Features of Synapses (A-level Biology)

Features of Synapses

Synapse Features

Synapses have three distinct features:

  • Unidirectionality
  • Inhibition by inhibitory synapses
  • Temporal and spatial summation

We have already explored the first two bullet points, so now we will look at summation.


  • An action potential can only be initiated when the depolarisation is large enough to reach the threshold. If an impulse is too weak, not enough neurotransmitters will be released across a synapse to trigger this.
  • An impulse can be built up by summation, where the effects of neurotransmitters are combined. This allows the synapses to more accurately process information.

There are two types of summation:

      • Temporal summation – Where multiple nerve impulses from a single pre-synaptic neurone occur in succession. This increases the concentration of neurotransmitters in the synaptic cleft, increasing the likelihood of firing an action potential.
      • Spatial summation – Where multiple pre-synaptic neurones connect to the same post-synaptic neurone. The combination of both inhibitory and excitatory neurones are ‘added together’ to determine if an action potential will fire.

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