Final answer:
Summation is the phenomenon where a neuron receives both excitatory and inhibitory signals from multiple sources, which combine at the axon hillock. An action potential is fired if the combined excitatory postsynaptic potentials exceed inhibitory inputs and reach the excitation threshold.
Step-by-step explanation:
The phenomenon where signals from multiple neuron sources can terminate on a single neuron sending both excitatory and inhibitory signals is known as summation. This involves the integration of excitatory postsynaptic potentials (EPSPs), which result in local membrane depolarization, and inhibitory postsynaptic potentials (IPSPs), which result in hyperpolarization. These signals are added together at the neuron's axon hillock. If the combined EPSPs are sufficient to overcome any IPSPs and reach the threshold of excitation, then the neuron will initiate an action potential .Two types of summation can occur: spatial summation, which is the combination of graded potentials across the neuronal cell membrane from separate presynaptic elements, and temporal summation, which is the combination of graded potentials at the same location on a neuron over time, resulting in a strong signal from one input. Summation acts as a filter to prevent random electrical noise from being transmitted as important information.