Final answer:
Spatial summation is the process by which multiple inputs on a neuron combine their effects to reach the threshold level of depolarization necessary for an action potential to be fired. This can happen when the same stimulus is repeated until the threshold level is reached.
Step-by-step explanation:
Summation is the process by which multiple graded potentials are added together to reach the threshold level of depolarization necessary for an action potential to be fired in a neuron. In spatial summation, the same stimulus is repeated until the threshold level of depolarization is reached. This can happen when multiple inputs from different locations on the neuron combine their effects to reach the threshold. Spatial summation can also occur when multiple inputs arrive at the same location on the neuron but are separated in time.