Anatomy of the Spine

The spine, also known as the vertebral column or backbone, is a complex structure that plays a crucial role in supporting the body, allowing for movement, and protecting the spinal cord. It is composed of a series of bones called vertebrae, intervertebral discs, ligaments, muscles, nerves, and blood vessels.

The spine’s structure allows it to perform its functions effectively, but it can be affected by various conditions, including degenerative disc disease, herniated discs, spinal stenosis, scoliosis, and osteoporosis.

Vertebrae: The spine is made up of 33 vertebrae that are categorized into five regions: 7 cervical (neck), 12 thoracic (chest), 5 lumbar (lower back), 5 sacral (pelvic), and 4 coccygeal (tailbone). The sacral and coccygeal vertebrae are usually fused in adults. Each vertebra has a body (which bears weight), a vertebral arch (which forms the vertebral foramen, a hole for the spinal cord), and several processes for muscle and ligament attachments.

Intervertebral Discs: These are fibrocartilaginous cushions located between the bodies of adjacent vertebrae. Each disc has a tough outer layer (the annulus fibrosus) and a gel-like center (the nucleus pulposus). The discs act as shock absorbers and allow for movement between the vertebrae.

Ligaments and Muscles: Several ligaments and muscles are associated with the spine, providing stability and allowing for movements such as flexion, extension, lateral bending, and rotation. Key ligaments include the anterior and posterior longitudinal ligaments, the ligamentum flavum, and the interspinous and supraspinous ligaments. Major muscle groups include the erector spinae, the deep spinal muscles, and the abdominal muscles.

Spinal Cord and Nerves: The spinal cord runs through the vertebral foramen, protected by the vertebrae. It is part of the central nervous system and transmits signals between the brain and the rest of the body. Nerves exit the spinal cord through spaces between the vertebrae (intervertebral foramina) to innervate specific regions of the body.

Blood Supply: The spine and spinal cord receive blood from a network of arteries, including the vertebral, anterior spinal, and posterior spinal arteries, and blood is drained by a series of spinal veins.

Curvatures: The spine has four natural curves, which help to increase its strength, maintain balance in the upright position, absorb shock, and protect the spinal cord from injury. These are the cervical, thoracic, lumbar, and sacral curvatures.

1. Cervical Spine (Neck)
   • C1: Also known as the Atlas. It supports the skull and allows for the nodding motion of the head.
   • C2: Also known as the Axis. It allows for the rotation of the head.
   • C3-C7: These are the remaining cervical vertebrae. They provide support and structure for the neck and also have a role in neck movement.
2. Thoracic Spine (Upper Back)
   • T1-T12: These 12 thoracic vertebrae each articulate with a pair of ribs. They provide structure and support for the upper back.
3. Lumbar Spine (Lower Back)
   • L1-L5: These five vertebrae are larger because they carry more of the body’s weight. They provide structure and support for the lower back.
4. Sacral Spine (Pelvic Area)
   • S1-S5: These five sacral vertebrae are fused together to form the sacrum, which articulates with the hip bones to form the pelvis.
5. Coccyx (Tailbone)
   • This consists of usually four small, fused vertebrae at the base of the spine, forming the tailbone.

In total, the spine typically consists of 33 vertebrae, 24 of which are articulating (moving), and 9 of which are fused (in the sacrum and coccyx).