Drugs and the nervous systemEdexcel A-Level Biology B: Mind map

Exam questions on Drugs and the nervous system

1. Nicotine from tobacco smoke reaches the brain and the junctions between motor neurones and muscles, where acetylcholine is the transmitter. The shape of the nicotine molecule is similar to that of acetylcholine.
   Explain why nicotine can cause a postsynaptic neurone to fire an action potential when no acetylcholine has been released.2 marks
2. A dentist injects lidocaine, a local anaesthetic, close to a sensory nerve in a patient's jaw before filling a tooth. Lidocaine enters the sensory neurones. While the anaesthetic lasts, the patient feels no pain from the tooth, even though the pain receptors there are still stimulated by the drill.
   Explain why the patient feels no pain.2 marks
3. A man is bitten by a cobra. Within an hour his muscles weaken and he has difficulty breathing. Cobra venom contains a toxin that binds to acetylcholine receptors on the postsynaptic membrane at neuromuscular junctions without opening the channel. In a laboratory, a motor neurone and its muscle are stimulated electrically, and the maximum force of muscle contraction is recorded. Before the venom is added the force is 5.0 N, and 10 minutes after the venom is added it is 1.0 N.
   Explain why the man's muscles became weak and he had difficulty breathing.3 marks