Probably activates microtubules which force movement of vesicles. After considerable use, the vesicles are transported back to the cell for repair. The excess membrane is removed at the axon-buton junction. Both decline with distance and time. Since they decline, the closer they are to the axon hillock the greater their effect.
Most inhibitatory synapses are on the cell body thus have greater effect.
Temporal Summation refers to the combined effects of neurotransmitter release from the same sites over time. Hormones - stimulate the postsynaptic membranes of specific target cells. Neuromodulators - influencet the amount of neurotransmitter released but do not act directly on postsynaptic membranes like hormones. Endorphins - example of a neuromodulator.