Summation combines excitatory and inhibitory postsynaptic effects, determining whether the postsynaptic neuron reaches threshold and fires, linking cellular mechanisms to rapid communication in nervous systems.
Coverage 2018–2018 · Updated 15 Jul 2026
Summation combines graded postsynaptic potentials across space and time at the axon hillock.
Spatial summation adds inputs from different synapses; temporal summation adds repeated inputs from one synapse. The net potential reaches threshold only if excitation outweighs inhibition. The result depends on timing as well as size, because inputs that overlap can combine before the threshold decision.
Separate the two forms:
Two small EPSPs arriving together at the axon hillock can reach threshold even though neither would trigger an action potential alone.
The neuron integrates potentials, not neurotransmitter names; receptor effects determine the sign and size.
This objective is assessed through structured response, commonly using Explain.
Explain
Build the answer around this relationship: Summation combines postsynaptic effects from multiple presynaptic neurons.
Representative question
Explain the effect of the interaction between the activities of excitatory and inhibitory presynaptic neurons at synapses on the central nervous system.
