Drugs and synaptic transmissionEdexcel International A Level Biology: Subtopic test

1. 1
   A dentist injects lidocaine into a patient's gum before removing a tooth. The patient feels pressure but no pain, and the numbness fades after about an hour.

   (a)

   What is the target of lidocaine in the sensory neurones?

   [1 mark]

   • AAcetylcholine receptors on the postsynaptic membrane
   • BAcetylcholinesterase in the synaptic cleft
   • CVoltage-gated sodium ion channels in the axon membrane
   • DVoltage-gated calcium ion channels in the presynaptic knob

   (b)

   Which statement correctly describes the effect of lidocaine on pain signals?

   [1 mark]

   • ANo action potentials are produced in the sensory neurones, so pain impulses do not reach the brain
   • BPain impulses reach the brain but the cerebral hemispheres ignore them
   • CThe sensory neurones fire continuously, so the brain cannot identify pain
   • DThe membrane of the sensory neurones stays depolarised and releases extra neurotransmitter

   (c)

   Explain, in terms of membrane potential, why the sensory neurones near the injection fail to transmit impulses.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A hiker is bitten by a cobra. Within an hour she has muscle weakness that progresses to paralysis, and she has difficulty breathing. The venom contains alpha toxin, which acts at neuromuscular junctions.

   (a)

   Where does alpha toxin act at the neuromuscular junction?

   [1 mark]

   • AOn voltage-gated calcium ion channels in the presynaptic knob
   • BOn acetylcholinesterase in the synaptic cleft
   • COn vesicles of acetylcholine inside the presynaptic knob
   • DOn acetylcholine receptors on the postsynaptic (muscle) membrane

   (b)

   Which statement correctly describes the effect of alpha toxin on the muscle fibre membrane?

   [1 mark]

   • ASodium ion channels are held open and the membrane stays depolarised
   • BSodium ion channels stay closed, so the membrane is not depolarised
   • CCalcium ion channels fail to open in the presynaptic membrane
   • DAcetylcholine builds up in the cleft because it is not broken down

   (c)

   Explain why the hiker has difficulty breathing.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A 68-year-old man with Parkinson's disease has a tremor, stiff muscles and slow movement. His neurologist prescribes L-DOPA for him rather than dopamine.

   (a)

   Explain why L-DOPA is prescribed rather than dopamine.

   [3 marks]

   (b)

   Explain how L-DOPA reduces the symptoms of Parkinson's disease, and why the dose may need to be increased after several years.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Drugs can alter synaptic transmission in different ways. Nicotine has a molecular shape similar to acetylcholine. Alpha toxin from cobra venom also binds to acetylcholine receptors. MDMA acts at synapses in the brain that use serotonin.

   (a)

   Compare the effects of nicotine and alpha toxin at a cholinergic synapse.

   [6 marks]

   (b)

   Explain how MDMA affects synaptic transmission at synapses that use serotonin, and suggest why regular users may later suffer from low mood.

   [6 marks]

   Total for question 4: 12 marks

End of questions