SPATIAL AND TEMPORAL SUMMATION
Neurons receive multiple excitatory and inhibitory inputs.
C, Temporal summation occurs when a series of subthreshold EPSPs in one excitatory fiber produce an AP in the postsynaptic cell. This occurs because the EPSPs are superimposed on each other temporally before the local region of membrane has completely returned to its resting state.
D, Spatial summation occurs when subthreshold impulses from two or more synapses trigger an AP because of synergistic interactions. E, Both temporal and spatial summation can be modulated by simultaneous inhibitory input. Inhibitory and excitatory neurons use a wide variety of neurotransmitters, whose actions depend on the ion channels opened by the ligandreceptor interactions.