The spine is made up of stacks of bones called vertebrae, which are divided into five sections. The neck, also known as the cervical spine, has seven vertebral bones. The mid-back, referred to as the thoracic spine, has twelve vertebrae. The low back, or lumbar spine, has five vertebrae. Given the number of spinal bones, humans enjoy a wide range of motion when everything is functioning correctly.
At the foundation or base of the spine, a triangular-shaped bone called the sacrum connects the spine above with the two pelvic bones on either side. At the point where the sacrum and pelvis connect, there is a large joint called the sacroiliac joint or SI joint. The SI joint is a common area for the development of pain in the lower back. Underneath the sacrum sits the coccyx or “tailbone.”
The vertebrae have an opening through which the spinal cord passes. These bones, therefore, protect the spinal cord as it descends from the brain. Each of the vertebral bones connect above and below by a pair of joints called facet joints. In addition to these facet joints, a detailed framework of muscles and ligaments provide additional structural stability and allow movement.
- Vertebral body
- The entire bone of a single level of the spine
- Spinous process
- Bony prominence that connects the back of the vertebrae to one another through ligament attachments.
- Transverse processes
- Bony prominence on either side that with tendon/muscle attachments. The muscles act here to stabilize and support the spine.
- Facet joints
- Interlocking portions of bone that connect the vertebrae to one another from above and below. These joints stabilize the spine and prevent excessive rotation of the back.
- Spinal canal
- Hollow tunnel through which the spinal cord passes located behind the vertebral bodies.