Your backbone (vertebral column) is actually a stack of more than 30 bones called vertebrae. Together they create a bony canal that surrounds and protects your spinal cord. Small nerves enter and exit the spinal cord through spaces in your vertebrae.
The vertebrae are held together by muscles, tendons and ligaments. Between the vertebrae are intervertebral disks, which act as shock absorbers by preventing the vertebrae from hitting one another when you walk, run or jump. The intervertebral disks also allow your spine to twist, bend and extend.
The lower back — which carries most of your weight — is the site of most back pain. Here are some of the most common culprits.