The spine provides framework to support the body and protect the spinal cord. When viewed from the front or back, it should be straight, but when viewed from the side, it should have three gradual curves.
Humans are born with 33 spine segments called vertebrae. The lower 5 sacral and 4 coccyx vertebrae fuse together to form a base for the spine and the back of the pelvis. The remaining 24 separate vertebrae increase in size and strength from the top to the bottom for increased weight bearing. They are similar in structure except the top two which support the skull.
The cervical spine (C1-C7) is the top 7 vertebrae which support the neck and skull with an inward curve called lordosis.
The thoracic spine (T1-T12) is the upper back which supports the shoulders with an outward curve called kyphosis. Rib bones connect to both sides of the thoracic vertebrae forming the rib cage which protects the heart and lungs.
The lumbar spine (L1-L5) is the lower back which supports the most body weight and curves inward (lordosis).
The round front section of each vertebrae is the body which functions to support weight. Pedicles are side projections connecting the body to the lamina. The lamina forms the back of the arch with two top projections and two bottom projections which connect to discs above and below to form capsular facet joints providing rotation.
Two transverse processes are located on either side of the bony arch. The rear-most projection is the spinous process, felt through the skin as the ridge of bumps in the center of the neck and back. These processes provide attachment points for muscles and ligaments.
Protective openings on each side of adjoining vertebrae are neural foramen through which nerves pass out of the spinal canal.
The spinal canal contains the spinal cord which extends from the base of the brain to the area between L1-L2. It then divides into a bundle of individual nerve roots called the cauda equina (meaning horse's tail) which travels to the legs, bowels, bladder and genitals. The thecal sac surrounds the spinal cord and cauda equina, composed of a dura mater membrane filled with cerebral spinal fluid.
Small cushions called intervertebral discs are located between the vertebral bodies to provide flexibility and act as shock absorbers. They are composed of two parts, the strong outer ring of fibers called the annulus which connects the vertebrae together and the soft, spongy center
which is the nucleus.
A well-hydrated nucleus is tall and provides sufficient space for nerves to pass through the foramen and for facet joints to fit together properly. It maintains the spine's normal curvature and proper ligament tension allowing some movement while maintaining spinal canal alignment.
When discs deviate from normal or are removed without replacement, the anatomy of the spine changes which may lead to back failure.