Final answer:
Excitatory postsynaptic potentials involve the opening of chemically gated cation channels and inflow of sodium leading to depolarization of the postsynaptic neuron. This current strengthens as it moves toward the axon hillock, and an increased binding of neurotransmitter to cation channels results in stronger depolarization.
Step-by-step explanation:
The true statements of excitatory postsynaptic potentials (EPSPs) are as follows:
a. Chemically gated cation channels open and let sodium in and potassium out. When neurotransmitters like acetylcholine bind to receptors at the neuromuscular junction, they cause the postsynaptic Na+ channels to open, permitting the inflow of Na+ ions and leading to depolarization.
b. The postsynaptic neuron depolarizes, because the Na+ entering the cell reduces the voltage across the postsynaptic membrane.
c. The local sodium current becomes stronger as it moves toward the axon hillock, where the aggregation of depolarization can potentially trigger an action potential if the threshold is reached.
d. More neurotransmitter bound to cation channels will result in a stronger depolarization, due to the increased influx of positive ions raising the internal membrane voltage closer to the action potential threshold.