Final answer:
The assertion that spatial summation occurs when multiple graded potentials from different synapses on the same neuron combine is true. Spatial summation contributes to reaching the threshold potential necessary for an action potential. The correct option is A.
Step-by-step explanation:
The statement that two or more graded potentials originating from different synapses on the same neuron at approximately the same time will cause spatial summation is true. Spatial summation refers to the combination of graded potentials across the neuronal cell membrane caused by signals from separate presynaptic elements that add together to initiate an action potential.
This process is distinct from temporal summation, which involves the combination of graded potentials at the same location on a neuron over a period of time resulting in a strong signal from one input.
Spatial and temporal summation can work in concert, leading to the membrane reaching threshold and potentially triggering an action potential.
Specifically, in spatial summation, excitatory postsynaptic potentials (EPSPs) from various synapses accumulate, potentially causing a large enough overall depolarization to bring the neuron's membrane potential to threshold, thereby initiating an action potential.