The spinal cord is a collection of nerves that transmit the messages from the brain to the various muscles, tissues and organs of the body. The nerves leave the spinal cord through holes or openings between each vertebral body. The discs are the cushions between each vertebral body. They serve as a shock absorber to prevent the vertebral bodies from rubbing against each other. The disc contains a tough outer ring of fibrous tissue called the annuls and a softer sponge-like tissue in the center or nucleus pulposus.
Most people have low back pain as a result of mechanical factors.
The majority will have their pain as a result of strained muscles or ligaments or inflammation of the joints between the vertebral bodies. Aggravating factors include overweight, poor posture or lack of physical exercise. Even lack of exercise can produce stiffness in the back and muscle spasms. A herniated or slipped disc occurs when the disc protrudes from its normal position between the vertebral bodies. The protruded disc can put pressure on the spinal nerves as they leave through the openings between the vertebral bodies.