AQA A Level Biology

Revision Notes

6.2.9 Drug Effects on Synapses

Predicting the Effects of Drugs on a Synapse

  • Chemical or drugs can have a major impact on the functioning of the brain and nervous system
  • Some prescription drugs can have a beneficial effect on those suffering from neurological disorders while recreational drugs can have a damaging or even fatal effect
  • Many drugs have been found to produce a specific effect on synaptic transmission
  • They can have different modes of action such as:
    • Stimulating the release of a neurotransmitter
    • Providing the chemicals needed to synthesise neurotransmitters
    • Acting in the same way as a neurotransmitter by binding to the same specific receptor
    • Preventing the reuptake of the neurotransmitter by the presynaptic neurone
  • Research is ongoing to further understand how several drugs work in the hopes that they can be used to treat nervous disorders

Dopamine

  • There are many different neurotransmitters that bind to specific receptor molecules
  • They are often restricted to certain regions of the brain so that they have a specific function
  • Some are excitatory and some are inhibitory
    • Excitatory neurotransmitters result in the production of an action potential
    • Inhibitory neurotransmitters prevent the production of an action potential. They do this by causing potassium ions to leave the postsynaptic membrane
  • Dopamine is a neurotransmitter involved in muscle control
  • Individuals that suffer from Parkinson’s disease produce insufficient amounts of dopamine
  • There are two types of drugs that are used to treat this disease
    • A dopamine agonist – produces the same effect as dopamine by binding to the same receptors
    • A dopamine precursor – this can be used to synthesise dopamine in the neurones

Morphine

  • Dopamine also plays a vital role in pain relief
  • Chemicals called endorphins which are produced in the brain can stimulate the release of dopamine
  • The endorphins attach to opioid receptors found on presynaptic neurones that release dopamine molecules
    • Exercise is a natural way to cause the release of endorphins
  • Morphine is a chemical very similar in structure to endorphins and so it can provide pain relief by stimulating the release of dopamine

Cocaine

  • Cocaine also affects levels of dopamine
  • It binds to the dopamine transporter protein
  • This prevents dopamine from binding to the transporter so it is not able to move through the membrane back into the presynaptic neurone
  • As a result dopamine builds up in the synapses which can lead to feelings of pleasure

Cannabinoids

  • Cannabinoids are compounds found in cannabis
  • Cannabinoid receptors are located in the pre-synaptic membrane of neuromuscular junctions
  • When a cannabinoid molecule binds to its specific receptor, it closes the calcium ion channels
  • This leads to decreased muscle contraction
  • There is currently research investigating whether cannabinoids could be an effective drug in treating multiple sclerosis (MS)
    • MS is a disease that involves damage to the myelin sheaths of neurones. Sufferers struggle to control muscle contraction

MDMA

  • MDMA stimulates the release of multiple neurotransmitters most notably, serotonin
  • Serotonin can affect people in many ways including their mood, anxiety and sleep
  • When an individual takes MDMA they may feel extreme euphoria and enhanced touch and bodily sensations

Exam Tip

You don’t need to know the modes of action of any of the drugs mentioned above. However, you may be asked to read information given to you in the exam and use it to explain how a drug may work.

Author: Lára

Lára graduated from Oxford University in Biological Sciences and has now been a science tutor working in the UK for several years. Lára has a particular interest in the area of infectious disease and epidemiology, and enjoys creating original educational materials that develop confidence and facilitate learning.
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