Temporal and spatial summation

EPSP and IPSP

  • A PSP is a post-synaptic potential.  This is the potential generated by activation of a single synapse.  This can be
    • Excitatory (EPSP)- usually depolarises the post-synaptic cell
    • Inhibitory (IPSP)- usually hyperpolarises the post-synaptic cell
  • NB Rarely will a single EPSP generate a post-synaptic action potention.  More than one is usually needed.  They can be combined in one of two ways:

Temporal summation

  • In response to a graded potential, the membrane potential takes time to return to its normal resting state.
  • If one excitatory input depolarise the cell in quick succession, the graded potentials can effectively ‘piggy-back’ on one another, adding up their effect.

Spatial summation

  • This is when more than one excitatory input stimulates the post-synaptic cell simultaneously, adding their effect to one another.
It's not a very good picture, but it demonstrates it when you look into it.
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