Dear Trevor,
Everything we do and think is thanks to the 3-pound organ tucked into our skulls. But what is it made of?
I asked my friend Samantha Gizerian. She’s a brain scientist at Washington State University.
She told me the brain is surprisingly soft and mushy.
“We think about our other organs and tissues, and they’re squishy in a very solid way,” Gizerian said. “Like when you go to the grocery store and get a carton of meat. You can squish on the steak, right? Our other organs are mostly like that as well. But the brain is very, very delicate.”
She told me it’s more like the ground up burger people use to make meatballs. Or like soft tofu or a Jello square.
The brain is extra soft because it’s about 60% fat.
Most of that fat coats the long tails of your brain cells, which are called axons. Electrical signals run down an axon to send messages through the brain and body. The fat combines with proteins to make a coat that wraps around it—called myelin. That coat keeps those electrical signals running smoothly.
Fat also stores energy. Having a heaping helping of fat in your brain means your body can quickly turn that fat into the sugar it needs for fuel.
Plus, an insulating layer of fat helps keep your brain at just the right temperature.
The remaining 40% of your brain is proteins, sugars, water and salts. Your brain uses the salts—like sodium and potassium—to make the electrical charge that your brain cells use to send signals.
So, let’s say we crack open a human skull and begin unboxing it. What would we see?
Just under the skull bones, there’s a thin covering of membranes called the meninges. They protect your brain. They provide structure so your mushy brain doesn’t move around too much.
The meninges also anchor the blood vessels that remove waste and carbon dioxide from your brain. Blood bringing oxygen and nutrients comes up to the brain via vessels that are in either side of your neck. The right side brings blood to the right side of your brain. The left side brings it to the left side of your brain. When the brain has used up the oxygen and nutrients, the blood flows out through veins in the meninges.
Your brain sits under the meninges. It has two layers—called gray matter and white matter.
“When you look at the brain and see both hemispheres, you see the gray matter on the outside and the white matter on the inside,” Gizerian said. “The neurons are just that thin gray outside part. The white part is supporting cells and the axons.”
In fact, only about 10% of your brain is actually brain cells, which are also called neurons. The rest of the brain is mostly those long, fat-coated tails called axons and supporting cells called glia. They help your brain cells work and give structure to your mushy brain.
Your brain also gets support from deep inside. That’s where you have ventricles that make cerebrospinal fluid. That’s the liquid that bathes your brain and spinal cord.
“Cerebrospinal fluid basically leeches out of the walls of the ventricles, then flushes through and down into the spinal column,” Gizerian said. “What’s neat about this is the ventricle actually holds water like a water balloon—and it keeps the brain from squishing in on itself.”
It’s hard to imagine that something as delicate and squishy as the brain is the reason we can understand each other and the world around us.
It’s pretty amazing, if you’re axon me.
Sincerely,
Dr. Universe