A doctor investigates a person's withdrawal reflex. During the test, a blunt probe applies painful pressure briefly to the sole of the foot.
Electrodes record electrical impulses at two positions on the same sensory neurone. Position A is close to the receptor in the foot. Position B is where the sensory neurone enters the spinal cord. The part of the sensory neurone after position B, the relay neurone, the motor neurone and the leg muscle that pulls the foot away all work normally.
| Observation | Result |
|---|---|
| electrical impulse recorded at position A | yes |
| electrical impulse recorded at position B | no |
| leg muscle contracts | no |
Explain these results and what would happen if an electrical impulse were introduced into the sensory neurone at position B so that it travelled into the spinal cord.
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.