What Are Neurotransmitters? How Brain Cells Communicate

Neurotransmitters are chemical messengers that let neurons talk to each other. They are released by neurons, cross the tiny gaps between cells called synapses, and carry signals to other neurons, to muscles, and to glands. Every thought, movement, memory, emotion, and sensation depends on them. Without neurotransmitters, the brain could not pass information from one neuron to the next.

A message carried across a gap

Neurotransmitters are naturally occurring chemicals made by neurons. Neurons are not physically fused together, so an electrical signal can’t simply flow from one into the next at most synapses. Instead, the sending neuron converts its signal into a chemical message. Think of passing a note across a narrow stream when there’s no bridge: the note is the neurotransmitter, and the person waiting on the other bank is the receptor. The picture is a simplification, since the crossing takes a fraction of a millisecond and many notes are thrown at once, but it captures why chemistry is needed.

The sequence runs in five steps. An action potential, the neuron’s electrical impulse, reaches the axon terminal. Calcium flows into the terminal. Small packets called synaptic vesicles release neurotransmitters into the synaptic cleft. The neurotransmitters bind to receptors on the receiving cell. The receiving cell then responds by changing its electrical activity. Afterward, the neurotransmitters are cleared away by reuptake into cells, by enzymes that break them down, or by diffusing away, which resets the synapse for the next signal. This happens constantly, across vast numbers of synapses throughout the brain.

The major messengers

Several neurotransmitters do much of the brain’s work. Glutamate is the brain’s main excitatory neurotransmitter, making receiving neurons more likely to fire, and it plays an essential role in learning, memory, and synaptic plasticity, the strengthening and weakening of connections. GABA is the main inhibitory neurotransmitter. It reduces excessive neuronal activity and helps keep brain networks balanced.

Dopamine is involved in movement, motivation, learning, reward, and decision-making. Serotonin helps regulate mood, sleep, appetite, digestion, and many other body functions. Acetylcholine is important for muscle contraction, attention, learning, and memory. Norepinephrine helps regulate alertness, attention, and the body’s response to stress.

One messenger, many jobs

It’s tempting to give each neurotransmitter a single label, such as calling dopamine the reward chemical or serotonin the mood chemical. Those labels mislead. Most neurotransmitters have several functions. Dopamine contributes to movement, motivation, learning, and reward. Serotonin influences mood, sleep, digestion, and other processes. What a neurotransmitter does in a given place also depends on the receptors it binds to and on the cell receiving the message.

Why they matter

Neurotransmitters let billions of neurons communicate quickly and efficiently. They make it possible to think, learn, remember, feel emotions, move your muscles, and respond to your surroundings. Normal brain function depends on well-regulated neurotransmitter signaling, meaning the right amount of signal, in the right place, at the right time, rather than any single chemical level being simply too high or too low.

This article is educational background and is not advice about any medication or condition.

Related: What Is a Neuron? · What Is a Synapse? · What Is an Action Potential?

References

1. Caire MJ, Reddy V, Varacallo MA. Physiology, Synapse. StatPearls. Updated March 27, 2023.
2. Cooper GM. Signaling Molecules and Their Receptors. The Cell: A Molecular Approach. NCBI Bookshelf.
3. Grider MH, Jessu R, Kabir R. Physiology, Action Potential. StatPearls. Updated May 8, 2023.