Human Spine Anatomy: Vertebrae, Joints, and Curvatures

Posted on Jul 31, 2025 in Human Biology

Spine Anatomy Fundamentals

The spine supports the head and provides mobility to the vertebral column. It combines flexibility (vertebrae) and firmness (intervertebral discs). The vertebrae are larger towards the base of the spine, narrowing superiorly.

Physiological Curvatures of the Spine

The adult spine exhibits four physiological lateral curvatures:

  • Cervical Lordosis: An anterior convexity in the neck region.
  • Thoracic Kyphosis: An anterior concavity in the upper back.
  • Lumbar Lordosis: An anterior convexity in the lower back.
  • Sacrococcygeal Kyphosis: An anterior concavity in the sacral and coccygeal regions.

A newborn typically has a single spinal curve. An abnormal lateral curvature of the spine is known as scoliosis.

Intervertebral Foramina

These openings are located between the pedicles of two adjacent vertebrae, allowing spinal nerves to pass through. A disc herniation can compress these nerves, leading to pain or neurological symptoms.

Vertebrae Characteristics

Cervical Vertebrae (C1-C7)

  • Body: Small and rectangular.
  • Vertebral Foramen: Large and triangular.
  • Transverse Processes: Contain a foramen (foramen transversarium) for the vertebral artery (except C7).
  • Spinous Process: Often bituberculate (bifid), especially C2-C6.

Thoracic Vertebrae (T1-T12)

  • Body: Intermediate size, heart-shaped.
  • Vertebral Foramen: Intermediate size, rounded.
  • Transverse Processes: Possess articular facets for the tubercles of ribs (T1-T10).
  • Spinous Process: Long, slender, and pointed, projecting inferiorly.

Lumbar Vertebrae (L1-L5)

  • Body: Large, kidney-shaped.
  • Vertebral Foramen: Small and triangular.
  • Transverse Processes: Large, costiform (rib-like).
  • Spinous Process: Short, thick, horizontal, and quadrilateral.

Specialized Vertebrae

Atlas (C1)

The Atlas is characterized by:

  • A large vertebral foramen.
  • Anterior Arch: Features an anterior tubercle and an anterior facet for the dens of the axis.
  • Posterior Arch: Features a posterior tubercle and a groove for the vertebral artery.
  • Lateral Masses: Bear superior articular facets for the occipital condyles and inferior articular surfaces for the axis.

Axis (C2)

The Axis is distinguished by its dens (odontoid process), which articulates with the atlas via three facets.

Sacrum

The sacrum features:

  • Anterior Surface: Displays transverse lines and the sacral promontory, which forms the lumbosacral joint surface.
  • Apex: Articulates with the coccyx.
  • Lateral Masses (Alae): Form the “wings” anteriorly and the sacroiliac joint facets posteriorly.
  • Posterior Surface: Includes the median sacral crest, lateral sacral crests, and eight sacral foramina (four anterior, four posterior).
  • Sacral Canal: Runs through the sacrum.
  • Sacral Hiatus: Located posteriorly at the inferior end.

Coccyx

The coccyx is typically formed by the fusion of four coccygeal vertebrae.

Spinal Joints and Articulations

Atlanto-Occipital Joint

  • Type: Condyloid joint.
  • Articular Surfaces: Occipital condyles articulate with the superior articular fossae of the atlas’s lateral masses.
  • Reinforcements: Anterior and posterior atlanto-occipital membranes.
  • Movements: Flexion, extension, and lateral bending (e.g., nodding “yes”).

Atlanto-Axial Joint

  • Type: Pivot (trochoid) and plane (arthrodial) joints.
  • Articular Surfaces:
    • The facet of the dens articulates with the anterior arch of the atlas.
    • The inferior articular facets of the atlas’s lateral masses articulate with the superior articular facets of the axis.
  • Reinforcements: Cruciate ligament, apical ligament of the dens, alar ligaments, and tectorial membrane.
  • Movements: Rotation (e.g., shaking “no”) and gliding.

Intervertebral Joints

These include:

  • Intervertebral Discs: Amphiarthrosis (symphysis) joints between vertebral bodies.
  • Facet (Zygapophyseal) Joints: Plane (arthrodial) joints between articular processes.

Orientation of Articular Facets:

  • Cervical Region: Approximately 45-degree angle; superior facets face upward and backward, inferior facets face downward and forward.
  • Thoracic Region: More vertically oriented.
  • Lumbar Region: Superior concave facets face medially and backward.

Key Spinal Ligaments:

Ligaments that attach to each other all the vertebrae include:

  • Anterior Longitudinal Ligament: Connects the anterior surfaces of vertebral bodies.
  • Posterior Longitudinal Ligament: Connects the posterior surfaces of vertebral bodies.
  • Ligamenta Flava (Yellow Ligaments): Connect adjacent vertebral laminae.
  • Supraspinous Ligament: Connects the tips of spinous processes.

Overall Spinal Movements:

The vertebral column as a whole allows for:

  • Flexion
  • Extension
  • Lateral Bending
  • Rotation around its axis

Sacroiliac Joint

  • Type: Diarthro-amphiarthrosis (partially synovial, partially fibrous).
  • Articular Surfaces: Ear-shaped auricular surfaces on the posterior ilium and lateral sacral masses.
  • Reinforcing Ligaments:
    • Anterior and posterior sacroiliac ligaments.
    • Sacrospinous and sacrotuberous ligaments.
    • Superior and inferior iliolumbar ligaments.
  • Movements: Limited movement, primarily during childbirth to allow slight anterior tilting of the sacrum and posterior movement of the coccyx.

Key Bony Landmarks and Vertebral Levels

  • Oropharynx: C2
  • Glottis: C4
  • Heart: T6-T8
  • Kidney: T12-L2
  • Pancreas: L1-L2
  • Tracheal Bifurcation (Carina): T4
  • Aortic Arch (highest point): T4
  • Carotid Artery Bifurcation: C3
  • Superior Border of Sternum (Manubrium): T2