Gut brains

The human gastrointestinal tract has half a billion neurons embedded in its lining. Often described as the “second brain,” it can act and react autonomously, and even has its own supply of serotonin and dopamine.

Fr. Leuret et P. Gratiolet [CC BY 4.0 (
I like writing about the gut and the gastrointestinal tract. That pink squishy tube that runs from our mouths to the other end is a glorious chorus of weird science, from the cells shaped like Medieval goblets that produce mucus (the goblet cells) to the sound of your gut rumbling (delightfully and onomatopoeically known as borborygmus).

The strangest fact about the gut is this: it has its own brain. You may have heard the myth that dinosaurs had two brains – alas, this one is not true, just a misunderstanding about a stegosaurus butt. But humans have 500 million neurons packed into the lining of the gut. That’s not a lot compared to our primary brain (which has around 85 billion neurons), but it’s about the same number of neurons as a dog (whose brains clock in at 530 million neurons).

It’s often called the “second brain” because many of its functions can be carried out independently of the brain up top. Sure, it gets instructions from the brain to carry out its reflex actions, but even when the connection to the brain is severed the gut can just keep on ticking.

This collection of neurons is known formally as the enteric nervous system. It has its own supply of neurotransmitters – in fact, most of the human body’s supply of serotonin lies in the gut, and half of its supply of dopamine. Incredible. I wonder if we get gut emotions?

By the way, I went with “gut brains” for the title of this post, but it could also have been “think from your gut” or (thanks to my beloved wife for this suggestion) “s**t for brains.”


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