Your back has many interconnecting structures including: bones, joints, muscles, ligaments and tendons. It's main support structure is the spine, which is made up of 24 separate bones called vertebrae plus the bones of the sacrum and coccyx. Between the vertebrae are discs that act as shock absorbers and allow your spine to bend. Your spinal cord threads down through the central canal of each vertebra, carrying nerves from your brain to the rest of your body.
Attribution: BUPA