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.
