Synaptic transmission

• How does synaptic transmission occur?

  1. The arrival of an action potential at the axon terminal causes the voltage gated Ca2+ channels to open. Ca2+ move into the axon terminal by facilitated diffusion.
  2. Synaptic vesicles containing the neurotransmitter acetylcholine move towards and fuse with the pre-synaptic membrane
  3. Acetylcholine is released by exocytosis and it diffuses across the synaptic cleft
  4. Acetylcholine binds to the binding site of a receptor protein on the post-synaptic membrane
• How does synaptic transmission occur 2?

  5. This bind stimulates the opening of Na+ channels, so Na+ moves into the post-synaptic neurone by facilitated diffusion.

  6.If threshold is achieved (as sufficient Na+ enters), an action potential will be generated in the post-synaptic neurone

  7. Acetylcholine is broken down by acetylcholinesterase by hydrolysis, so it changes shape and can no longer bind to the receptor proteins
• How does synaptic transmission occur 3?

  8. Na+ channels close

  9. There is reuptake of acetyl and choline into the synaptic bulb. Acetylcholine is resynthesised and repackaged into vesicles. All of this requires ATP.
• Label this diagram of a synapse

  A) pre-synaptic neurone

  B) synaptic bulb

  C) synaptic cleft/space

  D) post-synaptic neurone

  E) Ca2+ channel

  F) synaptic vesicle containing acetylcholine

  G) pre-synaptic membrane

  H) post-synaptic membrane

  I) protein receptor

  J) ion channel