What are neurotransmitters?

Neurotransmitters are chemicals used to transmit signals between neurons. (Makes sense, doesn’t it?) They’re emitted from the axon of the sender, cross the synapse to the receiver, and attach to a receptor site on a dendrite there. If the receiver is properly excited by the intrusion, it sends its own neurotransmitters to its neighbors; and so on. In this way, long concatenations of impulses are sent coursing through you, and you yelp when you stab your finger with the needle. Again.

Some gripping examples of neurotransmitters are dopamine, serotonin, and norepinephrine. You really should look them up.