Roles of synapses

• What are the roles of synapses?

  • keeps an action potential travelling in one direction
  • filters out background stimuli
• How do synapses keep an action potential travelling in one direction?

  • vesicles containing acetylcholine are only found in the pre-synaptic membrane
  • receptor proteins and Na+ channels are only found on the post-synaptic membrane
• How do synapses filter out background stimuli?

  • not enough Na+ channels open
  • threshold potential isn't met in the post-synaptic neurone
  • there isn't enough depolarisation to stimulate an action potential
• If an action potential from a pre-synaptic neurone isn't sufficient enough to generate an action potential in the post-synaptic neurone, summation (adding neurotransmitters together) can occur
• What are the 2 types of summation?

  • temporal summation
  • spatial summation
• What is temporal summation?

  • where sufficient acetylcholine is released over time
  • requires a high frequency of action potentials in the pre-synaptic neurone
  • otherwise acetylcholine will be hydrolysed in the synaptic cleft by acetylcholinesterase
• What is spatial summation?

  • where there are many pre-synaptic neurones that synapse with one post-synaptic neurone
  • although the amount of acetylcholine released by each pre-synaptic neurone is small and not enough to generate an action potential, the total amount is
• What are the uses of ATP in synaptic transmission?

  • exocytosis
  • reuptake and resynthesis of acetylcholine
  • packaging of acetylcholine into vesicles
  • protein synthesis (ion channels, transport proteins, receptor proteins)
  • active transport of Ca2+ out of the pre-synaptic bulb