Before tackling the main neurotransmitters and their functions, let’s review how neurons – the specialized cells of the nervous systems – work. Neurons are electrically excitable, and relay information by changing their concentrations of charged ions in a process called action potential. An action potential will eventually travel down the axon, a tube-like projection that links neurons to other cells and each other at a synapse. At the end of the axon, neurotransmitters are released into a space between the excited neuron and another neuron or cell. By binding to specific receptors, neurotransmitters can excite, inhibit, or otherwise change a cell; in turn, these cellular changes can have some big affects on the whole organism.
Let’s start with one of the best-known neurotransmitters: serotonin. Serotonin is famously implicated in modulating mood, sleep, and motivation; people with decreased serotonin levels or function can suffer from depression. Likewise, increased levels of serotonin are suspected to cause decreased cognitive functions and perhaps autism. Though serotonin is most often thought of as a mood-mediating neurotransmitter, the majority of the body’s supply works to regulate intestinal movements.
Glutamate is the most common excitatory neurotransmitter (it passes action potential from one neuron to another). Glutamate is involved in long-term potentiation, a process that strengthens synapses. This strengthening ability makes glutamate key in learning and memory.
Conversely, GABA is the main inhibitory neurotransmitter that dulls down excitement by preventing action potential in the neurons it affects. Although inhibitory in adults, GABA is primarily excitatory in early development and regulates the growth of embryonic and neuronal stem cells as they grow into neurons and form synapses.
Although it has some functions in the brain, acetylcholine mainly works in the peripheral nervous system, by contracting the muscles that make us run, jump, and generally move around.
Next up, norepinephrine and epinephrine (noradrenaline and adrenaline) are stress hormones that mediate the fight-or-flight response, which increases heart rate, blood flow, and available glucose when an individual is threatened. Surplus levels of these neurotransmitters might cause anxiety disorders and panic symptoms. Endorphins similarly kick in during excitement, numbing pain and creating a feeling of well being during physically and emotionally intense moments like exercise, sex, and pregnancy and childbirth.
Dopamine is another excitatory neurotransmitter involved in a wide range of functions: from learning and memory to muscle movement. It’s thought that dopamine is key in reward pathways that mediate pleasure seeking behaviors and addiction. Dopamine dysfunctions may cause perceptual disorders, hallucinations, and schizophrenia.
Though neurotransmitter might be small, they’re clearly responsible for some very big things. After considering these tiny chemical signals and all that they can do - whether you’re a neuron or a person, it's clear that a little communication goes a long way.