In the case of two EPSPs occurring at a single synapse, which of the following will produce a subthreshold effect and not generate an action potential on the postsynaptic neuron’s axon hillock? a. Both EPSPs occurring in rapid succession
b. The summed EPSPs depolarizing the axon hillock membrane to —70 mV
c. Both EPSPs occurring before the postsynaptic membrane potential returns to —55 mV
d. Both potentials occurring after the postsynaptic membrane potential returns to its resting value

Both potentials occurring after the postsynaptic membrane potential returns to its resting value

Explanation:

This is simply because, a neuron returning to its resting state,will have the ligand gated Na+ channels closed.Therefore depolarization can not occur.More K+ gated channels will open, and more K+ leaks out of the axoplasm,returning the neuron to the resting state.

Hence if  the summation of the two EPSP returns to the resting level after crossing the synapse, they can not propagate,and generate action potential, because they will produce  a sub threshold effects,which  will not generate action potential.

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