Vertebral Anatomy

Spinal regions and spinal cord topography

The vertebral column is formed by vertebrae from several regions: cervical, thoracic, lumbar, as well as the fused vertebrae of the sacrum and coccyx. The spinal cord lies inside the vertebral canal. It is covered by the pia mater and arachnoid mater, between which lies the subarachnoid space containing 120–140 ml of cerebrospinal fluid (CSF). Within the dural sac, the spinal cord is "suspended" by the denticulate ligaments and is also fixed by nerve roots and adipose tissue.

The spinal cord is divided into segments: cervical (C1–C8), thoracic (Th1–Th12), lumbar (L1–L5), sacral (S1–S5), and coccygeal (Co1–Co3). It is important to understand that the level of the spinal cord segments does not correspond to the level of the vertebrae of the same name. This relationship is called skeletotopy:

• Upper cervical segments lie at the level of the bodies of their corresponding vertebrae.
• Lower cervical and upper thoracic segments lie 1 vertebra higher.
• Mid-thoracic segments lie 2 vertebrae higher.
• Lower thoracic segments lie 3 vertebrae higher.
• Lumbar segments project onto the bodies of the Th10–Th11 vertebrae.
• Sacral and coccygeal segments are located at the level of the Th12–L1 vertebrae. This is precisely where the conus medullaris is located, formed by the S3–S5 and coccygeal segments.

Supporting structures and spinal stability

To assess spinal stability in trauma, it is divided into three supporting complexes. Damage to these structures determines the severity of the patient's condition.

1. Anterior supporting complex: includes the anterior longitudinal ligament, the anterior part of the intervertebral discs (annulus fibrosus), and the anterior half of the vertebral bodies.
2. Middle supporting complex: consists of the posterior longitudinal ligament, the posterior part of the intervertebral discs (annulus fibrosus), and the posterior half of the vertebral bodies.
3. Posterior supporting complex: formed by the vertebral arches, articular capsules, as well as the ligamentum flavum, interspinous, and supraspinous ligaments.

Spinal injuries are classified by anatomical location (cervical, thoracic, lumbar, sacrum, and coccyx) and by the presence of neurological deficit. Uncomplicated injuries affect only the vertebrae and ligaments, while complicated injuries are accompanied by damage to the spinal cord and nerve roots. If the integrity of the ligamentous complex is compromised and there is a tendency for vertebral displacement with the risk of spinal cord compression, such an injury is termed unstable.

Anatomy of spinal nerves and roots

Within the vertebral canal, the fibers of the anterior (motor) and posterior (sensory) roots merge. This results in the formation of 31 pairs of spinal nerves. The topography of their exit follows strict patterns:

• There are 7 vertebrae in the cervical region, but 8 pairs of nerves. The C1 nerve exits above the first cervical vertebra (between the occipital bone and the atlas). The C2–C7 nerves also exit above their corresponding vertebrae. However, the C8 nerve emerges between the seventh cervical (C7) and first thoracic (Th1) vertebrae.
• In the thoracic (12 pairs), lumbar (5 pairs), and sacral (5 pairs) regions, each nerve exits the vertebral canal strictly below the correspondingly numbered vertebra.
• In the coccygeal region, there is 1 pair (sometimes more) of nerves.

Just proximal to the point where the roots merge, a thickening—the spinal ganglion (dorsal root ganglion)—is located on the posterior root. It contains pseudounipolar neurons. A single process emerges from the cell body and immediately divides in a T-shape into a peripheral process (running to receptors) and a central process (heading to the CNS).

Fiber organization and diagnostic imaging

Afferent fibers in the posterior root are strictly organized in space:

• Medial part: the thickest myelinated fibers from muscle spindles (responsible for proprioceptive sensitivity).
• Central part: fibers from touch, pressure, and vibration receptors (discriminative sensitivity).
• Lateral part: thin unmyelinated fibers (protopathic pain and temperature sensitivity).

To visualize spinal structures in patients presenting with pain, lateral radiography is used (for the cervical, thoracic, and lumbar regions). This makes it possible to assess the degree of structural damage to the vertebrae and diagnose specific pathologies, such as psoriatic arthritis.

Class and exam questions

What else to study on this topic

• Anatomical terminology, body planes, and axes.
• General structure of a typical vertebra (body, arch, processes).
• Age-related features of the structure of the vertebral column.
• Spinal meninges and fixation in the vertebral canal.
• Radiography of the pelvis, hands, and feet in joint pathology.

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.