synapses

• what happens at a synapse 1

  1. action potential arrives
  2. voltage gated calcium ion channels open
  3. vesicles containing acetylcholine move to presynaptic membrane - calcium ions fuse with the vesicles and cause them to move to the membrane
  4. vesicles fuse with the presynaptic membrane and release acetylcholine into the synaptic cleft
• what happens at a synapse 2

  1. acetylcholine diffuses across the synaptic cleft to the postsynaptic membrane
  2. acetylcholine binds to receptors in postsynaptic membrane
  3. sodium ion channels open - the membrane is depolarised and an action potential is produced - sodium channels there are ligand gated channels as they only open in response to ligand/ chemical messenger. They are acetylcholine (ACh) receptors
• last step

  • acetylcholine broken down into choline and acetic acid/ ethanoic acid by the enzyme acetylcholinesterase (AChE).
  • This enzyme is found in the synaptic cleft.
  • These products diffuse back into the synaptic bulb where ATP is used to re-combine them and make acetylcholine.