The muscles next to the spine are called the paraspinal muscles. They support the spine and are the motor for movement of the spine. Joints allow flexibility, and muscles allow mobility. There are many small muscles in the back. Each controls some part of the total movement between the vertebrae and the rest of the skeleton. These muscles can be directly injured, such as when you have a pulled muscle or muscle strain. They can also cause problems indirectly, such as when they are in spasm after injury to other parts of the spine.
A muscle spasm is experienced when your muscle tightens up and will not relax. Spasms usually occur as a reflex (meaning that you cannot control the contraction). When any part of the spine is injured-including a disc, ligament, bone, or muscle-the muscles automatically go into spasm to reduce the motion around the area. This mechanism is designed to protect the injured area.
Muscles that are in spasm produce too much lactic acid, a waste product from the chemical reaction inside muscle cells. When muscles contract, the small blood vessels traveling through the muscles are pinched off (like a tube pinched between your thumb and finger), which causes a build up of lactic acid. If the muscle cells cannot relax and too much lactic acid builds up, it causes a painful burning sensation. The muscle relaxes as the blood vessels open up, and the lactic acid is eventually washed away by fresh blood flowing into the muscle.