Transmission across a Cholinergic Synapse

• There are over 40 different known neurotransmitters
• Acetylcholine (ACh)


  One of the key neurotransmitters used throughout the nervous system
• Cholinergic synapses


  Synapses that use the neurotransmitter ACh
• Synaptic transmission using ACh

  1. Action potential arrives, depolarising presynaptic membrane

  2. Calcium ion channel proteins open, calcium ions diffuse in

  3. Presynaptic vesicles fuse with membrane, ACh released

  4. ACh diffuses across synaptic cleft

  5. ACh binds to receptor proteins, receptor proteins open, sodium ions diffuse through

  6. Postsynaptic membrane is depolarised

  7. ACh broken down into acetate and choline by acetylcholinesterase, choline recycled into ACh
• Synapses


  • Unidirectionality - Impulses can only pass in one direction
  • Summation - Effect of multiple impulses can be added together
• Temporal summation


  Multiple impulses arrive within quick succession, effect of impulses added together to generate action potential
• Spatial summation


  Multiple impulses arriving simultaneously at different synaptic knobs stimulating same cell body, generate action potential
• Excitatory neurotransmitters


  Can stimulate generation of action potential in postsynaptic neurone by opening sodium ion channels
• Inhibitory neurotransmitters


  Can prevent generation of action potential in postsynaptic neurone by opening potassium ion channels
• Neurone subject to both excitatory and inhibitory synapses

  Sodium ions enter cell body following excitatory synapse, potassium ions diffuse out following inhibitory synapse, cancelling each other out so threshold not reached and no action potential generated