Final answer:
Spatial summation refers to multiple signals from different presynaptic neurons converging on a single postsynaptic neuron, with the combined effect influencing whether an action potential is generated. These signals can arrive at slightly different times. the correct option is (a).
Step-by-step explanation:
Which of the following is true of spatial summation? The correct answer is: neurotransmitters released simultaneously from several presynaptic knobs converge on one postsynaptic neuron. Spatial summation involves multiple signals from various presynaptic neurons converging and adding together at a single postsynaptic neuron. These signals can be excitatory postsynaptic potentials (EPSPs) or inhibitory postsynaptic potentials (IPSPs), and the net effect of all these signals determines whether the postsynaptic neuron reaches the threshold to fire an action potential. Spatial summation does not have to occur simultaneously; signals can arrive on the postsynaptic neuron at slightly different times and still be effective. This differs from temporal summation, where repetitive signals come from the same neuron but separated in time.