A patient has difficulty swallowing and can start a reaching movement, but the movement is poorly aimed.
A CT scan shows two areas of damaged tissue.
| Area | Position of damaged tissue |
|---|---|
| A | At the base of the brain, where the brain joins the spinal cord |
| B | At the back and base of the brain, underneath the cerebral hemispheres |
A PET scan is carried out while the patient completes two tasks. The results are compared with mean results from healthy people. Higher values indicate greater uptake of the tracer.
| Task | Area | Mean tracer uptake in healthy people (relative units) | Tracer uptake in the patient (relative units) |
|---|---|---|---|
| swallowing | A | 8.6 | 3.1 |
| reaching towards a target | A | 3.4 | 3.2 |
| swallowing | B | 4.2 | 4.0 |
| reaching towards a target | B | 9.1 | 4.1 |
Explain how the information from the two types of scan supports possible causes of the patient's symptoms and the limitations of the conclusions that can be drawn.
In your answer, refer to how each type of scan produces its information.
111 exam-style questions on Edexcel GCSE Biology 2.3 The nervous system and brain, covering 2.3.1 Structures and functions of the brain, 2.3.2 Imaging brain function with scanning, 2.3.3 Limitations in treating nervous system damage, 2.3.4 Neurones and impulse transmission, and 2.3.5 Structure and function of a reflex arc. Each one has a worked solution and a mark scheme showing where the marks go.