Spine Structure and Function

What is the spine?

Your spine, or backbone, is your body’s central support structure. It connects different parts of your musculoskeletal system. Your spine helps you sit, stand, walk, twist and bend. Back injuries, spinal cord conditions and other problems can damage the spine and cause back pain.

What are the parts of the spine?

A healthy spine has three natural curves that make an S-shape. These curves absorb shocks to your body and protect your spine from injury. Many different parts make up your spine:

• Vertebrae: The spine has 33 stacked vertebrae (small bones) that form the spinal canal. The spinal canal is a tunnel that houses the spinal cord and nerves, protecting them from injury. Most vertebrae move to allow for a range of motion. The lowest vertebrae (sacrum and coccyx) are fused together and don’t move.
• Facet joints: These spinal joints have cartilage (a slippery connective tissue) that allows vertebrae to slide against each other. Facet joints let you twist and turn, and they provide flexibility and stability. These joints can develop arthritis and cause back pain or neck pain.
• Intervertebral disks: These flat, round cushions sit between the vertebrae and act as the spine’s shock absorbers. Each disk has a soft, gel-like center (the nucleus pulposus) surrounded by a flexible outer ring (the annulus). Intervertebral disks are under constant pressure. A herniated disk can tear, allowing some of the nucleus’ gel substance to leak out. Herniated disks (also called bulging, slipped or ruptured disks) can be painful.
• Spinal cord and nerves: The spinal cord is a column of nerves that travels through the spinal canal. The cord extends from the skull to the lower back. Thirty-one pairs of nerves branch out through vertebral openings (the neural foramen). These nerves carry messages between the brain and muscles.
• Soft tissues: Ligaments connect the vertebrae to hold the spine in position. Muscles support the back and help you move. Tendons connect muscles to bone and aid movement.

What are the spine segments?

The 33 vertebrae make up five distinct spine segments. Starting at the neck and going down toward your buttocks (rear end), these segments include:

• Cervical (neck): The top part of the spine has seven vertebrae (C1 to C7). These neck vertebrae allow you to turn, tilt and nod your head. The cervical spine makes an inward C-shape called a lordotic curve.
• Thoracic (middle back): The chest or thoracic part of the spine has 12 vertebrae (T1 to T12). Your ribs attach to the thoracic spine. This section of the spine bends out slightly to make a backward C-shape called the kyphotic curve.
• Lumbar (lower back): Five vertebrae (L1 to L5) make up the lower part of the spine. Your lumbar spine supports the upper parts of the spine. It connects to the pelvis and bears most of your body’s weight, as well as the stress of lifting and carrying items. Many back problems occur in the lumbar spine. The lumbar spine bends inward to create a C-shaped lordotic curve.
• Sacrum: This triangle-shaped bone connects to the hips. The five sacral vertebrae (S1 to S5) fuse as a baby develops in the womb, which means they don’t move. The sacrum and hip bones form a ring called the pelvic girdle.
• Coccyx (tailbone): Four fused vertebrae make up this small piece of bone found at the bottom of the spine. Pelvic floor muscles and ligaments attach to the coccyx.

What conditions and disorders affect the spine?

Up to 80% of Americans experience back pain at some point. Vertebrae and disks can wear down with age, causing pain. Other conditions that affect spine health include:

• Arthritic conditions, such as ankylosing spondylitis (AS).
• Back strains and sprains.
• Birth defects such as spina bifida.
• Bone spurs (jagged edges on vertebrae that put pressure on the spinal cord and nerves).
• Curvatures of the spine (scoliosis and kyphosis).
• Neuromuscular diseases, such as amyotrophic lateral sclerosis (ALS).
• Nerve injuries, including spinal stenosis, sciatica and pinched nerves.
• Osteoporosis (weak bones).
• Spinal cord injuries, including spinal fractures, herniated disks and paralysis.
• Spine tumors and cancer.
• Spine infections like meningitis and osteomyelitis.

How can I keep my spine healthy?

Strong back muscles can protect your spine and prevent back problems. Try to do back-strengthening and stretching exercises at least twice a week. Exercises like planks strengthen the core (abdominal, side and back muscles) to give your spine more support. Other protective measures include:

• Bend your knees and keep your back straight when lifting items.
• Lose weight, if needed (excess weight strains your back).
• Maintain good posture.

When should I call the doctor?

You should call your healthcare provider if you experience:

• Back pain with fever.
• Bowel or bladder control issues.
• Leg weakness or pain that moves from your back down your legs.
• Pain that worsens, causes nausea or sleeplessness or interferes with daily activities.