Final answer:
Spatial summation involves the combination of multiple graded potentials from different locations on a neuron, while temporal summation involves graded potentials that occur at the same location but at different times, both potentially leading to an action potential.
Step-by-step explanation:
Spatial and temporal summation are both mechanisms by which neurons integrate signals, but they function in different ways. Spatial summation occurs when multiple graded potentials from various locations on a neuron combine at the axon hillock, potentially leading to an action potential if the threshold is reached. Contrarily, temporal summation refers to the combination of several graded potentials at the same location on a neuron but occurring at different times, amplifying the signal strength.
Spatial summation can involve signals arriving at slightly different times, as long as they overlap sufficiently to be summed. Temporal summation, however, precisely relies on the timing of graded potentials to cause a significant change in the membrane potential. Summation typically occurs in the axon hillock or the initial segment of the axon, where there is a high density of voltage-gated Na+ channels that can initiate an action potential.