Supporting the spine, while providing it flexibility, are ligaments (tough bands of connective tissue that attach bone to bone) and muscles. Two main ligaments are:

• anterior longitudinal ligament
• posterior longitudinal ligament.

Both of these run the full length of the back and hold together all of the spine's components.

The two main muscle groups involved in back function are:

• The extensors, which include the many muscles that attach to the spine and work together to hold your back straight while enabling you to extend it.
• The flexors
, which attach at your lumbar spine (lower back), and enable you to bend forward. Located at the front of your body, the flexors include your abdominal and hip muscles.

Although the spine is a continuous structure, it is often described as if it were five separate units. These units are the five different sections of the spine:

1. The cervical spine – the neck and upper back, composed of the seven vertebrae closest to the skull. The cervical spine supports the weight and movement of your head and protects the nerves exiting your brain.
2. The lumbar spine – the lower back, composed of five vertebrae, provides support for the majority of your body's weight.
3. The thoracic spine
– the middle back, made up of the 12 vertebrae in between the cervical and lumbar spine.
4. The sacrum – the base of the spine that is composed of five vertebrae fused (joined together) as one solid unit. The sacrum attaches to ilium of the pelvis, forming the sacroiliac joints.
5. The coccyx
– the "tailbone" located below the sacrum, composed of four fused vertebrae.