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The structures that make up the back

The back is an intricate structure of bones, muscles, and other tissues that form the posterior part of the body’s trunk, from the neck to the pelvis. The centerpiece of this structure is the spinal column, which not only supports the upper body’s weight, but houses and protects the spinal cord; the delicate nervous system structure that carries signals that control the body’s movements and convey its sensations.

Stacked on top of one another are more than 30 bones, the vertebrae, that form the spinal column also known as the spine. Each of these bones contains a roundish hole that, when stacked in register with all the others, creates a channel that surrounds the spinal cord. The spinal cord descends from the base of the brain and extends in the adult to just below the rib cage. Small nerves (roots) enter and emerge from the spinal cord through spaces between the vertebrae.

Because the bones of the spinal column continue growing long after the spinal cord reaches its full length in early childhood, the nerve roots to the lower back and legs extend many inches down the spinal column before exiting. The spaces between the vertebrae are maintained by round, spongy pads of cartilage called inter-vertebral discs that allow for flexibility in the lower back and act much like shock absorbers throughout the spinal column to cushion the bones as the body moves. Bands of tissue known as ligaments and tendons hold the vertebrae in place and attach the muscles to the spinal column.

The lower region of the back, where most back pain is felt, supports the weight of the upper body. There are numerous reasons that lead to back pain and that put this intricate structure at risk.

As people age, bone strength and muscle elasticity and tone tend to decrease. The discs begin to lose fluid and flexibility, which decreases their ability to cushion the vertebrae.

Pain can occur when, for example, someone lifts something too heavy or overstretches, causing a sprain, strain, or spasm in one of the muscles or ligaments in the back. If the spine becomes overly strained or compressed, a disc may rupture or bulge outward. This rupture may put pressure on one of the more than 50 nerves rooted to the spinal cord that control body movements and transmit signals from the body to the brain. When these nerve roots become compressed or irritated, back pain results.

Most low back pain follows injury or trauma to the back, but pain may also be caused by degenerative conditions such as arthritis or disc disease, osteoporosis or other bone diseases, viral infections, irritation to joints and discs, or congenital abnormalities in the spine. Obesity, smoking, weight gain during pregnancy, stress, poor physical condition, posture inappropriate for the activity being performed, and poor sleeping position may also contribute to low back pain. Additionally scar tissue created when the injured back heals itself does not have the strength or flexibility of normal tissue. Buildup of scar tissue from repeated injuries eventually weakens the back and can lead to more serious injury.