A vertebra is one of the small bones that stack together to form your spine, or backbone. If you run your finger down the middle of someone's back, you can feel the bumps of these bones lined up like a tower of wooden spools on a string.

Your spine contains 33 vertebrae (that's the plural form), each shaped roughly like a ring with some knobs sticking out. They fit together in a way that lets you bend and twist while still protecting the delicate spinal cord running through the center of the spine. Think of it like flexible plumbing: each piece is solid, but the connections between them allow movement.

Different sections of your spine have differently shaped vertebrae. The ones in your neck are smaller and let you turn your head, while the ones in your lower back are larger and stronger to support your body's weight. Animals with backbones, called vertebrates, all have vertebrae too: a snake might have over 300, while a giraffe has only seven in its very long neck (the same number as you!).

If a vertebra gets injured or breaks, it's serious because of that crucial spinal cord nearby. This is one reason helmets and other protective gear are important in activities where you might fall or get hit.