Brain chemistry, drugs and diseaseEdexcel A-Level Biology A: Mind map

Exam questions on Brain chemistry, drugs and disease

1. A 68-year-old man has a tremor in his hands, stiff muscles and slow movement. A brain scan shows that many of the neurones in a region called the substantia nigra, which normally release the neurotransmitter dopamine, have died. He is diagnosed with Parkinson's disease and prescribed L-Dopa.
   Explain how L-Dopa reduces the symptoms of Parkinson's disease.2 marks
2. A patient with depression is prescribed fluoxetine, a selective serotonin reuptake inhibitor (SSRI). Studies suggest that in some people with depression the concentration of serotonin in certain synapses in the brain is lower than normal. Fluoxetine binds to the transporter proteins in the presynaptic membrane that normally take serotonin back into the presynaptic neurone.
   Suggest why blocking reuptake makes it more likely that an action potential will be generated in the postsynaptic neurone.2 marks
3. MDMA (ecstasy) has a molecular shape similar to serotonin. In an experiment on rats, the concentration of serotonin in the synaptic clefts of one brain region was measured before and one hour after a dose of MDMA. It rose from 1.0 to 6.5 arbitrary units. Users of MDMA often report feeling happy and energetic for some hours, followed by low mood for several days.
   Describe how MDMA increases the concentration of serotonin in a synaptic cleft.3 marks