What you need to know
- 8.7Drugs act on impulse transmission: nicotine, lidocaine, cobra venom alpha toxin, L-DOPA in Parkinson’s disease, and MDMA.
No doses, no advice, and no description of how to obtain or use a drug. Parkinson’s is a loss of dopamine neurones in the substantia nigra. L-DOPA is not a cure. MDMA is illegal and harmful. Serotonin detail is also 8B 4.
By the end, you should be able to…
- Match each named substance to a synapse or a sodium channel.
- Explain why L-DOPA can raise brain dopamineA neurotransmitter in the brain involved in movement, reward and motivation. when dopamine itself is a poor drug for that purpose.
- Keep every example as a mechanism, not a recommendation.
Build your understanding
Acetylcholine synapses can be mimicked or blocked
Nicotine is a similar shape to acetylcholineA neurotransmitter used at many synapses and at neuromuscular junctions.. It binds nicotinic acetylcholine receptors on the next membrane and stimulates that cell. Acetylcholinesterase does not break nicotine down, so the stimulation lasts longer than a normal pulse of acetylcholine. That is the transmission effect. Addiction and harm are real. They are not a reason to describe use.
Cobra venom alpha toxin also binds acetylcholine receptors, but it blocks them. At the neuromuscular junction the muscle membrane cannot be depolarised, so the muscle cannot contract. Paralysis can include the muscles of breathing. The toxin is an antagonist. Nicotine, in the teaching comparison, is an agonist. Do not swap them.
Lidocaine stops the spike
Lidocaine blocks voltage-gated sodium channels in the neurone membrane where it is applied. Sodium cannot enter, so action potentialA rapid reversal of the potential difference across a neurone membrane, caused by Na⁺ ions flowing in, then K⁺ ions flowing out. are not conducted past that region. Pain impulses from a local area do not reach the central nervous systemThe brain and spinal cord.. This is a local anaesthetic action. It is not a whole-brain sedative in this specification point, and it is not an acetylcholine story.
A dentist’s injection is a medical use under professional control. Do not invent a dose or a home method. The biology is the closed sodium channel.
L-DOPA and MDMA act on brain transmitters
Parkinson’s disease involves the loss of nerve cells in the substantia nigra that release dopamineA neurotransmitter in the brain involved in movement, reward and motivation., so dopamine signalling falls. Movements become slow, muscles can be stiff, and there may be tremor. Dopamine given as a drug does not readily enter the brain. L-DOPA does cross the blood-brain barrier and can be converted to dopamine in remaining cells, so transmission at those synapses can improve. It does not replace the dead neurones. It is not a cure, and this page is not a treatment plan.
L-DOPA and MDMA act on brain transmitters (continued)
MDMA increases the release of serotoninA neurotransmitter in the brain involved in mood, sleep and appetite. in brain synapses and reduces its reuptake, so more serotonin is in the cleft and mood and perception change. It can also affect other transmitters. The specification point is that synaptic effect. MDMA is harmful and illegal. Do not add a dose, a route, or any suggestion of use. Depression and serotonin are treated more carefully in 8B 4. Do not say MDMA is a depression medicine.
NOT: no dose is required, and MDMA is not a depression medicine.
- Nicotine is an agonist at the acetylcholine receptor
- Cobra toxin blocks that receptor
- Lidocaine blocks sodium channels
- L-DOPA is a precursor, not dopamine itself
Two traps this diagram blocks
- Do not swap nicotine and the cobra toxin.
- Do not describe lidocaine as an acetylcholine drug.
From the diagram alone
Question
Compare how nicotine and cobra venom alpha toxin affect the acetylcholine receptor, and state one different site used by lidocaine. [4]
Show a model answer
Nicotine stimulates the receptor and is not broken down by acetylcholinesterase. The toxin binds the receptor and blocks it, so the muscle cannot contract. Lidocaine instead blocks voltage-gated sodium channels, so the action potential fails.
| Substance | Where it acts | Effect on transmission |
|---|---|---|
| Nicotine | Acetylcholine receptor | Stimulates; not broken down by the esterase |
| Cobra alpha toxin | Acetylcholine receptor on muscle | Blocks; muscle cannot contract |
| Lidocaine | Voltage-gated sodium channel | Stops action potentials locally |
| L-DOPA | Converted to dopamine in the brain | Raises dopamine signalling; not a cure |
| MDMA | Serotonin release and reuptake | More serotonin in the cleft; harmful |
Make your reasoning visible
Agonist or blocker
Nicotine stimulates the acetylcholineA neurotransmitter used at many synapses and at neuromuscular junctions. receptor. The cobra toxin blocks it. Lidocaine is a sodium-channel block, a third site.
L-DOPA is the precursor
Say why dopamineA neurotransmitter in the brain involved in movement, reward and motivation. itself is a poor substitute: it does not readily cross into the brain.
