Anatomy of the Spine

The spinal column is the body's main support structure. Its thirty-three bones, called vertebrae, are divided into five regions: cervical, thoracic, lumbar, sacral and coccygeal.



The spine consists of 33 individual bones. It provides the foundation of support for the body, enabling a person to perform basic movements such as standing upright and bending. The spinal cord, protected by these bones, connects nerves throughout the body to the brain, providing function and movement to every area of the body. Ligaments and tendons attach muscles to the bones of the spine, keeping them properly aligned and united. The spine can be injured by direct trauma to the bones and tissues that surround the spinal cord. Spinal injuries are usually serious and require medical attention.

Muscles, Ligaments and Joints of the Spine

Two muscle groups that affect the spine are extensors and flexors. The extensor muscles, attached to the back of the spine, enable a person to stand up and lift objects. The flexor muscles are located at the front of the spine and include the abdominal muscles. The flexor muscles enable people to bend forward and also control the arch in the lower back. If any of these muscles become misaligned, there can be incredible strain placed on the spine.

Ligaments are strong, fibrous bands that stabilize the spine and protect spinal discs. The three major ligaments of the spine are the ligamentum flavum, anterior longitudinal ligament and posterior longitudinal ligament, and they prevent excessive movement of the vertebral bones.

Facet joints of the spine allow for movement of the back. Each vertebra contains four facet joints, one pair of which connects to the vertebra above on each side and a second pair that connects to the vertebra below on each side.

Vertebrae of the Spine

The vertebrae of the spine are the 33 individual bones that interlock with one another to form the spinal column. They are divided into five different regions. The vertebrae in each region have unique features provide proper function. The regions of the spinal vertebrae are:

Cervical

Found in the neck area, the main function of the cervical spine is to support the weight of the head.

Thoracic

Located in the mid back, the thoracic spine holds the rib cage in place, protecting the heart and lungs. There are 12 thoracic vertebrae, which move but have a limited range of motion.

Lumbar

The lumbar spine, or lower back, bears the full weight of the body. There are five lumbar vertebrae, numbered from L1 to L5. These vertebrae are much larger in size than those found in other areas of the spine, helping them absorb the impact and stress of lifting and carrying heavy objects.

Sacrum

The main function of the sacrum is to connect the spine to the hip bones. There are five sacral vertebrae, which are fused together and cannot be moved.

Coccyx

The coccyx, or tailbone, is made up of four fused bones that provide attachment for ligaments and muscles of the pelvic floor. Like the sacrum, vertebrae of the coccyx do not move.

Intervertebral Discs of the Spine

Each vertebra of the spine is separated and cushioned by an intervertebral disc, which keeps the bones from rubbing together. Intervertebral discs contain a gel-filled center, known as the nucleus, which is composed mainly of fluid that helps maintain its shape and height. With age, the discs increasingly lose some level of this fluid and become brittle and flatter, causing most people to become shorter as they age. Additionally, diseases such as osteoarthritis and osteoporosis can cause bone spurs to grow, irritating the nearby disc. Injury or strain may also cause discs to bulge or herniate.

The Spinal Cord

The spinal cord runs down the back through the spinal canal from the brain stem to the first lumbar vertebra. At the end of the spinal cord, cord fibers separate and continue down through the spinal canal to the tailbone before branching off to the legs and feet. The brain sends out motor messages to the limbs and the body through the spinal cord. The spinal cord branches off into a vast network of nerves, which act as message carriers between the spinal cord and the rest of the body, controlling movement and sensation.

Any type of injury to the spinal cord can be debilitating. Injury to the thoracic or lumbar spinal area, for example, may cause motor and sensory loss of the legs, known as paraplegia. Injury to the cervical spinal area may cause sensory and motor loss of the arms and legs, which is known as quadriplegia.

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