Axial Skeleton: Vertebral Column, Abnormal Curvatures, Spina Bifida, and Bony Thorax

Chapter 7: Axial Skeleton – Part 2

Overview

This section covers the anatomy and physiology of the vertebral column, abnormal spinal curvatures, the condition of spina bifida, and the structure of the bony thorax. Understanding these components is essential for comprehending the support, protection, and movement functions of the axial skeleton.

Vertebral Column

Structure and Function

The vertebral column is a flexible, curved structure that extends from the skull to the pelvis, providing the main support for the body and protecting the spinal cord.

• Composition: Consists of 26 vertebrae in adults (7 cervical, 12 thoracic, 5 lumbar, 1 sacrum [5 fused], 1 coccyx [4 fused]).

• Functions:

  • Protects the spinal cord

  • Serves as attachment points for ribs and back musculature

  • Intervertebral discs provide shock absorption between vertebrae

• Length: Male ≈ 28 in; Female ≈ 24 in

Regions of the Vertebral Column

• Cervical Vertebrae (C1–C7): C1 is the Atlas, C2 is the Axis

• Thoracic Vertebrae (T1–T12): Articulate with ribs

• Lumbar Vertebrae (L1–L5): Largest and strongest

• Sacrum: 5 fused bones, forms the posterior wall of the pelvis

• Coccyx: 4 fused bones, forms the tailbone

Structure of a Typical Vertebra

• Vertebral body (centrum): Main weight-bearing region

• Lamina: Forms the vertebral arch

• Vertebral foramen: Canal for the spinal cord

• Spinous process: Posterior projection for muscle attachment

• Transverse process: Lateral projections for muscle and ligament attachment

Features of Cervical, Thoracic, and Lumbar Vertebrae

• Cervical: Thinner, delicate, with transverse foramina

• Thoracic: Thicker, heart-shaped body, facets for rib articulation

• Lumbar: Thickest, large kidney-shaped body, robust processes

Normal and Abnormal Spinal Curvatures

Normal Curvatures

The adult vertebral column has an S-shaped curve with four main curvatures:

• Cervical curvature: Develops as infants lift their heads

• Thoracic curvature: Present at birth

• Lumbar curvature: Develops as children begin to walk

• Sacral curvature: Present at birth

Abnormal Curvatures

Abnormal spinal curvatures can result from congenital defects, disease, or injury.

• Scoliosis: Lateral curvature, often with shoulder or hip asymmetry. Causes include congenital defects, muscle paralysis, or leg length discrepancy.

• Kyphosis: Exaggeration of the thoracic curve, producing a "hunchback" appearance. Common in elderly due to osteoporosis or vertebral disc degeneration.

• Lordosis: Exaggeration of the lumbar curve, producing a "hollow back." Seen in pregnancy, obesity, or rickets (vitamin D deficiency).

Spina Bifida

Definition and Types

Spina bifida is a neural tube defect resulting from incomplete closure of the vertebral arch during embryonic development, often affecting the lumbar and sacral regions.

• Spina bifida occulta: Mildest form; may present as a tuft of hair or dimple. Usually no neurological problems.

• Meningocele: Meninges protrude through the defect, forming a sac filled with fluid. Risk of infection and rupture.

• Myelomeningocele: Most severe; spinal cord and nerves protrude into the sac, leading to loss of lower limb function, bladder, and bowel control.

Causes and Prevention

• Associated with low maternal folic acid levels during pregnancy

• Prevention: Adequate intake of folic acid (leafy greens, spinach, cooked fruits)

Diagnosis and Treatment

• Maternal blood tests for elevated alpha-fetoprotein

• Amniocentesis and imaging (spinal ultrasonography)

• Surgical procedures to close the defect

Bony Thorax

Structure and Function

The bony thorax (thoracic cage) protects vital organs such as the heart and lungs and provides attachment points for muscles involved in respiration.

• Sternum: Composed of the manubrium, body, and xiphoid process

• Ribs: 12 pairs, classified as true, false, or floating

Classification of Ribs

Type	Number	Attachment
True Ribs (Vertebrosternal)	1–7	Directly attached to sternum via costal cartilage
False Ribs (Vertebrochondral)	8–10	Indirectly attached to sternum via cartilage of rib 7
Floating Ribs (Vertebral)	11–12	No anterior attachment

Clinical Relevance

• Rib fractures can puncture major organs (heart, lungs, spleen, liver) and blood vessels

• Most common at points of greatest force or curvature

Summary Table: Vertebral Column Regions

Region	Vertebrae	Key Features
Cervical	C1–C7	Atlas (C1), Axis (C2), transverse foramina
Thoracic	T1–T12	Facets for rib articulation
Lumbar	L1–L5	Large, robust bodies
Sacrum	S1–S5 (fused)	Forms posterior pelvis
Coccyx	Co1–Co4 (fused)	Tailbone

Additional info:

• Intervertebral discs are composed of fibrocartilage and act as shock absorbers.

• Spinal curvatures are essential for balance and weight distribution.

• Spina bifida is best prevented by folic acid supplementation before and during early pregnancy.