Neurotransmitters: The Brain's Chemical Messengers

Every second, billions of messages race through your brain. They help you move your muscles, remember a name, laugh at a joke, and even blink without thinking. But those messages face an unexpected obstacle: the neurons sending them almost never actually touch.

So how does one neuron communicate with the next?

The answer lies in tiny chemical messengers called neurotransmitters.

In the previous article, we explored how neurons communicate by passing signals across synapses. In this article, we'll take a closer look at the molecules that make that communication possible, how they allow neurons to "talk" to one another, and why different neurotransmitters influence everything from movement and memory to mood and sleep.

What Is a Neurotransmitter?

A neurotransmitter is a chemical messenger released by a neuron in order to communicate with the next cell in line. When an electrical signal reaches the end of a neuron, it triggers the release of neurotransmitters, which cross the tiny gap of the synapse and bind to receptors on the next neuron. That binding is what allows the message to continue traveling through the brain's communication network.

This chemical step exists because of a simple physical limitation: neurons aren't actually connected to one another. An electrical signal can travel efficiently within a single neuron, but it can't leap across the gap of a synapse on its own. Neurotransmitters solve that problem by converting the message into a form that can physically cross the gap, where it's then converted back into an electrical signal inside the next neuron.

Neurotransmitters don't create thoughts or emotions by themselves—they simply allow neurons to pass information through the brain's communication network.

How Do Neurotransmitters Work?

No matter which neurotransmitter is involved, the communication process follows the same basic sequence.

An electrical signal, called an action potential, reaches the axon terminal at the end of a neuron. That arrival triggers the release of neurotransmitters into the synapse. The neurotransmitters cross that small gap and bind to receptors on the next neuron. Once bound, they cause the next neuron to receive the message, and communication continues on to whatever comes next in the pathway.

This sequence happens over and over, at trillions of synapses, every second—an electrical signal converted to a chemical one, crossing a gap, and converting back to an electrical signal on the other side. The entire exchange takes a fraction of a second, which is part of why communication throughout the brain feels instantaneous even though it depends on this chemical relay at every single connection point.

Not All Neurotransmitters Do the Same Thing

Not every neurotransmitter has the same effect once it reaches the next neuron. Some neurotransmitters are excitatory, meaning they increase the likelihood that the next neuron will send a signal of its own. Others are inhibitory, meaning they decrease that likelihood, effectively calming activity down rather than encouraging it.

Beyond this basic distinction, different neurotransmitters also help regulate different functions throughout the brain and body—everything from movement and mood to memory and alertness depends on specific neurotransmitters doing their particular job. A single neuron might release the same neurotransmitter at every one of its synapses, but the effect that neurotransmitter has can still vary depending on which receptors are present on the receiving neuron, since the same chemical message can be interpreted differently depending on where it lands.

Scientists have identified many neurotransmitters, but a handful are responsible for some of the brain's most important everyday functions.

Five Important Neurotransmitters

Dopamine plays a central role in movement, motivation, reward, and learning.

Serotonin helps regulate mood, sleep, and appetite.

Glutamate is the most common excitatory neurotransmitter in the brain, closely tied to learning and memory.

GABA is the most common inhibitory neurotransmitter in the brain. It helps prevent excessive brain activity and keeps neural communication balanced.

Acetylcholine is involved in muscle movement, attention, learning, and memory.

What Happens When Neurotransmitter Communication Changes?

Neurotransmitter communication can be disrupted in a few different ways: neurotransmitters may not be produced normally, may not be released properly, or may not be received effectively by the next neuron.

Conditions like Parkinson's disease, depression, Alzheimer's disease, and epilepsy have all been linked, in different ways, to changes in neurotransmitter communication. Parkinson's disease, for example, involves the loss of neurons that produce dopamine. Depression has long been associated with changes in serotonin signaling, though researchers now understand the picture to be more complex than a single chemical being simply "too low." Alzheimer's disease involves disruption to acetylcholine-using neurons, among other changes. Epilepsy can involve an imbalance between excitatory and inhibitory signaling, tipping the brain's activity out of balance.

Although many neurological conditions involve neurotransmitters, they are rarely caused by changes in just one chemical. Instead, they usually involve complex changes throughout the brain's communication network.