Final answer:
The relationship between postsynaptic membrane potential and EPC amplitude is a direct correlation, with an increase in EPC amplitude leading to a more depolarized membrane potential, potentially triggering an action potential if a certain threshold is met.
Step-by-step explanation:
The relationship between postsynaptic membrane potential and the EPC amplitude is a direct correlation. This means that as the amplitude of the excitatory postsynaptic current (EPC) increases, there is a corresponding increase in the depolarization and, thus, the membrane potential of the postsynaptic neuron.
In physiological terms, the greater the influx of positive ions through postsynaptic receptors (e.g., due to a larger excitatory presynaptic input), the more positive the postsynaptic membrane becomes. This change is reflected by an increase in EPC amplitude, which mirrors a rise in the membrane potential. If the membrane potential reaches a certain threshold, it can trigger an action potential, which is a rapid up-and-down shift in membrane voltage that constitutes a fundamental signal in neural communication.