What is the name for the chemicals stored in the synaptic vesicles?

Neurotransmitters.

Within a neuron, there are long tubes known as Neurotubules. These carry the synaptic vesicles from the cell body to the synapse (like a factory conveyor belt). When an electrical impulse arrives at the neuron's synapse, the synaptic vesicle fuses with the cell membrane and releases lots of molecules known as Neurotransmitters .

These neurotransmitters are responsible for turning the electrical impulse into a chemical one, which crosses over to the next neuron to become an electrical one again (and thus the signal is passed on).

(If you want to learn more about this, then click to go to my answer on synapses and impulses)

Hope this helped! Let me know if I can do anything else for you:)