The Vertebral Column: Structure and Function

General Characteristics

The vertebral column, also known as the spine or spinal column, is a flexible, curved structure that extends from the skull to the pelvis. It serves several essential functions in the human body:

• Transmit weight of the trunk to the lower limbs

• Surround and protect the spinal cord

• Provide attachment points for ribs and muscles

The adult vertebral column contains 26 irregular bones called vertebrae, organized into five major regions. In infants, there are 33 vertebrae, some of which fuse during development.

Regions of the Vertebral Column

The vertebral column is approximately 28 inches long and is divided into five major regions:

• Cervical: 7 vertebrae (C1–C7)

• Thoracic: 12 vertebrae (T1–T12)

• Lumbar: 5 vertebrae (L1–L5)

• Sacrum: 1 bone formed from the fusion of 5 vertebrae; articulates with the hip

• Coccyx: 4 fused bones; forms the terminus of the column

Mnemonic: Remember meal times—7 am (cervical), 12 noon (thoracic), and 5 pm (lumbar).

Curvatures of the Vertebral Column

The vertebral column has four main curvatures that increase its resilience and flexibility:

• Cervical and lumbar curvatures: Concave posteriorly

• Thoracic and sacral curvatures: Convex posteriorly

These curvatures help distribute mechanical stress during movement and standing.

Clinical Considerations: Abnormal Spinal Curvatures

Types of Abnormal Curvatures

Abnormal spinal curvatures may be congenital or result from disease, poor posture, or unequal muscle pull. The main types include:

• Scoliosis: Abnormal lateral rotation of the spine, most often in the thoracic region; may cause breathing difficulties.

• Kyphosis (hunchback): Abnormal dorsal thoracic curvature; common in osteoporosis, tuberculosis, rickets, or osteomalacia.

• Lordosis (swayback): Accentuation of lumbar curvature; seen in disease, males with pot bellies, and pregnant females.

Ligaments and Intervertebral Discs

Ligaments Supporting the Vertebral Column

Ligaments, along with trunk muscles, help support the vertebral column:

• Anterior and posterior longitudinal ligaments: Continuous bands from neck to sacrum; prevent hyperextension and hyperflexion.

• Ligamentum flavum: Connects adjacent vertebrae.

• Short ligaments: Connect each vertebra to those above and below.

Intervertebral Discs

Intervertebral discs are cushion-like pads between vertebrae that act as shock absorbers. Each disc consists of two parts:

• Nucleus pulposus: Inner gelatinous nucleus; provides elasticity and compressibility.

• Anulus fibrosus: Outer collar of collagen and fibrocartilage; limits expansion of nucleus pulposus when compressed.

Clinical: Herniated (Prolapsed) Discs

Severe trauma may cause rupture of the anulus fibrosus, resulting in protrusion of the nucleus pulposus. This can press on the spinal cord or nerves, causing pain or numbness. Treatment options include exercise, massage, heat, painkillers, or surgery.

Structure of a Typical Vertebra

General Structure

All vertebrae share a common structural pattern:

• Body: Anterior weight-bearing region

• Vertebral arch: Composed of two pedicles (sides) and two laminae (posterior plates)

• Vertebral foramen: Enclosure formed by body and arch

• Vertebral canal: Series of vertebral foramina

• Intervertebral foramina: Lateral openings for spinal nerves

Processes of Vertebrae

Each vertebra has seven processes:

• Spinous process: Projects posteriorly

• Transverse processes (2): Project laterally

• Superior articular processes (2): Protrude superiorly

• Inferior articular processes (2): Protrude inferiorly

Regional Vertebral Characteristics

Cervical Vertebrae (C1–C7)

The cervical vertebrae are the smallest and lightest. Key features include:

• Oval-shaped body

• Bifid spinous processes (except C7)

• Large, triangular vertebral foramen

• Transverse foramen in each transverse process for artery passageways

• C7 is vertebra prominens, palpable through the skin

Atlas (C1): No body or spinous process; articulates with occipital condyles for nodding "Yes".

Axis (C2): Has a knoblike dens projecting superiorly; allows rotation for saying "No".

Thoracic Vertebrae (T1–T12)

Thoracic vertebrae increase in size and articulate with ribs. Unique features:

• Heart-shaped body with two small demifacets for rib articulation

• Circular vertebral foramen

• Long, sharp spinous process pointing inferiorly

• Transverse costal facets for rib articulation (except T11, T12)

• Articular facet orientation allows rotation

Lumbar Vertebrae (L1–L5)

The lumbar vertebrae are located in the "small of the back" and receive the most stress. Features include:

• Massive, kidney-shaped bodies

• Short, thick pedicles and laminae

• Flat, hatchet-shaped spinous processes pointing posteriorly

• Triangular vertebral foramen

• Articular facet orientation locks vertebrae together, preventing rotation

Comparison Table: Regional Characteristics of Cervical, Thoracic, and Lumbar Vertebrae

Sacrum and Coccyx

Sacrum

The sacrum is a triangular bone forming the posterior wall of the pelvis, made from five fused vertebrae (S1–S5). It articulates with the coccyx inferiorly and hip bones laterally via auricular surfaces, forming sacroiliac joints. Key features:

• Sacral promontory: Anterosuperior margin

• Transverse ridges: Lines of fusion

• Anterior and posterior sacral foramina: Openings for nerves and vessels

• Alae: Winglike expansions

• Median and lateral sacral crests: Roughened areas on posterior side

• Sacral canal: Continuation of vertebral canal

• Sacral hiatus: Large opening at end of canal

Coccyx

The coccyx, or tailbone, is formed from three to five fused vertebrae and articulates superiorly with the sacrum. It has very little function in humans.