Back Basics

Your spine is made up of vertebrae, discs, spinal cord and nerves, ligaments, and muscles.

Vertebrae

Your spine is a column of 33 bones (vertebrae) stacked up on top of each other. As shown below, the spinal column is divided into four regions, and the vertebrae within each region are numbered.

Discs

The vertebrae are separated by discs that cushion the vertebrae and allow them to move freely. Each disc is a small, circular capsule with a tough outer wall (the annulus) and a softer core (the nucleus). In children, this core is more fluid-gel-like—but with age, the core tends to become harder and less elastic.

Facet joints

Each vertebra has two pairs of facet joints. These joints link the vertebrae together at the back of your spine. They stabilize the spine and allow you to bend and twist. To help the joints glide smoothly against each other as you move, the joint surfaces are covered by cartilage and the whole joint is covered by a capsule containing fluid. This joint capsule is made of ligaments and other connective tissue.

Spinal cord and nerves

Besides supporting the weight of your body, the spine also houses and protects your spinal cord. The spinal cord is a network of nerves that goes from the base of your brain down to your lower back. (The spinal cord passes through a tubular space — the spinal canal — formed by the ring-shaped openings of the vertebrae.) Smaller spinal nerves branch off of the spinal cord, fitting through smaller spaces between your vertebrae to reach all areas of your body.

Ligaments

The vertebrae are connected and supported by ligaments. The two main spinal ligaments run the length of the spinal column.

Muscles

The entire spinal column is stabilized by muscles in your back, sides, and abdomen. These muscles hold your posture and help you to bend, twist, and move your back.

Abnormal curvature

Your spine's natural curves help balance your body. But if the curves become too pronounced — or if your spine develops a twist or an extra curve — it puts extra pressure on the vertebrae and discs. This can cause instability and bulging or herniated discs. Abnormal curvatures include those shown below.

• Scoliosis - a side-to-side curve in your back
• Kyphosis - increased curve (“hump”) in your upper back
• Lordosis - increased curve in your lower back (“swayback”)

Fractures

Like any bones, your vertebrae can crack or break. Reasons for a spine fracture include an injury, repeated stress, or a condition like osteoporosis, which can make bones weak and brittle.

Degenerated disc

Degenerative disc disease (DDD) is a catch-all term to describe changes—usually thinning, hardening, and drying out—in your spinal discs. Disc degeneration can result from normal aging or wear-and-tear, but it's sometimes begun or sped up by injury, disease, or unusual stress. Degenerated discs can irritate the spinal nerves and cause instability. They can be painful.

Bulging disc

If the outer wall of a spinal disc weakens, it may push out (bulge) toward the nerves. This can cause painful nerve irritation.

Herniated disc (also called ruptured disc)

If the outer wall of a spinal disc tears (ruptures), the soft material inside the disc can squeeze out and press on nearby nerves. This can cause pain, numbness, or weakness in your legs or back.

Instability

Spinal instability is when adjoining vertebrae slip back and forth, or have permanently shifted out of position. This instability can be caused by a damaged spinal disc, a bone injury, arthritis in the facet joints, or just something you were born with. The slippage can irritate the bone, disc, spinal cord, and nerves.

Stenosis

Stenosis is a narrowing of the spinal canal. Stenosis can press on the spinal cord and nerves and cause pain and other symptoms.

Nerve problems

All of the conditions described above can irritate or press on (“pinch”) the spinal cord or nerves. This can cause pain, numbness, weakness, and other problems throughout your body. Common examples are lumbar radiculopathy or sciatica (nerve problems in your lower spine, causing leg pain) and cervical radiculopathy (nerve problems in your neck, causing arm pain).