Synapses

• What are synapses?

  Gaps between nerve cells
• Why can't action potentials pass across synapses?

  Because they require transmitter substances
• What is the structure of a synapse?

  • Junction between two neurones
  • Presynaptic membrane releases neurotransmitters
  • Postsynaptic cell receives impulses
• What do synaptic vesicles contain?

  Neurotransmitter
• What happens when an action potential arrives at a synapse?

  The membrane depolarises and calcium channels open
• What role do calcium ions play in synaptic transmission?

  They cause synaptic vesicles to fuse with the membrane
• What is released into the synaptic cleft?

  Neurotransmitter
• What happens when neurotransmitter binds to receptors on the postsynaptic membrane?

  Sodium channels open and sodium ions flow in
• What initiates an action potential in the postsynaptic cell?

  Depolarisation of the membrane
• What happens to the neurotransmitter after it binds to receptors?

  It is taken up or broken down
• What was the first neurotransmitter to be discovered?

  Acetylcholine
• What is one function of acetylcholine?

  Stimulation of muscles
• Where is acetylcholine largely made?

  In the brain
• How is acetylcholine broken down in the synaptic cleft?

  By acetylcholinesterase
• What effect does botulism toxin have on acetylcholine release?

  It prevents the release of acetylcholine
• What is the consequence of botulism toxin on respiratory muscles?

  It causes paralysis and suffocation
• What are the steps of neurotransmitter release at a synapse?

  1. Action potential arrives
  2. Membrane depolarises; calcium channels open
  3. Calcium ions enter axoplasm
  4. Synaptic vesicles fuse with presynaptic membrane
  5. Neurotransmitter released into synaptic cleft
  6. Neurotransmitter binds to receptors; sodium channels open
  7. Membrane depolarises; action potential initiated
  8. Neurotransmitter uptake or breakdown occurs