. ATumours are always cancerous
    2. BThe skull cannot be opened
    3. CIt may be next to vital areas and healthy tissue can be damaged
    4. DTumours cannot be seen on a scan
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    C: It may be next to vital areas and healthy tissue can be damaged

    Surgeons must avoid damaging healthy tissue and vital areas near the tumour.

  8. 8

    Which statement about CT scans is correct?

    1. AThey show which areas are active
    2. BThey use a radioactive tracer
    3. CThey cannot be used in emergencies
    4. DThey show the structure of the brain
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    D: They show the structure of the brain

    A CT scan shows structure, so it can show a tumour or a bleed, but not which areas are active.

  9. 9

    A doctor wants to know whether the speech area of a patient's brain is working normally. Which scan is best?

    1. ACT scan
    2. BPET scan
    3. CBoth show it equally
    4. DNeither can show it
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    B: PET scan

    A PET scan shows the function, which means how active an area is, so it can show whether the speech area is working normally.