The Science Of Depression (Briefly Explained)

Special thanks to Dr. Jens Foell for fact-checking this article. Featured artwork of a gold leaf brain by Greg Dunn.

It’s important for you to know how your brain works.

At the very least, you should understand the basics of neural functioning. Your brain is among the most complex and beautiful structures in the known Universe, so you’d be missing out if you never learned a little bit about how it works.

However, books about neuroscience can be confusing and hard to follow if you don’t have a background in biology. So, in layman’s terms, here’s a general explanation of how your brain functions – and what might be happening when things go wrong.

You have, give or take, 86 billion neurons, which are an important type of brain cell. (For the sake of simplicity, let’s just refer to them as cells.) On average, each of those cells communicates with thousands of other cells, which means you have at least 100 trillion connections in that squishy, three-pound meat computer in your head. The site of each of these connections, which is a very small space between cells called a synapse [SIN-apps], is where the magic happens.

An illustration of two brain cells that can communicate with each other. Notice how tiny a synapse is.

But before we look at why synapses are important, we have to know more about how the cells themselves work. Basically, they’re powered by electricity. The wall of a brain cell allows specific electrically charged atoms to move in and out of the cell’s body. This happens in short bursts, each of which creates an electrical charge.

That electrical charge moves very, very quickly away from the body of the cell and through the cell’s long arm, called an axon [AXE-on]. When the charge reaches the end of the axon, it opens up a channel where nanoscopic (smaller than microscopic!) chemicals called neurotransmitters can flow out of their holding area in tip of the cell and into the synapse. (Remember, the synapse is the space between two cells.)

A close-up on the synapse. The first brain cell (right) is sending neurotransmitters, shown as small circles, to the second cell (left). You have trillions of these synapses in your brain.

Once neurotransmitters are floating in the synapse, a second cell sweeps them up. The amount of different neurotransmitters the second cell receives determines what kind of signal it will fire to the next cells, and the whole process repeats itself. Your brain has successfully communicated an electrochemical message (electro- refers to the electricity the cells use to fire, and –chemical refers to the neurotransmitters).

Ideally, the grand total balance of all of these neurotransmitters moving around keeps your brain functioning properly. Their job is to allow your cells to send regulatory signals to each other to keep you healthy.

However, things can get messed up. For a multitude of genetic, physical, psychological, and environmental reasons, your brain can get out of whack. The most common psychiatric problem – depression – often has to do with a malfunctioning reuptake mechanism.

What is reuptake? Remember that when neurotransmitters leave one cell, they enter a synapse so that a second cell can scoop them up. Once this exchange has finished (and it happens extremely quickly), the first cell gathers up whatever chemicals didn’t make it to the second cell in a process called reuptake. The point of this is to make the chemical transmission process more efficient: the sooner the synapse is clear of neurotransmitters, the sooner it can be used again.

However, sometimes this reuptake process becomes overactive. To demonstrate, imagine this: You’ve got a chocolate bar that you’ve broken into pieces. You’ve offered to share it with a friend, and whatever they don’t eat, you’ll take back and eat yourself. You (the first cell) set the chocolate (neurotransmitters) in the space (synapse) between you and your friend (the second cell). First, your friend takes as much of the chocolate as they want, and then you take the rest (reuptake). That’s how it’s supposed to work.

Now imagine you’re greedy, and you want more of the chocolate. This time, before your friend has a chance to take the portion they want, you grab a lot of the chocolate and eat it. Now your friend isn’t getting as much as they wanted. If they don’t eat anything else, they won’t have enough energy to get through the day.

This is the rough equivalent of a faulty reuptake mechanism in the brain. When the first cell scoops up too many of the neurotransmitters it sent out, the second cell doesn’t receive enough of them to fire the correct signal to the next cell, and so on.

This can occur with multiple neurotransmitters, including serotonin, which has to do with regulating your emotions. When too much serotonin is gathered out of the synapse by the first cell, the second cell may fire incorrectly because it didn’t receive enough serotonin. If this happens in many of your cells at the same time, the result is that your mood is no longer regulated correctly, and you may become depressed.

One molecule of serotonin.

One fix to this problem is antidepressant medication, or more specifically, a type of antidepressant called selective serotonin reuptake inhibitors, or SSRIs. (Think Prozac, Zoloft, and Paxil, among others.) SSRIs do exactly what you’d expect: they stop, or inhibit, the reuptake process from spiraling into chaos. Ideally, the end result is that more serotonin becomes available for your brain cells to use, and your mood becomes more regulated.

Three common dosages of the SSRI Zoloft: 25, 50, and 100 milligrams.

Remember, you have billions of cells working together to regulate your mood. Many of them must experience a reuptake problem simultaneously in order for you to become depressed. Overactive serotonin reuptake isn’t the only brain malfunction that can cause depression, either; for example, other neurotransmitters like dopamine and norepinephrine may be involved. If this is the case, mood-regulating medication other than SSRIs, like lithium (usually for bipolar disorder) or SNRIs (the “N” stands for norepinephrine) may be more effective.

In this article we’ve touched on some of the most basic functions of the brain, but there’s still a lot left to understand. Your body’s most complex organ has been evolving for hundreds of millions of years, and is still largely a mystery. You have the same number of neurons as about a quarter of the Milky Way Galaxy has stars, according to our best scientific estimates – imagine trying to map that much space!

Though many of the basics of neural functioning are understood, the brain is such a complicated structure that the debate over whether it can even comprehend all of its own components still rages on. Regardless, the goal of neuroscientists is to chip away at the intricate and awesome mystery of our own brains, starting with little more than cells, electricity, synapses, and neurotransmitters.

An artificially colored photograph of brain cells, just a few dozen micrometers (one millionth of a meter) across.

2 thoughts on “The Science Of Depression (Briefly Explained)

  1. Very nice layout of how neurotransmitters work; I’ve never had a very clear understanding of this until now. One of my brothers has bipolar depression and it seems to run in our family. I can see now where this physiological state of affairs could be heritable. I hope you will write more on this.


    1. I certainly will write more about neuroscience! It’s my passion. I’m glad you’re better able to understand what your brother goes through. It’s a complicated process (especially when you add bipolar disorder to the mix), but we’ll map it out someday.


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