summation

• • Spatial summation - in which a number of different presynaptic neurons together release enough neurotransmitter to exceed the threshold value of the post synaptic neuron - new A.P is triggered 
• • Temporal summation - in which a single presynaptic neuron releases neurotransmitter many times over a very short period. If the concentration of neurotransmitter exceeds the threshold values of post synaptic neuron - new A.P is triggered 
• Effects of drugs on synapses:

  • Drugs interfere with normal synapse function….

   

  • Drugs interfere//block receptors - no Na+ enters post synaptic neuron
  • Neurotransmitters may not be synthesised 
  • Neurotransmitters may not be released from the vesicles in the presynaptic neurone 
  • Interaction between neurotransmitter and postsynaptic receptors may be affected e.g - bind to receptor 
  • Stimulatory by binding to receptors and opening sodium channels 
  • Inhibitory by blocking receptors & preventing binding