Identifying a Neurotransmitter

How they work, different types, and why they're important

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A neurotransmitter is a chemical messenger that carries, boosts, and balances signals between neurons, or nerve cells, and other cells in the body. Billions of neurotransmitters work constantly to keep our brains functioning, managing everything from our breathing to our heartbeat to our learning and concentration levels. 

How Neurotransmitters Work

In most cases, a neurotransmitter is released from what's known as the axon terminal after an action potential has reached the synapse, a place where neurons can transmit signals to each other.

After release, the neurotransmitter crosses the synaptic gap and attaches to the receptor site on the other neuron, either exciting or inhibiting the receiving neuron depending on what the neurotransmitter is.  Once the neurotransmitter has had the designed effect, its activity can be stopped by different mechanisms. It can be degraded or deactivated by enzymes, it can drift away from the receptor, or the neurotransmitter can be taken back up by the axon of the neuron that released it in a process know as reuptake.

Neurotransmitters play a major role in everyday life and functioning. Scientists do not yet know exactly how many neurotransmitters exist, but more than 100 chemical messengers have been identified.

When neurotransmitters are affected by disease or drugs, there can be a number of different adverse effects on the body. Diseases such as Alzheimer's, epilepsy, and Parkinson's are associated with deficits in certain neurotransmitters.

What Neurotransmitters Do

Neurotransmitters can be classified by their function:

  • Excitatory neurotransmitters: These types of neurotransmitters have excitatory effects on the neuron, meaning they increase the likelihood that the neuron will fire an action potential. Some of the major excitatory neurotransmitters include epinephrine and norepinephrine.
  • Inhibitory neurotransmitters: These types of neurotransmitters have inhibitory effects on the neuron; they decrease the likelihood that the neuron will fire an action potential. Some of the major inhibitory neurotransmitters include serotonin and gamma-aminobutyric acid (GABA).

Some neurotransmitters, such as acetylcholine and dopamine, can create both excitatory and inhibitory effects depending upon the type of receptors that are present.

Neurotransmitter Types

Neurotransmitters can also be categorized into one of six types:

  1. Acetylcholine
  2. Amino acids: Gamma-aminobutyric acid (GABA) and glycine glutamate aspartate
  3. Neuropeptides: Oxytocin, endorphins, vasopressin, etc
  4. Monoamines: Epinephrine, norepinephrine, histamine, dopamine, and serotonin
  5. Purines: Adenosine, adenosine triphosphate (ATP) 
  6. Lipids and gasses: Nitric oxide, cannabinoids

Identifying Neurotransmitters

The actual identification of neurotransmitters can actually be quite difficult. While scientists can observe the vesicles containing neurotransmitters, figuring out what chemicals are stored in the vesicles is not quite so simple.

Because of this, neuroscientists have developed a number of guidelines for determining whether or not a chemical should be called a neurotransmitter:

  1. The chemical must be produced inside the neuron.
  2. The necessary precursor enzymes must be present in the neuron.
  3. There must be enough of the chemical present to actually have an effect on the postsynaptic neuron.
  4. The chemical must be released by the presynaptic neuron, and the postsynaptic neuron must contain receptors that the chemical will bind to.
  5. There must be a reuptake mechanism or enzyme present that stops the action of the chemical.


Chudler, EH. Neurotransmitters and Neuroactive Peptides. Neuroscience for Kids.

Perry, S. Neurotransmitters: How Brain Cells Use Chemicals to Communicate. May 16, 2011.

Thompson, RF. The Brain: A Neuroscience Primer. New York: Worth Publishers; 2000.