Final answer:
Temporal summation refers to a presynaptic neuron sending frequent excitatory postsynaptic potentials in quick succession, which can cumulatively depolarize the postsynaptic neuron to threshold, triggering an action potential.
Step-by-step explanation:
If a postsynaptic cell is stimulated to threshold by temporal summation, this implies that a presynaptic neuron is sending frequent EPSPs (excitatory postsynaptic potentials). Temporal summation is the process where multiple EPSPs are generated in quick succession by one or more presynaptic neurons, leading to a cumulative effect that can bring the postsynaptic membrane potential to the threshold needed for an action potential. It does not necessarily relate to the frequency of action potentials being sent by the postsynaptic cell itself, nor the number of presynaptic cells involved.
Spatial summation, on the other hand, involves the combination of EPSPs from multiple presynaptic neurons at different locations on the postsynaptic neuron's membrane. In contrast, temporal summation refers to the timing and rapid succession of EPSPs at the same location. When sufficient EPSPs occur in such a manner that their combined effect reaches the threshold, an action potential is triggered in the postsynaptic neuron.