effects of drugs on CNS + NT

• what are neurotransmitters


  chemical messengers which act between neurons
• what can NTs be, depending on what

  excitatory or inhibitory, depending on the effect they have on neighbouring neurons
• what does serotonin do, how

  causes inhibition in postsynaptic neuron by making it more negatively charged and less likely to fire
• what does dopamine do

  causes excitation of postsynaptic neuron by increasing its positive charge and making it more likely to fire
• what is summation


  the adding together of excitatory and inhibitory signals
• why does summation happen

  neurons can receive both types of signals but the overall effect and firing will depend on the overall 'charge' on the neuron
• what is the main reward pathway in humans

  the mesocorticolimbic pathway
• what does this pathway cause

  causes us to experience pleasant/rewarding feelings, encourages us to repeat behaviours
• what does the pathway operate on

  dopamine
• what things can 'hijack' the system

  drugs
• how do stimulants work

  they increase NT activity in the brain as they increase the amount of dopamine in the synaptic cleft by blocking their reuptake = there is a prolonged effect of NT in the postsynaptic neuron
• examples of stimulants


  cocaine, amphetamines
• how do depressants work

  decrease NT activity. increase the activity of GABA which binds to glutamate receptors to prevent glutamate binding = decreased effect of glutamate
• example of depressant


  alcohol
• how do hallucinogens work

  act on serotonin receptors to release more serotonin in different brain areas
• what is the first stage of the addiction withdrawal cycle

  drug is taken = increased dopamine in brain in reward pathway = feel good = brain reacts to sudden increase in dopamine downregulates its natural production of it
• second stage of addiction withdrawal cycle

  drug effects wear off = person has less dopamine than usual = feels slow and depressed = motivates person to take more
• third stage of addiction withdrawal cycle

  more drug is taken to reproduce first feeling = repeated use has led to further downregulation of dopamine production = brain no longer operates normally = has to take more drug to feel the normal
• fourth stage of addiction withdrawal cycle

  person stops taking drug = lack of dopamine = feel low and depresses (withdrawal) = keeps taking drug to avoid this (addiction)
• evidence for drug effects

  research supporting dopamine: animal research - damaging the mesocorticolimbic pathway in mice = neurons were unable to produce the dopamine normally felt in reward = mice fail to self administer cocaine as they don't need to feel rewarded by the dopamine reaction. = cocaine effects are due to activity of dopamine in reward system
• counterargument of the evidence

  using animals in research - differences arise as the human brain is more complex than the mouse brain so is hard to generalise the findings to humans, isolating effects of just one NT oversimplifies the process