Summation

• What happens if a stimulus is weak?

  Only a small amount of neurotransmitter will be released from a neurone into the synaptic cleft. This might NOT BE ENOUGH to excite the postsynaptic membrane to the THRESHOLD level and stimulate an AP
• What is summation?


  Summation is where the effect of neurotransmitter released from many neurones (or one neurone which is stimulated a lot in a short period of time)is added together
• What are the two types of summation?


  spatial

  temporal
• Describe spatial summation?


  • sometimes many neurones connected to one neurone
  • the SMALL AMOUNT OF NEUROTRANSMITTER released from EACH of these neurones can be enough altogether to reach the threshold in the postsynaptic neurone and trigger an AP
  • If some neurones release an INHIBITORY neurotransmitter then the TOTAL EFFECT OF ALL neurotransmitters might be NO AP
• Spatial summation?


  many neurones release neurotransmitters = AP

  More inhibitory neurotransmitters are released (-) than excitatory neurotransmitters (+) = NO AP
• What is temporal summation?


  Temporal summation is where 2 or more nerve impulses arrive in QUICK SUCCESSION from the SAME PREsynaptic neurone

  this makes an AP MORE LIKELY because more neurotransmitter is released into the synaptic cleft
• Briefly SUMMMARISE temporal summation?


  high freq of weak impulses = action potential
• Both types of summation mean what?

  Mean synapses accurately process information, finely tuning the response