VERTEBRAL COLUMN

I. VERTEBRAL COLUMN ‑ functions to support weight of body and protect spinal cord while permitting movements of trunk and providing for muscle attachments.

A. Typical vertebra (Atlas Fig. 4.4; Dissector Fig. 4.3; Snell Fig. 12‑2B)

1. A typical vertebra (by convention thoracic or upper lumbar) consists of a body (anterior) and a vertebral arch (posterior) surrounding the vertebral canal (houses spinal cord).

2. The vertebral arch is composed of pedicles (projecting from the body) and laminae (uniting arch posteriorly).

3. Transverse processes (arising from arch laterally) and spinous processes (arising from arch posteriorly) provide for attachments of muscles and ligaments.

4. Spinal nerves exit the vertebral canal via intervertebral foramina (between vertebrae) that are bordered by superior and inferior vertebral notches. (Atlas Fig. 4.4; Dissector Fig. 4.5)

5. Superior and inferior articular processes provide for articulations between adjacent vertebrae. Orientations of articular processes determine the types of movements of spinal column that can occur (orientation differs at different spinal levels).

6. Bodies of adjacent vertebrae are also joined by intervertebral discs.

B. Regional Variations (Snell Fig. 12-2, 12‑3) - vertebral column is divided anatomically into regions:

Cervical - 7 vertebrae numbered C1-C7 (cervical means neck)

Thoracic - 12 vertebrae numbered T1-T12 (thorax means chest)

Lumbar - 5 vertebrae numbered L1-L5 (lumbar means lower back)

Sacral - 5 fused vertebrae (individual parts still numbered S1-S5) (sacrum

means pelvis)

Coccyx - 3-5 fused vertebrae (parts Co1-Co3) (coccyx means tail)

1. Cervical vertebrae (7) ‑ typically have small bodies; transverse processes have openings called foramina transversaria for vertebral arteries and veins (small in C7); spinous processes are bifid (divided into two parts at their distal ends) for ligamentum nuchae (see below); articular processes are oriented at an angle (tilted superiorly and medially). (Atlas Fig. 4.10). Specialized cervical vertebrae are:

a. First Cervical Vertebra (C1=Atlas) ‑ has no body; is only a ring of bone with anterior and posterior arches and a lateral mass (bumps on arches at midline called anterior and posterior tubercles); articular facets on upper surface articulate with occipital bone of skull; joint permits only flexion‑extension movements (as in nodding head when saying 'yes'). (Atlas Figs. 4.10, 4.11A)

b. Second Cervical Vertebra (C2=Axis) ‑ has peg‑like odontoid process (= dens) superior to its body (may represent fused body of atlas); articulates with atlas above (atlanto‑axial joint [C1-C2] is a pivot joint allowing only for rotational movements, shaking head when saying 'no'). (Atlas Figs. 4.11B-D)

c. Seventh Cervical Vertebra (C7=Vertebra prominens) ‑ has long spinous process which is not bifid (spinous process can be palpated externally and is used to identify vertebral levels) (Atlas Figs. 4.9, 4.10); foramina transversaria are small and only transmit vertebral veins (vertebral artery only passes through cervical vertebrae 1‑6).

2. Thoracic vertebrae (12) ‑ bodies increase in size in rostral‑caudal sequence; body is heart shaped; have costal facets on bodies and transverse processes for attachments of heads and tubercles of ribs; spinous processes are long and inclined posteriorly and inferiorly; articular processes are in a coronal plane. (Atlas Fig. 4.12)

3. Lumbar vertebrae (5) ‑ large bodies, pedicles, laminae and transverse processes; articular facets are oriented in a sagittal plane. (Atlas Fig. 4.13)

4. Sacral vertebrae (5) ‑ vertebrae are fused; lateral mass represents fused transverse processes; medial crest = fused spinous processes; anterior and posterior sacral foramina = intervertebral foramina for sacral spinal nerves; sacro‑iliac joint transmits weight from vertebrae to pelvis. (Atlas Fig. 4.17)

5. Coccygeal vertebrae (3‑5) ‑ fused; rudimentary equivalent of tail bones.

C. Ligaments ‑ vertebrae held tightly together by ligaments. (Snell Fig. 12‑5; Atlas Figs. 4.24, 4.25)

1. Anterior longitudinal ligament ‑ strong band which joins bodies of vertebrae on anterior side.

2. Posterior longitudinal ligament ‑ weaker and narrower band joining bodies of vertebrae on posterior side of bodies (inside vertebral canal).

3. Ligamenta flava ‑ yellow elastic bands which connect laminae of adjacent vertebrae.

4. Interspinous and Supraspinous ligaments ‑ connect spines of vertebrae; greatly thickened in cervical region to form Ligamentum nuchae (extends from external occipital protuberance of skull to spine of the seventh cervical vertebra; supports head and neck and provides for muscle attachments). (Atlas Fig. 4.25)

D. Joints

1. Joints between articular processes are synovial plane joints which permit sliding movements. (Atlas Fig. 4.23)

2. Intervertebral discs ‑ interposed between bodies of adjacent vertebrae; each disc consists of an inner gelatinous part (nucleus pulposus) surround by collagenous fibers and fibrocartilage (anulus fibrosus). (Atlas Fig. 4.23)

Note: Herniation of Nucleus pulposus = ‘Slipped Disc’ - In the young the intervertebral discs are quite strong. Traumatic injury to the column usually results in vertebral fractures rather than damage to discs. In older people, degenerative changes can occur resulting in weakening of the anulus fibrosus. Strains applied to the back can result in disc displacement in which the nucleus pulposus bulges out, usually in a posterolateral direction (lateral to the posterior longitudinal ligament) typically at levels L4-L5 or L5-S1. This is commonly referred to as a 'slipped disc' and can produce extremely painful nerve compression.

E. Movements

1. General classes of movements

a. Flexion ‑ bending anteriorly

b. Extension ‑ bending posteriorly

c. Lateral flexion ‑ bending laterally (Snell Fig. 1‑3)

d. Rotation ‑ rotatory movements about the long axis of the spinal column.

2. Movements in Different Regions ‑ determined by the orientations of the articular facets (Atlas Fig. 4.6).

a. Cervical ‑ articular facets angled; permits considerable flexion‑extension, lateral flexion and rotation.

b. Thoracic ‑ relatively fixed; articular facets oriented in a coronal plane; permits some rotation, no flexion‑extension.

c. Lumbar ‑ articular facets oriented in a sagittal plane; permits flexion‑extension, no rotation.

F. Spinal Curvatures (Snell Fig. 12‑2A; Atlas Fig. 4.2)

1. Primary curvature ‑ whole spine is concave anteriorly at birth, remains so in adult thorax, sacrum.

2. Secondary curvatures ‑ develop in early childhood.

a. Cervical curvature ‑ concave posteriorly, develops in infants to help support head.

b. Lumbar curvature ‑ concave posteriorly, develops with walking to help support trunk.

c. Lateral curvature ‑ concave to left in right‑ handed people, concave to right in left‑handed people.

3. Abnormal curvatures

a. Kyphosis ‑ abnormal curvature that is concave anteriorly, usually found in thoracic region in elderly; 'hump' back.

b. Scoliosis ‑ abnormal lateral curvature; can be due to presence of a hemivertebra (developmental anomaly in which half a vertebra fails to develop)(Atlas Fig. 4.20D)

c. Lordosis ‑ exaggerated lumbar curvature that is concave posteriorly; often assumed by pregnant women.