Spine Anatomy

The human spine is a complex anatomic structure that is the scaffolding for the entire body. It provides several important functions, including:

  • Protecting the spinal cord and nerves
  • Structural support for the body, allowing us to stand upright. The spine supports about half the weight of the body, and the muscles support the other half.
  • Moving easily and flexibly in many planes around the body. The spine makes all the movements of the head, arms and legs possible.

The average person is born with about 33 individual bones (the vertebrae) that interact and connect with each other through flexible joints, or facets. By the time a person becomes an adult most have only 24 vertebrae because some vertebrae at the bottom end of the spine fuse together during normal development. Sometimes a person may have an additional vertebra, which is called a transitional body and is usually found at the sixth level of the lumbar area (labeled L6).

The bottom of the spine is called the sacrum. It is made up of several vertebral bodies usually fused together as one. The remaining small bones or ossicles below the sacrum are also fused together and called the tailbone or coccyx. The spine above the sacrum consists of:

The spine combines strong bones, unique joints, flexible ligaments and tendons, large muscles and highly sensitive nerves. While most of us take the benefits of a healthy spine for granted, spinal pain is a sharp reminder of how much we depend on the spine in daily life. Some causes of spinal pain include:

  • Irritation of the large nerves as they exit the bony confines of the spine leading to the arms and legs
  • Irritation of the smaller nerves of the spine that involve innervate or supply the discs between the vertebrae, facets and ligaments
  • Strain of the large muscles of the back that hold the spine upright
  • Injuries to the bones, ligaments or joints
  • Damage or disease to the discs that separate the bones of the spine
  • Abnormal slippage or movement between segments
  • Tumors, infection, trauma, deformity or other spinal disorders

The spinal column is made up of many parts, all designed to help the back move flexibly, support body weight and protect the spinal cord and nerves. These parts include the: