The Difference Between a Neuron and a Synapse

You Are 86 Billion Cells Talking to Each Other

Right now, as your eyes scan this sentence, something extraordinary is happening inside your skull. Electrical impulses are racing along thin biological fibers at speeds up to 120 meters per second. When each impulse reaches the end of its fiber, it triggers a burst of chemical molecules that float across a gap narrower than a wavelength of visible light. Those molecules land on the next cell, which either fires its own electrical impulse or stays quiet. This decision, fire or don't fire, is happening at roughly 100 trillion junctions in your brain simultaneously.

The cells doing the firing are neurons. The junctions where the decisions get made are synapses.

If you want to understand anything about how the brain works, from why you can't stop checking your phone to how memories form to what consciousness might actually be, you need to understand these two things and the difference between them. Because while people often use "neurons" as shorthand for "brain stuff," the truth is that neurons alone are just a pile of cells. It's the synapses that make them a brain.

The Neuron: Your Brain's Fundamental Unit of Computation

A neuron is a cell. A very weird, very specialized cell, but a cell nonetheless. It has a nucleus, a membrane, mitochondria, all the standard cellular equipment. What makes neurons special is their shape and their obsession with electrical signals.

A typical neuron has three main parts:

The cell body (soma). This is headquarters. It contains the nucleus, handles the cell's metabolic needs, and integrates incoming signals. Think of it as the decision-maker.

Dendrites. These branch out from the cell body like the roots of a tree. Their job is to receive signals from other neurons. A single neuron can have thousands of dendrites, each one listening to a different input. The more dendrites a neuron has, the more information it can take in.

The axon. This is the output cable. It extends from the cell body (sometimes for just a millimeter, sometimes for a meter or more) and carries electrical signals away from the soma toward other neurons. Some axons are wrapped in a fatty insulation called myelin that dramatically speeds up signal transmission, from about 2 meters per second without myelin to 120 meters per second with it.

Here's the crucial point about what neurons do. They compute. Not like a computer chip computes, with binary logic gates, but in a messier, more powerful way. Each neuron receives thousands of inputs through its dendrites. Some of these inputs are excitatory ("fire!") and some are inhibitory ("don't fire!"). The neuron integrates all of these inputs, essentially adding up the excitatory and inhibitory signals. If the sum exceeds a threshold, the neuron fires an electrical impulse called an action potential that travels down its axon. If the sum doesn't reach threshold, nothing happens.

This fire-or-don't-fire decision is called all-or-nothing signaling. There's no half-fire. The action potential either happens or it doesn't. And it always has the same amplitude, about 100 millivolts. The neuron encodes information not by how strongly it fires, but by how frequently it fires and when it fires relative to other neurons.

Think about it this way. Each neuron is receiving potentially 10,000 different opinions (excitatory and inhibitory inputs), weighting them, and producing a single yes-or-no output. It's a tiny voting machine. And your brain has 86 billion of them, all voting simultaneously.

Types of Neurons: Not All Brain Cells Are Created Equal

Neurons come in a surprising variety of shapes and sizes, and the diversity matters.

Pyramidal neurons are the workhorses of the cerebral cortex. They're shaped like triangles (hence the name), with a long apical dendrite pointing toward the brain's surface and a thick axon projecting downward. These are the neurons whose synchronized activity is detected by EEG. They're arranged in parallel, like trees in an orchard, which means their electrical dipoles add up constructively when they fire together.

Purkinje cells in the cerebellum are perhaps the most visually stunning neurons in the brain. Their dendritic trees spread out in enormous, flat fans, like a peacock's tail made of neural wiring. A single Purkinje cell can receive input from over 200,000 other neurons, making it one of the most connected cells in the body.

Interneurons are the brain's local circuit regulators. They're typically small, with short axons that don't leave their immediate neighborhood. Their job is to inhibit nearby neurons, creating the precise timing and rhythm that allows neural circuits to function without dissolving into chaos. Without interneurons, your brain would seize.

Motor neurons extend axons from the spinal cord all the way to muscles, sometimes over a meter long. When you wiggle your toe, a signal travels from your motor cortex down your spinal cord and then along a single motor neuron's axon to the muscles in your foot. One cell, one meter.

The variety is staggering. Researchers have catalogued hundreds of distinct neuron types in the brain, and new ones are still being discovered. But regardless of their shape or location, all neurons share the same fundamental behavior: receive inputs, integrate them, and maybe fire.

The Synapse: Where the Conversation Happens

So neurons fire electrical impulses. But neurons don't touch each other. Between the axon terminal of one neuron and the dendrite of the next, there's a gap. A tiny, fluid-filled space roughly 20-40 nanometers wide. That's about 500 times narrower than the width of a human hair.

This gap is the synaptic cleft, and it's the core of the synapse.

The full synapse consists of three parts:

1. The presynaptic terminal. This is the end of the sending neuron's axon. It contains hundreds of tiny spheres called vesicles, each packed with thousands of neurotransmitter molecules.

2. The synaptic cleft. The gap itself. It's filled with extracellular fluid and a complex scaffold of proteins that help organize the synapse.

3. The postsynaptic membrane. This is the receiving side, part of the next neuron's dendrite (or cell body). It's studded with receptor proteins specifically shaped to bind with the neurotransmitters coming across the cleft.

When an action potential arrives at the presynaptic terminal, here's what happens. And this entire sequence takes about half a millisecond:

The electrical signal triggers voltage-gated calcium channels to open. Calcium ions rush into the terminal. The sudden calcium influx causes vesicles to fuse with the membrane and dump their neurotransmitter cargo into the cleft. The neurotransmitter molecules drift across the gap (this takes only microseconds because the distance is so short). They bind to receptors on the postsynaptic membrane. This binding opens ion channels in the receiving neuron, allowing charged particles to flow in or out, creating a small voltage change called a postsynaptic potential.

If enough excitatory postsynaptic potentials accumulate, the receiving neuron reaches threshold and fires its own action potential. And the whole process repeats at the next synapse.

The "I Had No Idea" Moment: Your Synapses Are Not Fixed. They Change Every Second.

Here's the fact that rewrites how most people think about their brain.

Your synapses are not permanent structures. They're not soldered connections. They're more like volume knobs that get turned up and down based on experience.

When two neurons fire together repeatedly, the synapse between them gets stronger. The presynaptic terminal releases more neurotransmitter. The postsynaptic membrane grows more receptors. The synapse becomes more efficient at transmitting signals. This is called long-term potentiation (LTP), and it was first demonstrated by Terje Lomo in 1966. It's widely believed to be the cellular basis of learning and memory.

The reverse happens too. When neurons stop firing together, their synapse weakens. Fewer vesicles, fewer receptors, weaker transmission. This is long-term depression (LTD), and it's how the brain prunes unused connections.

This constant strengthening and weakening of synapses is called synaptic plasticity, and it's happening in your brain right now, as you read these words. The synapses encoding this information are literally changing their physical structure. Proteins are being synthesized. Receptors are being inserted into membranes. New dendritic spines (tiny bumps on dendrites where synapses form) are growing.

The neuroscientist Donald Hebb summarized this in 1949 with a phrase that became one of the most famous in all of neuroscience: "Neurons that fire together wire together." It's a simplification, but it captures the essence. Your brain's wiring diagram is not a fixed blueprint. It's a living document that gets rewritten by experience, constantly, relentlessly, for your entire life.

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Neurotransmitters: The Chemical Alphabet of the Synapse

The neurotransmitter released at a synapse determines what that synapse does. Different chemicals produce different effects. Here are the ones that matter most:

A crucial distinction: glutamate and GABA are the brain's workhorse neurotransmitters. Together, they account for roughly 90% of all synaptic transmission. Every circuit in your brain, from vision to language to decision-making, runs on the balance between glutamate saying "fire" and GABA saying "don't fire."

Dopamine, serotonin, and norepinephrine are different. They're neuromodulators. Instead of directly triggering or blocking firing, they adjust the sensitivity of entire circuits. Think of glutamate and GABA as the notes in a musical performance, and dopamine and serotonin as the volume and tempo controls. They don't change which notes are playing. They change how the whole piece sounds.

This is why drugs that affect dopamine or serotonin (like SSRIs for depression, or stimulants for ADHD brain patterns) can have such broad effects on mood and cognition. They're not flipping individual switches. They're adjusting the gain on entire brain networks.

Where Neurons and Synapses Meet EEG

Here's where all of this connects to something you can actually observe.

When EEG electrodes sit on your scalp, they don't detect individual neurons firing. They detect what happens at synapses, specifically the postsynaptic potentials generated when large populations of pyramidal neurons receive synaptic input simultaneously.

Think back to the synapse mechanism. When neurotransmitters cross the cleft and open ion channels on the postsynaptic membrane, they create a local voltage change in the receiving neuron's dendrite. This postsynaptic potential lasts tens of milliseconds (much longer than the 1-millisecond action potential) and creates a tiny electrical dipole along the pyramidal neuron's apical dendrite.

Now multiply that by tens of thousands of pyramidal neurons receiving synaptic input at the same time. All those tiny dipoles, oriented in the same direction (because pyramidal neurons are arranged in parallel), add up. The summed electrical field passes through meninges, cerebrospinal fluid, skull, and scalp, and arrives at the EEG electrode as a measurable voltage fluctuation.

So when you see brainwave patterns on an EEG, you're looking at the aggregate of billions of synaptic events. Every wiggle in that waveform reflects neurotransmitters crossing synaptic clefts, ion channels opening and closing, postsynaptic potentials rippling across cortical tissue. The EEG is, in a very literal sense, a readout of your synapses in action.

The Neurosity Crown captures these synaptic echoes from 8 positions across the scalp (CP3, C3, F5, PO3, PO4, F6, C4, CP4), sampling 256 times per second. Each channel is a window into the synchronized synaptic activity of millions of cortical neurons in the region beneath it. The N3 chipset processes these signals on the device itself, extracting frequency band power, signal quality metrics, and cognitive state estimates from the raw synaptic chorus.

Why This Distinction Matters for Understanding Your Brain

The neuron-synapse distinction isn't just academic. It changes how you think about almost everything the brain does.

Learning isn't about growing new neurons (though that does happen in limited brain regions). It's about strengthening and weakening specific synapses, reshaping the connections between existing neurons.

Memory isn't stored in individual neurons like files on a hard drive. It's distributed across patterns of synaptic connections. A memory is a specific constellation of synaptic strengths that, when reactivated, reproduces a particular pattern of neural firing.

Mental illness often involves synaptic dysfunction, not neuron death. Depression is increasingly understood as a disorder of synaptic plasticity, where connections in key circuits (particularly in the prefrontal cortex and hippocampus) weaken excessively. Many antidepressants work by restoring healthy synaptic function.

Aging affects synapses before it affects neurons. Cognitive decline in normal aging correlates more strongly with loss of synaptic density than with neuron loss. Your neurons are remarkably durable. Your synapses are the fragile part.

This reframing is powerful. You are not your neurons. You are the pattern of connections between them. Every experience, every skill, every memory, every personality trait you have is encoded in the specific configuration of your hundred trillion synapses. Change the synapses, and you change the mind.

The Scale That Breaks Your Intuition

Let's put some numbers on this.

Your brain has approximately 86 billion neurons. That's more neurons than stars in the Milky Way galaxy (which has an estimated 100-400 billion, but many of those are dim red dwarfs, so the comparison is closer than it sounds).

Each neuron forms, on average, about 7,000 synaptic connections. Some form 200. Some form 200,000. But the average is roughly 7,000.

Multiply those together and you get approximately 600 trillion synapses (estimates range from 100 to 600 trillion, depending on the methodology and age of the brain). Let's use a conservative estimate of 100 trillion.

One hundred trillion. That's 100,000,000,000,000. If you counted one synapse per second, it would take you about 3.2 million years to count them all. The number of possible patterns of synaptic strengths in your brain is larger than the number of atoms in the observable universe by a factor that itself is incomprehensibly large.

This is what's sitting between your ears. Not a computer. Not a circuit board. Something far more complex, far more dynamic, and far more interesting than anything humans have ever built. And we're only just beginning to read its electrical signature.

The next time someone tells you "neurons fire" as if that explains the brain, you'll know the real story. The neurons fire, sure. But the magic happens at the synapse.