Spinal anatomy includes bones, tendons, muscles, ligaments and nerves that promote a combination of strength and flexibility. It includes strong bones, flexible ligaments and tendons, large muscles and sensitive nerves.

The spine is one of the most important parts of the body as it provides strength and structure and protects the sensitive spinal cord. Also known as the vertebral or spinal column, the spine is made up of 24 block–shaped bones called vertebrae and two fused bones below them. The bones of the vertebral column are grouped into several categories:

• Cervical spine (seven vertebrae)
• Thoracic spine (12 vertebrae)
• Lumbar spine (five vertebrae)
• Sacral region (sacrum and coccyx)

At birth, there are usually 33 vertebrae. The sacrum includes five vertebrae that eventually fuse to one bone. The coccyx has three to five vertebrae (typically four) that fuse to one bone. Thus the approximately 33 vertebrae in an infant appear as 26 bones in an adult.

An intervertebral disc separates each of the vertebrae in most people, except the first and second cervical vertebrae. These discs are made up of tough, fibrous type of cartilage that is elastic. They act as shock absorbers between the vertebrae, cushioning the bones from the impact of activities such as jumping or certain forms of exercise. They also add stability to the spine while still allowing for movement between the bones. Each disc is made up of a core of jelly–like material (nucleus pulposus) surrounded by a covering of tough, fibrous material (annulus fibrosis). These discs begin degenerating in early adulthood.

Each vertebra is made up of a main body (ventral segment), and a smaller section called the vertebral or neural arch that includes structures called pedicles and laminae. These sections join together to form an open ring. At the vertebral arch, the vertebrae are joined to one another above and below by two zygapophysial joints, commonly known as Z or facet joints.

In the average male, the vertebral column measures 28 inches (71 centimeters [cm]). In women, the average is 24 inches (61 cm).

The vertebral column is normally curved at various points to help align the head with the pelvis. In the thoracic and sacral regions, the curves are concave anterior, meaning the spine curves forward and outward. An exaggeration of the thoracic curve is called kyphosis, or humpback, caused by conditions including osteoporosis. In the cervical and lumbar regions, the curves are convex anterior, meaning the spine curves inward. An exaggeration of the lumbar curve is called lordosis. Sideways curves are not part of the spine’s normal anatomy, and the condition is known as scoliosis.

The pelvic curve and the thoracic curve are known as primary curves, because they are the two curves that are present in a fetus. The cervical and lumbar curves are known as secondary (compensatory) curves, because they are developed after birth. The cervical curve develops once a child is able to hold the head up (3 to 4 months old) and to sit upright (9 months). The lumbar curve develops when the child begins to walk (12 to 18 months).

The sections of vertebral column include:

• Cervical spine. This is located in the neck. It helps support the weight of the head and protects the brain stem and upper portion of the spinal cord. It includes seven vertebrae. The rotation of the cervical spine primarily comes from the top two segments of the cervical spine, the atlas and the axis, whereas flexion and extension movement (bending forward and backward) comes from the lower cervical vertebral segments. The cervical spine contains a convex curve (a backward C shape). It begins at the base of the skull and continues to the upper part of the back, joining the top of the thoracic spine. This cervical section of the spine is more flexible than other regions, allowing more fluid movement of the head and neck.
  
  The cervical region is at risk for injury from sudden movements, such as whiplash. The vertebrae are smaller than those in the thoracic region and must support the weight of the head. In addition, there is limited muscle support in this small area.
  
  
• Thoracic spine. The center portion of the spine located in the upper back. The rib cage attaches firmly at each level of the thoracic spine, providing stability and structural support to the upper back. In this way, the thoracic spine helps protect the heart and lungs. The thoracic spine contains a concave curve (C shape). This curve begins in the middle of the second thoracic vertebra and ends at the middle of the 12^th thoracic vertebra.
  
  Because this area of the upper back is not designed for motion, injuries to the thoracic spine are less common. In addition, the thoracic spine has larger vertebrae than the cervical and stronger muscles, allowing greater support and protection. Ribs are also attached to these vertebrae, giving additional support.
  
  
• Lumbar spine. The lowest section of the spine located below the thoracic spine. The vertebrae in the lumber region are the largest in the spine. The lumbar spine contains a convex curve (backward C) similar to the cervical spine. It begins in the middle of the thoracic vertebra and ends at the base of spine. This curve is more marked in females than in males.
  
  The lumbar region allows flexibility and strength in the spine. It is one of the most frequent areas for injury as it holds most of the body’s weight. People tend to place undo pressure on the lumbar region with lifting and twisting movements. Improper lifting or repetitive movements often cause lower back pain.
  
  
• Sacral region. Just below the lumbar spine is the sacral spine or sacrum. The sacrum is a large triangle-shaped bone that makes up the back part of the pelvis. It connects the spine to the lower half of the body. The sacroiliac joints, which connect the sacrum to the pelvis, contain some of the strongest ligaments in the body. They are responsible for the stability and strength at the lower end of the spine.
  
  Below the sacrum is the coccyx, more commonly known as the tailbone. It is the very bottom of the spine and marks the end of the spinal column. Most injuries in the sacral region occur where the lumbar and sacral regions connect. This area is subject to stress from many daily activities.

The vertebral column supports the body weight of the head and trunk, and provides protection for the spinal cord. It is primarily responsible for a person’s posture and contributes to the strength and flexibility of the body.