General structure and elements of a vertebra
The vertebral column (columna vertebralis) is formed by sequentially connected vertebrae. A typical vertebra consists of three main components:
- Body (corpus vertebrae) — the massive, thickened anterior part. It has superior and inferior surfaces, as well as nutrient foramina (foramina nutricia). The bodies are connected to each other by intervertebral discs.
- Arch (arcus vertebrae) — located posteriorly and, together with the body, bounds the vertebral foramen (foramen vertebrale). The combination of these foramina forms the vertebral canal (canalis vertebralis). The arch includes pedicles (pediculus) and laminae (lamina). It features superior and inferior vertebral notches, which form the intervertebral foramen (foramen intervertebrale) when adjacent vertebrae articulate.
- Processes (processus) — there are seven in total. These include one unpaired spinous process, a pair of transverse processes, and two pairs of superior and inferior articular processes with articular surfaces.
Joints between vertebral bodies
The articulations of the vertebral bodies are classified as intervertebral symphyses (symphysis intervertebralis) — cartilaginous joints that provide shock absorption, even pressure distribution, and slight mobility.
The main element of the symphysis is the intervertebral disc (discus intervertebralis), which is attached to the hyaline cartilaginous plates of the vertebral bodies. The structure of the disc comprises:
- Anulus fibrosus (anulus fibrosus) — formed by concentric layers of fibrocartilage.
- Nucleus pulposus (nucleus pulposus) — located in the center, it is a remnant of the embryonic notochord.
The thickness of the discs varies depending on the region. In the cervical region, they are thickest relative to the vertebral body; in the thoracic region, they are thinner; and in the lumbar region, the discs are the most massive. In the sacral region, the intervertebral discs eventually calcify, and the joints transition into bone fusions — synostoses.
Ligamentous apparatus of vertebral bodies
The vertebral bodies are securely fixed by two strong longitudinal ligaments:
- Anterior longitudinal ligament (lig. longitudinale anterius) — descends from the anterior tubercle of the atlas (base of the skull) all the way down to the pelvis. It firmly fuses with the intervertebral discs and vertebral bodies. Its main biomechanical function is to prevent hyperextension of the vertebral column.
- Posterior longitudinal ligament (lig. longitudinale posterius) — runs along the posterior surface of the vertebral bodies inside the vertebral canal. It prevents excessive flexion of the spine.
At the level between the sacrum and the coccyx, these longitudinal structures continue as the anterior and posterior sacrococcygeal ligaments (ligg. sacrococcygea).
Ligaments of the arches and processes
The vertebral arches and processes are reinforced by a complex system of ligaments:
- Ligamenta flava (ligg. flava) — span between the arches of adjacent vertebrae. They owe their name to the elastic fibers of which they are composed. These ligaments play a crucial role in maintaining vertical posture of the trunk.
- Interspinal ligaments (ligg. interspinalia) — connect adjacent spinous processes.
- Supraspinous ligament (lig. supraspinale) — runs as a continuous cord along the tips of the spinous processes from the 7th cervical vertebra to the sacrum. In the cervical region, it broadens to become the ligamentum nuchae (lig. nuchae), which extends from the external occipital protuberance to the spinous processes of the cervical vertebrae.
- Intertransverse ligaments (ligg. intertransversaria) — fix adjacent transverse processes.
Zygapophysial joints
Zygapophysial joints (articulationes zygapophysiales) are formed between the superior and inferior articular processes. These are true synovial joints with a thin capsule attached strictly along the margins of the articular surfaces.
The shape of the articular surfaces and the range of motion strictly depend on the region of the spine:
- Cervical region — surfaces are flat, providing maximum flexibility.
- Thoracic region — articular facets have a frontal orientation. This anatomy significantly restricts flexion and extension in this segment.
- Lumbar region — surfaces are located in the sagittal plane. This allows for flexion and extension while severely restricting rotation.
Briefly: answers to topical questions
Which ligaments reinforce the sacrococcygeal articulation?
The sacrococcygeal articulation is reinforced by the anterior and posterior sacrococcygeal ligaments (ligg. sacrococcygea), which are a continuation of the longitudinal ligaments of the spine between the sacrum and the coccyx.
What structures form the anterior, posterior, and lateral walls of the vertebral canal?
The vertebral canal is formed by sequentially arranged vertebral foramina. The vertebral arch bounds the vertebral foramen posteriorly, and the pedicles and other arch elements contribute to bounding the canal laterally. The ligamenta flava connect the vertebral arches and form the posterior wall of the vertebral canal.
What types of movements (around which axes) are possible in the vertebral column as a whole?
The following movements are possible in the vertebral column: around the frontal axis — flexion and extension; around the vertical axis — rotation; around the sagittal axis — abduction and adduction. In the lumbar region, the joints allow flexion and extension and restrict rotation; in the thoracic region, flexion and extension are restricted.
What type of joints, according to surface shape and number of axes, are the zygapophysial joints?
Zygapophysial joints (articulationes zygapophysiales) are classified as synovial joints. In the cervical region they are flat, in the thoracic region they are oriented in the frontal plane, and in the lumbar region — in the sagittal plane. In the lumbar region, the inferior articular facets are convex, and the superior ones are concave. The number of axes is not specified in the cited sources.
How are the atlanto-occipital and atlantoaxial joints structured and classified?
These joints have different structures and belong to different biomechanical types.
- Atlanto-occipital joint (articulatio atlantooccipitalis) — formed by the occipital condyles and the superior articular surfaces of the atlas. It is a paired, condylar (ellipsoid), biaxial joint.
- Atlantoaxial joints — are compound joints, as movements in them occur simultaneously. These include the median atlantoaxial joint, which by shape is classified as a uniaxial pivot joint (articulatio trochoidea) and provides rotation around the vertical axis.
Class and exam questions
Which structure prevents excessive hyperextension of the spine?
Hyperextension is restricted by the anterior longitudinal ligament, which runs from the base of the skull to the pelvis and is firmly fused with the vertebral bodies and intervertebral discs.
How do the ligamenta flava maintain the vertical posture of the torso?
They consist of elastic fibers (which gives them their yellow color) that act as resilient bands, returning the spine to its original position after flexion.
Why are the vertebrae immobile in the sacral region?
In the sacral region, the intervertebral discs calcify during development, and the vertebral joints transition into immobile synostoses (bone fusions).
How does the orientation of articular surfaces affect lumbar mobility?
In the lumbar region, the zygapophysial joints have a sagittal orientation. This allows for free flexion and extension, but reliably blocks trunk rotation.
What else to study on this topic
- Topography and boundaries of the intervertebral foramen
- Histological structure of the intervertebral disc and notochord remnant
- Formation of the vertebral canal and its contents
- Transition of the supraspinous ligament into the ligamentum nuchae in the neck
- Age-related changes in joints: synostosis of the sacral vertebrae
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