The human spinal column is divided into five sections: cervical (neck), thoracic (mid-back), lumbar (lower back), sacral, and coccygeal. Together, these regions contain 33 vertebrae, though several fuse into solid bone during development, leaving most adults with 24 individual movable vertebrae plus two fused bones at the base. Each section is shaped and sized differently to match the specific job it performs.
Cervical Spine: 7 Vertebrae (C1–C7)
The cervical region sits at the top of the spine and forms the structure of your neck. Its seven vertebrae are the smallest and most mobile in the entire column, allowing you to nod, tilt, and rotate your head. The first two vertebrae are unique. C1, called the atlas, is a ring-shaped bone that cradles the base of your skull and holds your head upright. C2, called the axis, has a bony peg that projects upward into the atlas, creating a pivot point that lets you turn your head side to side.
The cervical vertebrae also have a feature found nowhere else in the spine. Vertebrae C1 through C6 contain small holes in the bone that form a protective tunnel for the vertebral arteries, the blood vessels that supply the back of your brain. This combination of extreme mobility and critical blood supply is why neck injuries can be so serious.
The cervical spine curves gently inward toward the front of your body. This inward curve, called a lordotic curve, helps balance the weight of your head (roughly 10 to 12 pounds) over your torso.
Thoracic Spine: 12 Vertebrae (T1–T12)
The thoracic section makes up the longest stretch of the spine and runs through the mid-back. Each of its 12 vertebrae connects to a pair of ribs, forming the rigid cage that protects your heart and lungs. This rib attachment is the defining feature of the thoracic vertebrae. Small, flat connection points on each vertebra lock into matching surfaces on the ribs, and a single rib typically articulates with two neighboring vertebrae at once. For example, the fifth rib connects to both T4 and T5.
Because of this coupling with the rib cage, the thoracic spine sacrifices flexibility for stability. You can’t bend or twist your mid-back nearly as far as your neck or lower back. That trade-off is intentional: the thoracic region needs to stay relatively still so your rib cage can expand and contract smoothly during breathing. The thoracic spine curves gently outward (a kyphotic curve), giving the upper back its subtle rounded shape.
Lumbar Spine: 5 Vertebrae (L1–L5)
The five lumbar vertebrae in your lower back are the largest individual vertebrae in the spine, and they get progressively bigger as you move down. L5, the lowest, has the largest vertebral body and widest side projections of any vertebra in the entire column. This increasing size reflects increasing demand: the lumbar region bears the majority of your body’s weight and absorbs the compressive forces generated by lifting, bending, and standing.
The lumbar spine curves inward (lordotic), mirroring the cervical curve above. This inward sweep positions your center of gravity over your hips and lets you walk upright efficiently. The joint surfaces in this region are angled to favor forward and backward bending while limiting rotation, which is why twisting under load is a common mechanism for lower back injuries.
One important detail: the spinal cord itself does not extend the full length of the spine. It typically ends around the L1 vertebra, though this can range anywhere from the lower thoracic region to L3. Below that point, a bundle of individual nerve roots fans out through the remaining vertebral canal to reach the lower body.
Sacrum: 5 Fused Vertebrae
Below the lumbar spine, five sacral vertebrae gradually fuse into a single triangular bone called the sacrum. This fusion doesn’t happen all at once. The lower sacral segments begin fusing in the early teenage years, with most vertebrae showing bony fusion by around age 13 to 16. The junction between S1 and S2, however, is the slowest to finish. Most people don’t achieve complete fusion at that level until their mid-to-late twenties.
The sacrum sits like a wedge between the two hip bones, forming the back wall of the pelvis. It transfers the entire weight of your upper body into the pelvis and then into your legs. Its broad, flat shape and tight ligament connections to the hip bones make this joint extremely stable, though it does allow a small amount of movement that becomes important during childbirth.
Coccyx: 4 Fused Vertebrae
The coccyx, or tailbone, is the very bottom of the spinal column. It forms from four small vertebrae (occasionally three or five) that fuse into a single small bone. While often dismissed as a vestigial structure, the coccyx serves as an anchor point for muscles and ligaments of the pelvic floor. It also helps support your weight when you sit and lean back.
The Discs Between Vertebrae
Between each pair of movable vertebrae sits an intervertebral disc, a tough, flexible pad that acts as both a shock absorber and a spacer. Each disc has two parts: a firm outer ring of cartilage that holds everything together, and a gel-like center that cushions compressive forces. When the outer ring weakens or tears, the gel center can push outward, which is the basic mechanism behind a herniated disc. The sacrum and coccyx, being fused, have no discs between their segments.
How the Curves Work Together
Viewed from the side, a healthy spine forms an S-shaped series of four curves. The cervical and lumbar sections curve inward, while the thoracic and sacral sections curve outward. These alternating curves are not a flaw. They function like a spring, distributing mechanical stress and absorbing impact far more effectively than a straight column could. A perfectly straight spine would actually be less resilient and more prone to compression injuries.
The thoracic and sacral curves are called primary curves because they’re present at birth, shaped by fetal development. The cervical and lumbar curves are secondary curves that develop after birth as an infant learns to hold up its head and eventually walk. Together, these curves keep your head balanced directly over your pelvis, minimizing the muscular effort needed to stand upright.