Synapses

• describe the structure of a synapse?

  • Synaptic cleft
  • presynaptic neurone
  • Postsynaptic neurone
  • Synaptic knob
  • Synaptic vesicle
  • Neurotransmitter receptors
• what’s the postsynaptic neurone?


  the neurone that receives the neurotransmitters
• what does the synaptic knob contain


  large amounts of mitochondria, endoplasmic reticulum to enable it to manufacture the neurotransmitters through the vesicles
• what are contained in the synaptic vesicles?

  the neurotransmitters
• what do synaptic vesicles do?


  they fuse with the presynaptic membrane and release their contents into the synaptic cleft
• what are neurotransmitter receptors?


  receptor molecule which they bind to on the post synaptic membrane
• name the two types of neurotransmitter

  • excitatory
  • inhibitory
• name an example of an excitatory neurotransmitters 


  Acetylcholine
• describe what an excitatory neurotransmitter is


  they result in the depolarisation of the postsynaptic neurone, only if threshold value is reached an action potential is triggered in the postsynaptic membrane
• describe what an inhibitory neurotransmitter is


  result in the hyper-polarisation of the postsynaptic membrane , preventing an action potential.
• give an example of an inhibitory neurotransmitter

  GABA (Gamma-aminobutyric acid) found in some synapses in the brain
• describe the events of synaptic transmission p1

  • the action potential reaches the end of a pre synaptic neurone
  • depolarisation of the presynaptic membrane causes Calcium ion channels to open
  • Calcium ions diffuse into the pre synaptic knob
  • causing the synaptic vesicles (with NT) to fuse with presynaptic membrane, released into the synaptic cleft by exocytosis
• describe the events in transmission of impulses across a synapse p2

  • neurotransmitter diffuses across the cleft, binds too specific receptor molecule on post synaptic membrane
  • causing sodium ion channels to open
  • they diffuse into the postsynaptic neurone
  • this triggers an action potential, impulse propagated along the postsynaptic neurone