I imagine neurotransmitters as the grease that keeps the brain functioning much the same way that a well-oiled machine runs smoothly. Without neurotransmitters, communication between neurons does not happen. It is the neurotransmitters that carry nerve impulses across synapses from one neuron to the next.
When a neuron initially fires, it sends an electrical signal down its axon to the pre-synaptic terminal (also known as the end of the neuron and the end of the axon). The neurotransmitter’s task is to convert that electrical signal to a chemical signal and transmit it across the synapse to the dendrites of a nearby neuron. The nearby neuron’s dendrites contain receptors to receive that transmission, which convert the chemical signal into a new electrical signal.
For a visual explanation of how this process works visit the Mind Project’s Flash animation Introduction to Synapses. A consortium of educational institutions, the folks at The Mind Project are creating “curriculum materials that provide students with a challenging yet accessible introduction to the cognitive sciences (the study of the mind and brain).”
Back in 1921, Otto Loewi discovered the first neurotransmitter, Acetylcholine, and there are now some 50 or so known neurotransmitters. Over the next several posts we will explore some of the ones that just roll off the tongue (!): Acetylcholine, Dopamine, Epinephrine, Endorphin, Norepinephrine, Serotonin, Cortisol and Melatonin. Meanwhile you can check out some neurotransmitter tidbits at Neuroscience for Kids – Neurotransmitters.