Neurons, or nerve cells, do not touch one another; they are separated by gaps known as synapses. Therefore,  without  serotonin, dopamine, norepinefrine and hundreds of other neurotransmitters, the brain could not process information or send out instructions to run the rest of the body. When the electrical impulses that carry information though the nervous system reach the end of the neuron, they have nowhere to go. These chemicals are stores in tiny sacs known as vesicles, located at nerve endings. When an electrical signal reaches the vesicles, they release their load. The neurotransmitter molecules navigate across the synapse and lock into receptors on the neighboring nerve cell. The second nerve cell wakes up an sends off a jolt of electricity to pass the message along. Teir job completed, the neurotransmitter molecules detach and are ferried back to be reabsorbed or destroyed. Different neurons specialize in releasing different neurotransmitter. Many carry messages that convey facts about the outside world - incoming sounds, patterns of light and so on - and integrate them into useful information. See more on neurotransmitters in Brain & Mind: Communication Between Nerve Cells Photo by André Malavazzi