BY4.7 Synapses

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  • neurones are not in direct contact with one another
  • they are separated by gaps called synapses
  • the main role of the synapses is to convey action potentials between neurones

structure of a synapse

  • most junctions between neurones take the role of chemical synapses
  • branches of axons lie in close contact to dendrites of another neurone but don't touch
  • there is a gap of 20nanometres
  • impulse is transmitted by the secretion of neurotransmitters from he presynaptic membranes to diffuse into the post synaptic membrane

synaptic transmission:

  • nerve impulse (action potential) arrives at the presynaptic membrane
  • voltage gated calcium channels on the presynaptic membrane open
  • calcium dffuses in down a concentration gradient
  • vesicles fuse to the membrane and burst
  • neurotransmitters (acetylcholine…


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