The Synapse

• • once the action potential has been propagated along the axon via continuous or saltatory conduction, it reaches the terminal button
  • here the membrane contains a different type of voltage gated channels, they dont permit the flow of potassium and sodium, they permit the flow of calcium ions (Ca2+)
  • depolarisation allows the channels to be opening, allowing the flow of calcium, which follows its diffusion force and electrostatic pressure to flow inwards into the membrane

  
• • every time an action potential reaches the terminal button, voltage gated channels will open and there will be an influx of calcium
  • a high frequency of action potentials arriving at the terminal button means theres a high frequency of calcium flowing into the membrane
  • the influx of calcium triggers the process where the vesicles containing the neurotransmitter, bind with the membrane, releasing the neurotransmitter into the synaptic cleft

  
• • once the neurotransmitters have crossed the synaptic cleft, the bind with the chemically gated channels, causing postsynaptic potentials - can be excitatory postsynaptic potentials or inhibitory postsynaptic potentials
  • a short while after the neurotransmitter is released and binds with the channels, enzymes are released into the synaptic cleft to break the neurotransmitter down - time limited event

  
• After neurotransmitters are released into the synaptic cleft, there can be:

  1. reuptake of neurotransmitters back into the synaptic button or
  2. enzymes are released into the synaptic cleft to break the neurotransmitters down