A class of chemical called a neurotransmitter is important in the transmission of nerve impulses. Neurotransmitters are packaged by the cell into small, membrane-bound sacs called vesicles. Upon receiving a chemical signal, the vesicles move toward the plasma membrane and fuse with it, releasing the enclosed neurotransmitters from the terminal end of the nerve cell. Which organelle is most likely responsible for packing neurotransmitters into a vesicle?