Spine Structure and Function

What is the spine?

The spine, or backbone, is a bony structure that supports your body. It connects different parts of your musculoskeletal system, which includes your body’s bones and muscles. Your spine helps you sit, stand, walk, twist and bend.

What does the spine do?

Your spine has several important functions, including:

• Giving your body structure (shape).
• Supporting your body (posture).
• Protecting your spinal cord (nerves that connect your brain to the rest of your body).
• Allowing you to be flexible and move.

Where is the spine located?

Your spine is the long column of bones that extend from your neck to your lower back. Your spine starts at the base of your skull (head bone) and ends at your tailbone, a part of your pelvis (the large bony structure between your abdomen and legs).

What does the spine look like?

A healthy spine has three natural curves that make an S-shape. These curves work as shock absorbers to protect your spine from injury.

Several bones and soft tissues make up your spine. They connect like bricks, stacked one on top of the other and help support your body in different ways.

What are the parts of the spine?

• Vertebrae: Your spine has 33 stacked vertebrae (small bones) that form the spinal canal. The spinal canal is a tunnel that houses your 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.
• Intervertebral disks: These flat, round cushions sit between the vertebrae and act as your spine’s shock absorbers. Each disk has a soft, gel-like center (nucleus pulposus) surrounded by a flexible outer ring (annulus fibrosus). Intervertebral disks are under constant pressure, which may cause the nucleus pulposus to squeeze out and contact nerves, leading to symptoms like sciatica.
• Spinal cord and nerves: Your spinal cord is a column of nerves that travels through your spinal canal. The cord extends from your skull to your lower back. Thirty-one pairs of nerves branch out through vertebral openings (neural foramen). These nerves carry messages between your brain and muscles.
• Soft tissues: Ligaments connect the vertebrae to hold your spine in position. Muscles support your spine and help you move. Tendons connect muscles to bone and help prevent muscle injury while aiding in movement.

What are the segments of the spine?

Thirty-three vertebrae make up five distinct spine segments. Starting at your neck and going down toward your tailbone, the segments of your spine include:

• Cervical spine (neck): The top part of your 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 spine (middle back): The thoracic part of your spine has 12 vertebrae (T1 to T12). Your ribs attach to the thoracic spine. This section of your spine bends out slightly to make a backward C-shape called a kyphotic curve.
• Lumbar spine (lower back): Five vertebrae (L1 to L5) make up the lower part of your spine. Your lumbar spine supports the upper parts of your spine. It connects to your pelvis and bears most of your body’s weight, as well as the stress of lifting and carrying items. The lumbar spine bends inward to create a C-shaped lordotic curve.
• Sacrum: This triangle-shaped bone connects to your hips. The five sacral vertebrae (S1 to S5) fuse (weld together) during fetal development, 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 your spine. Pelvic floor muscles and ligaments attach to the coccyx.

What are common conditions that affect the spine?

Your spine plays an important role in your daily life. It gets a lot of wear and tear, putting it at risk for damage and injuries. Common conditions that affect spine health include:

• Arthritis and arthritic conditions, like ankylosing spondylitis.
• Back strains and sprains.
• Birth defects such as spina bifida.
• Bone spurs.
• Curvatures of the spine (scoliosis and kyphosis).
• Herniated disk.

Other spine conditions include:

• Neuromuscular diseases, such as amyotrophic lateral sclerosis.
• Nerve injuries, like spinal stenosis, sciatica and pinched nerves.
• Osteoporosis.
• Spinal cord injuries, including spinal fractures and paralysis.
• Spine tumors and cancer.
• Spine infections, like meningitis and osteomyelitis.

What are common signs or symptoms of spine conditions?

The most common symptom of spine conditions is back pain or neck pain. Up to 80% of Americans experience back pain at some point in their life.

Other signs and symptoms of spine conditions include:

• Muscle spasms.
• Loss of bowel or bladder control.
• Weakness or numbness in your limbs (arms and legs).
• Paralysis.

What tests check the health of my spine?

A healthcare provider may use the following tests to check the health of your spine:

• Imaging tests (X-ray, CT scan, MRI).
• Blood tests.
• Electromyography (EMG).
• DEXA (DXA) bone density test.
• Spinal tap (lumbar puncture).

How are spine conditions treated?

Treatment for each spine condition varies based on the type. Common treatments for spine conditions may include:

• Physical therapy, acupuncture, massage therapy and chiropractic adjustments.
• Medications (anti-inflammatories, muscle relaxants, etc.).
• Injections (epidural steroid injections, nerve blocks, etc.).
• Spine surgery (discectomy, foraminotomy, fusion, etc.).

How can I keep my spine healthy?

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

Other protective measures include:

• Bending your knees and keeping your back straight when lifting items.
• Maintaining a healthy weight.
• Using good posture (sitting up straight, not slouching).

Talk to a healthcare provider about how you can keep your spine and other bones healthy.

When should I call my healthcare provider?

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 to your legs.
• Numbness in your arms or legs.
• Pain that worsens, causes nausea, sleeplessness or interferes with daily activities.