Avoid this misconception
The claim: Lidocaine blocks acetylcholine, and L-DOPA is the same molecule as dopamine.
The correction: Lidocaine blocks sodium channels so the impulse cannot pass. L-DOPA is a precursor that can enter the brain and be converted into dopamine.
Check your understanding
Try each question before opening the suggested answer.
Check your understanding (continued)
Practice question
Retrieval and explanation · suggested answer
How does lidocaine prevent a pain impulse from travelling?
Show suggested answer
It blocks voltage-gated sodium channels, so the membrane cannot depolarise and an action potential is not conducted.
Practice question
Retrieval and explanation · suggested answer
How does cobra venom alpha toxin cause paralysis?
Show suggested answer
It binds and blocks acetylcholine receptors on the muscle, so acetylcholine cannot depolarise the muscle membrane.
Practice question
Retrieval and explanation · suggested answer
Why is L-DOPA used rather than dopamine itself in Parkinson’s disease?
Show suggested answer
L-DOPA can cross the blood-brain barrier and be converted to dopamine. Dopamine does not readily enter the brain. Cells that make dopamine have been lost in the substantia nigra.
Practice question
Retrieval and explanation · suggested answer
What does MDMA do at a serotonin synapse?
Show suggested answer
It increases serotonin release and reduces reuptake, so more serotonin remains in the synaptic cleft.
Take the idea further
Apply the same specification knowledge to an unfamiliar problem. Any extra assumptions are supplied in the question.
Stretch question
A substance binds acetylcholine receptors on skeletal muscle and nothing contracts. A second substance binds the same family of receptors on a brain neurone and the next cell fires repeatedly. Which specification example fits each, and why is lidocaine not a third member of this pair?
Show a hint
Block versus stimulate. Then change the protein.
Explore the reasoning
The muscle blocker fits cobra venom alpha toxin. The repeated firing fits nicotine, which is not destroyed by acetylcholinesterase. Lidocaine acts on voltage-gated sodium channels, not on the acetylcholine receptor, so it is a different mechanism even though it also stops signals.
Recall this lesson
Lesson recall questions
Question 1 of 5: State how nicotine affects a cholinergic synapse.
Drugs on synapses
Practice question
Retrieval and explanation · suggested answer
State how nicotine affects a cholinergic synapse.
Lesson: 8A 4: The Effect of Drugs on the Nervous System
Try this from memory first.
Put your biology to work
Explore where these ideas appear in the world. Enrichment, not extra required recall.
The NHS account of Parkinson’s is the cell loss
8A · The Effect of Drugs on the Nervous SystemThe NHS says Parkinson’s disease is caused by a loss of nerve cells in the substantia nigra, which reduces dopamine, and that people may have tremor, slow movement…Specification 8.7Read & use the scienceClose article
Why this matters
The NHS says Parkinson’s disease is caused by a loss of nerve cells in the substantia nigra, which reduces dopamine, and that people may have tremor, slow movement and stiff muscles. That supports the reason L-DOPA exists in the specification. The page is a health overview. It is not a dose chart, and it does not describe nicotine, lidocaine or MDMA. 8.7: L-DOPA is used because dopamine signalling has fallen. The other four substances are different synaptic or channel effects.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.7 How specified drugs alter nerve impulse transmission.
Use the science
Why is “the NHS says take L-DOPA with MDMA” an unacceptable sentence?
Explore a possible response
The NHS page describes the disease, not a combination with MDMA. MDMA is not a treatment. This lesson only explains mechanisms. Medical decisions belong with a clinician, not a revision note.
Explore the source
One receptor, very different chemicals
8A · The Effect of Drugs on the Nervous SystemAn NCBI neuroscience chapter describes the nicotinic acetylcholine receptor as a ligand-gated channel that can bind acetylcholine, nicotine and certain toxins. That helps explain why substances with very…Specification 8.7Read & use the scienceClose article
Why this matters
An NCBI neuroscience chapter describes the nicotinic acetylcholine receptor as a ligand-gated channel that can bind acetylcholine, nicotine and certain toxins. That helps explain why substances with very different origins can interfere at a synapse: they interact with the same protein but do not necessarily cause the same response. A toxin that prevents receptor activation can stop the usual postsynaptic change, while an agonist can mimic part of the neurotransmitter’s effect. The 8.7 examples require mechanism, not a list of frightening names. Concentration, receptor location and exposure route also matter for any real-world effect.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.7 How specified drugs alter nerve impulse transmission.
Use the science
Why would a toxin that blocks acetylcholine binding at a neuromuscular junction weaken muscle contraction?
Explore a possible response
The motor neurone can release acetylcholine, but the postsynaptic receptor cannot be activated normally. The muscle fibre receives a weaker or absent signal to begin contraction.
Explore the source
- Cholinergic receptorsNeuroscience, NCBI Bookshelf