7.3 The Vertebral Column

The vertebral column is a marvel of human anatomy, supporting our entire body and protecting the spinal cord. It's divided into five regions: cervical, thoracic, lumbar, sacral, and coccygeal, each with unique characteristics that allow for different functions and movements.

Our spine isn't just a straight line - it has curves that develop as we grow. These curves help us absorb shock, maintain balance, and distribute weight effectively. The vertebrae themselves have specific features that vary by region, working together with intervertebral discs and ligaments to keep us upright and flexible.

Vertebral Column Anatomy

Regions of vertebral column

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• Cervical region contains 7 cervical vertebrae (C1-C7) forms the neck and supports the skull
• Thoracic region includes 12 thoracic vertebrae (T1-T12) connects to the ribs and forms the upper back
• Lumbar region has 5 lumbar vertebrae (L1-L5) bears the weight of the upper body and allows for significant flexion and extension
• Sacral region consists of 1 sacrum, formed by the fusion of 5 sacral vertebrae (S1-S5), connects the spine to the hip bones
• Coccygeal region includes 1 coccyx, made up of 3-5 fused coccygeal vertebrae, serves as an attachment point for pelvic floor muscles

Spinal curvatures from birth to adulthood

• Primary curves are present at birth
  • Thoracic curve is concave anteriorly and allows space for the heart and lungs
  • Sacral curve is concave anteriorly and provides stability for upright posture
• Secondary curves develop during infancy and childhood
  • Cervical curve becomes convex anteriorly as an infant begins to hold their head up (around 3 months)
  • Lumbar curve becomes convex anteriorly as a child starts to walk (around 12-18 months)
• Spinal curves increase flexibility, absorb shock, distribute mechanical stress, and maintain balance and upright posture

Vertebral Structure and Function

Vertebrae features across spinal regions

• Cervical vertebrae are the smallest and lightest, have transverse foramina for vertebral arteries, and bifid spinous processes (except C7)
  • C1 (atlas) lacks a body and spinous process and articulates with the skull
  • C2 (axis) has the dens (odontoid process) that pivots within C1 to allow for rotation of the head
• Thoracic vertebrae are intermediate in size, have long, slender spinous processes angled inferiorly, and costal facets for rib articulation
• Lumbar vertebrae are the largest and most massive, have short, thick, rectangular spinous processes, and lack transverse foramina and costal facets
• Sacrum is triangular-shaped, formed by the fusion of 5 sacral vertebrae, and has sacral foramina for spinal nerve passage
• Coccyx is a small, triangular bone formed by the fusion of 3-5 coccygeal vertebrae and serves as an attachment site for pelvic floor muscles

Composition of intervertebral discs

• Annulus fibrosus is the tough, outer ring composed of concentric layers of fibrocartilage with collagen fibers arranged in alternating directions for strength
• Nucleus pulposus is the gelatinous core with a high water content that absorbs compressive forces
• Intervertebral discs allow for flexibility, act as shock absorbers, maintain separation between vertebral bodies, and prevent nerve compression and excessive wear

Ligaments supporting vertebral column

• Anterior longitudinal ligament runs along the anterior surface of vertebral bodies and limits hyperextension
• Posterior longitudinal ligament runs along the posterior surface of vertebral bodies within the vertebral canal and limits hyperflexion
• Ligamentum flavum connects the laminae of adjacent vertebrae, is highly elastic, and aids in maintaining upright posture
• Interspinous ligaments connect the spinous processes of adjacent vertebrae and limit flexion
• Supraspinous ligament connects the tips of the spinous processes from C7 to the sacrum and limits flexion
• Intertransverse ligaments connect the transverse processes of adjacent vertebrae and limit lateral flexion

Vertebral Components and Associated Structures

• Vertebral body: The main weight-bearing portion of the vertebra
• Vertebral arch: Forms the posterior portion of the vertebra, enclosing the spinal cord
• Facet joints: Allow for movement between adjacent vertebrae and guide spinal motion
• Spinal cord: Passes through the vertebral canal formed by the vertebral arches
• Spinal nerves: Exit through intervertebral foramina, transmitting signals between the spinal cord and body