A stack of bones
Your backbone is not one long bone. It is a stack of small bones called vertebrae. You say it like VER-tuh-bray. Just one is called a vertebra.
Each vertebra has a thick, round part in front, like a spool. At the back is a ring of bone. When they are stacked up, the rings make a long tunnel.
Try it: bend forward and ask a grown-up to gently run a finger down the middle of your back. Those bumps are the back parts of your vertebrae.
Five parts, top to bottom
Your neck has 7 vertebrae. They are small, and they let you nod, tilt and turn your head.
Your upper back has 12. Each one holds on to a pair of ribs.
Your lower back has 5 big, strong ones. They carry the most weight.
Below them is the sacrum, a triangle of bone at the back of your hips. At the very bottom is your tailbone.
33 bones become 26
When you are little, your backbone has about 33 vertebrae. But a grown-up's backbone is counted as 26 bones. Did some go missing?
No! The bottom ones join together. Five of them slowly join into the sacrum, one solid bone. About four tiny ones at the very end join into the tailbone.
This joining happens slowly, through the teen years and into the early grown-up years. So a grown-up has 24 vertebrae that move, plus the sacrum and the tailbone. That makes 26.
Cushions in between
Between your vertebrae are round cushions called discs. Each disc has a tough ring on the outside and a soft, squishy middle, a bit like a jelly donut.
The discs soak up bumps when you walk, run and jump. They also let your backbone bend.
During the day, your weight presses on the discs and squeezes out a little water. At night, lying down, they soak it back up. So you're a tiny bit taller in the morning, about 1 centimeter. That's about the width of a pea!
Astronauts in space can grow a few centimeters taller, because nothing presses their discs down. They shrink back when they come home to Earth.
A tunnel for your spinal cord
The rings at the back of your vertebrae line up into a tunnel. Inside it runs your spinal cord, a thick bundle of nerves.
Your spinal cord carries messages between your brain and your body. It tells your feet to step. It tells your brain when your toes are cold.
The bony tunnel keeps this important cable safe, the way a pipe keeps wires safe inside a wall.
The S-shaped curve
From the side, a healthy backbone isn't straight. It curves gently, like a long letter S. Your neck curves in, your upper back curves out, and your lower back curves in again.
The S works like a spring. It helps carry your weight and soften every step.
Babies are born with a back curved like a letter C. The neck curve forms when they learn to hold up their heads. The low back curve forms when they start to stand and walk.