Edexcel IGCSE Biology 2.89 synapses and neurotransmitters
Practise explaining why impulses slow across neurone pathways when synapses and neurotransmitter diffusion are involved.
- Syllabus
- First assessment 2019
- Course
- Biology 4BI1
Exam points
- explain slower pathway speeds by referring to synapses, gaps and neurotransmitter diffusion
2.89 Neurotransmitters at synapses question 1
Multiple sclerosis is a condition that can slow down the speed at which electrical impulses travel along neurones.
The time taken for the blink reflex to occur can be used to help diagnose if someone has multiple sclerosis.
The blink reflex causes the eyelid to close.
Air is blown on to the eye and the time taken for the eyelid to close is recorded.
The diagram shows the reflex pathway.
The speed the impulse moves along the reflex arc consisting of all three neurones in a person without multiple sclerosis is 77 metres per second.
The time taken for the blink reflex to occur in a person with multiple sclerosis is 0.0050 s .
The total length of the neurones in the reflex arc for the person with multiple sclerosis is 25 cm .
The speed of an impulse along the axon of the motor neurone for someone without multiple sclerosis is 120 metres per second.
Suggest why the speed of the impulse calculated along all three neurones is less than the speed of the impulse along only the motor neurone.
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