Spine anatomy.
Stronger than you think.
Your spine is an impressive structure that provides both stability and flexibility. It is a common misconception that the back is fragile. In reality, your back is designed to move, carry and bend.
Explore your spine
Tap a region for more info
Carries your head (about 5 kg) and is the most mobile part of your spine. This is where nodding and turning happen.
Connected to your ribs, which makes this region extra stable. It protects your heart and lungs.
The largest and strongest vertebrae: they carry most of your body weight. Most back pain occurs here, not because this region is weak, but because it works the hardest.
Fused vertebrae that connect your spine to your pelvis. A solid base that transfers forces to your legs.
Vertebrae
Your spine consists of 33 vertebrae, divided into 5 regions: 7 cervical (neck), 12 thoracic (middle), 5 lumbar (lower back), 5 sacral (sacrum, fused) and 4 coccygeal vertebrae (fused). The lumbar vertebrae bear the most weight and are therefore the largest and strongest. Each vertebra has a vertebral body that absorbs pressure and a vertebral arch that protects the spinal cord.
Intervertebral discs
Between every two vertebrae sits an intervertebral disc: a resilient cushion with a tough outer ring (annulus fibrosus) and a soft core (nucleus pulposus). These discs absorb shocks, distribute pressure and enable movement. They are far stronger than most people assume, and they get stronger from being used: in regular runners the discs hold more water and are thicker than in people who do not exercise (Belavy et al., 2017). In a herniated disc the soft core bulges out, and in most people that shrinks back on its own.
Muscles and ligaments
A complex network of muscles and ligaments supports your spine. The deep stabilising muscles (multifidus, transversus abdominis) provide fine control, while the large muscles (erector spinae, latissimus dorsi) deliver strength and movement. Ligaments connect the vertebrae and limit excessive movement. This system is adaptive: it gets stronger through use and weaker through inactivity.
Nerves
The spinal cord runs through the spinal canal and branches at each vertebra into spinal nerves that send signals to and from the body. At the lumbar vertebrae, the spinal cord ends (at L1-L2) in a bundle of nerve roots called the cauda equina (horse tail). The sciatic nerve is the thickest nerve in the body and runs from the lower back via the buttock to the leg. Irritation of this nerve can cause radiating pain (sciatica).
Key message
Your back is strong, resilient and made to move. Most changes visible on a scan (such as mild disc degeneration or bulges) are normal and occur in people without pain. Like grey hair and wrinkles, they are signs of normal ageing, not damage.
Sources
The structure described on this page (33 vertebrae in five regions, and the spinal cord ending at L1-L2) is standard anatomy. We use a reference work for it rather than a study, because there is nothing here that research disagrees about: Anatomy, Back, Vertebral Column (StatPearls). That the discs respond well to loading comes from a study of runners: Belavy et al., Scientific Reports (2017).
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