Chemicals at synapses at Higher Level: An AHL statement: how pesticides and drugs change synaptic transmission.
Practise this as you read
- Describe how neonicotinoids act.
- Outline how cocaine acts.
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The big idea: Exogenous chemicals come from outside the body and can change synaptic transmission. Neonicotinoid pesticides bind the acetylcholine receptors of insects and are not broken down by acetylcholinesterase, so transmission is blocked. Cocaine blocks the reuptake of dopamine, so dopamine stays in the cleft and keeps stimulating the next neuron.
The points to remember
- Normally a neurotransmitter is removed after it acts.
- Neonicotinoids bind insect acetylcholine receptors.
- Acetylcholinesterase cannot break them down: transmission blocked.
- Cocaine blocks the reuptake transporters for dopamine.
- Dopamine stays in the cleft: the next neuron keeps being stimulated.
Remember it as: Stuck on the receptor, or stuck in the cleft.
Real example: bees and neonicotinoids. Neonicotinoids are taken up into the nectar and pollen of treated crops. Bees exposed to them can move less well and find their way home less often, which is why outdoor use of several neonicotinoids is banned in the European Union.
Trap: Cocaine does not bind the dopamine receptors; it blocks the reuptake transporters in the presynaptic membrane.
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How it is asked: Expect MCQs on how a named chemical acts, a Describe question on neonicotinoids, or the long Describe question on neurotransmitters and how chemicals disrupt them.
IB-style questionOutline[2 marks]
Outline how cocaine affects synaptic transmission.
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