Final answer:
Spatial summation occurs when synaptic potentials that originate in different locations summate within a single neuron to initiate an action potential.
Step-by-step explanation:
Spatial summation refers to the combination of graded potentials from different locations on a neuron, which then summate to initiate an action potential. It occurs when synaptic potentials from separate synapses add up to reach the threshold for firing an action potential. For example, if one synapse produces a small depolarization and another synapse produces a small depolarization at the same time, the combined effect can reach the threshold and trigger an action potential.