Scientists use a computer model of a blinking reflex caused by an object moving towards the eye. The pathway contains receptors in the eye, a sensory neurone, a relay neurone in the brain, a motor neurone and an eyelid muscle.
Two altered models, X and Y, each have one blocked component. All the other components work normally.
| observation | model X | model Y |
|---|---|---|
| receptors in the eye convert the stimulus into an impulse | yes | yes |
| an impulse is recorded where the sensory neurone enters the brain | yes | no |
| neurotransmitter is released from the end of the relay neurone | yes | no |
| a new impulse starts in the motor neurone | no | no |
| the eyelid closes when the relay neurone is stimulated | no | yes |
| the eyelid closes when the motor neurone is stimulated | yes | yes |
In a separate investigation, the scientists compare the blinking reflex with a blink chosen after a person sees a light signal. They run each pathway with normal myelin and with damaged myelin.
| response | condition of myelin | mean response time in s |
|---|---|---|
| blinking reflex | normal | 0.10 |
| blinking reflex | damaged | 0.17 |
| consciously chosen blink | normal | 0.24 |
| consciously chosen blink | damaged | 0.31 |
Explain which part of the pathway is blocked in model X.
Explain which component is blocked in model Y.
Explain the patterns in the response-time data.
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.