Overview
This section covers the anatomy of the vertebral column, including its regions, curvatures, structural features, common disorders, intervertebral discs, and supporting ligaments.
Regions and Structure of the Vertebral Column
- The vertebral column, also called the spinal column or spine, is made up of 24 individual vertebrae, plus the sacrum and coccyx.
- It is divided into five regions:
- 7 cervical vertebrae (C1–C7) in the neck
- 12 thoracic vertebrae (T1–T12) in the upper back
- 5 lumbar vertebrae (L1–L5) in the lower back
- The sacrum, formed by the fusion of 5 sacral vertebrae (part of the pelvis)
- The coccyx, or tailbone, formed by the fusion of 4 small coccygeal vertebrae
- The vertebral column originally develops as 33 vertebrae, but fusions reduce this number in adulthood.
- Vertebral bodies increase in size from the cervical to the lumbar region to support increasing body weight.
- The vertebral column supports the head, neck, and body, allows movement, and protects the spinal cord, which passes through the vertebral foramina.
Curvatures and Disorders
- The adult vertebral column has four curvatures:
- Two primary curves: thoracic and sacrococcygeal (retained from fetal development)
- Two secondary curves: cervical and lumbar (develop after birth as a child learns to hold up the head, sit, stand, and walk)
- Curvatures increase the strength, flexibility, and shock-absorbing ability of the spine. They deepen with increased load and return when the load is removed.
- Disorders of spinal curvature include:
- Kyphosis: excessive posterior curvature of the thoracic region (humpback); often due to osteoporosis weakening the anterior vertebrae.
- Lordosis: excessive anterior curvature of the lumbar region (swayback); commonly associated with obesity or late pregnancy.
- Scoliosis: abnormal lateral curvature with twisting of the vertebral column; most common in girls, often with unknown cause, and may worsen during adolescent growth spurts.
- Abnormal curvatures can be detected by observing the spine from the side and back, and by having the person bend forward.
General Vertebra Structure
- A typical vertebra consists of:
- A body (anterior, weight-bearing portion)
- A vertebral arch (formed by right and left pedicles and laminae)
- Seven processes: two transverse (lateral), one spinous (posterior), two superior articular, and two inferior articular processes
- The vertebral foramen (opening between the body and arch) houses the spinal cord; aligned vertebral foramina form the vertebral (spinal) canal.
- Intervertebral foramina, formed by notches in adjacent pedicles, allow spinal nerves to exit the column.
- The transverse and spinous processes serve as muscle attachment sites.
- Articular processes form joints between adjacent vertebrae, with their orientation influencing movement in each region.
Regional Vertebral Modifications
- Cervical Vertebrae:
- Small body, bifid (Y-shaped) spinous process (except C7, which is longer and prominent)
- Transverse processes are U-shaped and contain a transverse foramen for arteries supplying the brain
- C1 (atlas): ring-shaped, lacks body and spinous process, supports the skull, has elongated transverse processes
- C2 (axis): has the dens (odontoid process) projecting upward, allowing head rotation
- Thoracic Vertebrae:
- Larger body than cervical vertebrae
- Long, downward-angled spinous process overlapping the next vertebra
- Costal facets on the body and transverse process for rib attachment
- Superior articular processes face anteriorly; inferior face posteriorly
- Lumbar Vertebrae:
- Largest and thickest bodies to support the most weight
- Short, blunt spinous processes projecting posteriorly
- Short transverse processes; superior articular processes face backward, inferior face forward
- Sacrum:
- Triangular bone formed by fusion of five sacral vertebrae (fusion begins after age 20)
- Superior base is wide and weight-bearing; tapers to a non-weight-bearing apex
- Features include transverse ridges (fusion lines), median and lateral sacral crests, sacral promontory, auricular surface (articulates with ilium), sacral canal, sacral hiatus, and sacral foramina for nerve passage
- Superior articular processes articulate with L5 vertebra
- Coccyx:
- Formed by fusion of four small coccygeal vertebrae
- Articulates with the sacrum; not weight-bearing when standing, but may bear weight when sitting
Intervertebral Discs and Ligaments
- Intervertebral Discs:
- Fibrocartilaginous pads between vertebral bodies, providing cushioning and allowing movement
- Each disc has:
- Anulus fibrosus: tough, fibrous outer ring anchored to vertebral bodies
- Nucleus pulposus: soft, gel-like center with high water content for shock absorption
- Discs are thinnest in the cervical region and thickest in the lumbar region; they account for about 25% of the height between the pelvis and skull
- With age, the nucleus pulposus loses water, reducing disc height and flexibility
- Herniated disc: nucleus pulposus protrudes through a weakened anulus fibrosus, often compressing a spinal nerve and causing pain or muscle weakness (common at L4/L5, L5/S1, C5/C6, C6/C7)
- Ligaments of the Vertebral Column:
- Ligaments run along the length of the column, providing support and limiting excessive movement
- Anterior longitudinal ligament: runs along the anterior vertebral bodies, resists backward bending (important in preventing whiplash)
- Posterior longitudinal ligament: runs along the posterior vertebral bodies, inside the vertebral canal
- Supraspinous ligament: connects spinous processes of thoracic and lumbar vertebrae, resists forward bending
- Nuchal ligament: expanded supraspinous ligament in the cervical region, supports the skull and limits forward bending
- Ligamentum flavum: elastic ligaments connecting laminae of adjacent vertebrae, providing stretch and recoil during movement
Key Terms & Definitions
- Vertebral column: flexible column of vertebrae protecting the spinal cord and supporting the body
- Primary curvature: thoracic and sacrococcygeal curves present from fetal development
- Secondary curvature: cervical and lumbar curves developing after birth
- Kyphosis: excessive posterior curvature of the thoracic region
- Lordosis: excessive anterior curvature of the lumbar region
- Scoliosis: abnormal lateral and twisting curvature of the spine
- Intervertebral disc: fibrocartilaginous pad between vertebrae, with anulus fibrosus and nucleus pulposus
- Herniated disc: protrusion of the nucleus pulposus through the anulus fibrosus, compressing a spinal nerve
Action Items / Next Steps
- Review labeled diagrams of vertebral regions, typical vertebra features, and abnormal curvatures.
- Watch assigned videos on osteoporosis and herniated discs to understand their effects on the vertebral column.
- Use interactive tools to identify bones, intervertebral discs, and ligaments of the vertebral column.
- Study the structural differences among cervical, thoracic, lumbar, sacral, and coccygeal vertebrae for identification and understanding of function.