General Features of the Vertebral Column

The vertebral (VUR-teh-brul) column physically supports the skull and trunk, allows for their movement, protects the spinal cord, and absorbs stresses produced by walking, running, and lifting. It also provides attachment for the limbs, thoracic cage, and postural muscles. Although commonly called the backbone, it does not consist of a single bone but a chain of 33 vertebrae with intervertebral discs of fibrocartilage between most of them. The adult vertebral column averages about 71 cm (28 in.) long, with the 23 intervertebral discs accounting for about one-quarter of the length.

As shown in figure 8.18, the vertebrae are divided into five groups, usually numbering 7 cervical (SUR-vih-cul) vertebrae in the neck, 12 thoracic vertebrae in the chest, 5 lumbar vertebrae in the lower back, 5 sacral vertebrae at the base of the spine, and 4 tiny coccygeal (coc-SIDJ-ee-ul) vertebrae. To help remember the numbers of cervical, thoracic, and lumbar vertebrae—7, 12, and 5— you might think of a typical work day: go to work at 7, have lunch at 12, and go home at 5.

Ventral view

Dorsal view

Ventral view

Dorsal view

T12 Thoracic Vertebrae

Thoracic vertebrae

Lumbar vertebrae

Thoracic vertebrae

Lumbar vertebrae

Coccyx

Sacrum

Coccyx

Figure 8.18 The Vertebral Column, Ventral and Dorsal Views.

Saladin: Anatomy & I 8. The Skeletal System I Text I © The McGraw-Hill

Physiology: The Unity of Companies, 2003 Form and Function, Third Edition

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Cervical curvature

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Thoracic curvature

L

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T12

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Lumbar curvature

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Pelvic curvature

Chapter 8 The Skeletal System 263

Chapter 8 The Skeletal System 263

Deviations Spinal Curvature With Age
Figure 8.20 Spinal Curvature of the Newborn Infant. At this age, the spine forms a single C-shaped curve.

Figure 8.19 Curvatures of the Adult Vertebral Column.

Variations in this arrangement occur in about 1 person in 20. For example, the last lumbar vertebra is sometimes incorporated into the sacrum, producing four lumbar and six sacral vertebrae. In other cases, the first sacral vertebra fails to fuse with the second, producing six lumbar and four sacral vertebrae. The coccyx usually has four but sometimes five vertebrae. The cervical and thoracic vertebrae are more constant in number.

Beyond the age of 3 years, the vertebral column is slightly S-shaped, with four bends called the cervical, thoracic, lumbar, and pelvic curvatures (fig. 8.19). These are not present in the newborn, whose spine exhibits one continuous C-shaped curve (fig. 8.20) as it does in monkeys, apes, and most other four-legged animals. As an infant begins to crawl and lift its head, the cervical region becomes curved toward the dorsal side, enabling an infant on its belly to look forward. As a toddler begins walking, another curve develops in the same direction in the lumbar region. The resulting S shape makes sustained bipedal walking possible (see insight 8.5, p. 286). The thoracic and pelvic curvatures are called primary curvatures because they are remnants of the original infantile curvature. The cervical and lumbar curvatures are called secondary curvatures because they develop later, in the child's first few years of crawling and walking.

Insight 8.4 Clinical Application

Abnormal Spinal Curvatures

Abnormal spinal curvatures (fig. 8.21) can result from disease, weakness, or paralysis of the trunk muscles, poor posture, or congenital defects in vertebral anatomy. The most common deformity is an abnormal lateral curvature called scoliosis. It occurs most often in the thoracic region, particularly among adolescent girls. It sometimes results from a developmental abnormality in which the body and arch fail to develop on one side of a vertebra. If the person's skeletal growth is not yet complete, scoliosis can be corrected with a back brace.

An exaggerated thoracic curvature is called kyphosis (hunchback, in lay language). It is usually a result of osteoporosis, but it also occurs in people with osteomalacia or spinal tuberculosis and in adolescent boys who engage heavily in such spine-loading sports as wrestling and weightlifting. An exaggerated lumbar curvature is called lordosis (swayback, in lay language). It may have the same causes as kyphosis, or it may result from added abdominal weight in pregnancy or obesity.

Saladin: Anatomy & I 8. The Skeletal System I Text I © The McGraw-Hill

Physiology: The Unity of Companies, 2003 Form and Function, Third Edition

264 Part Two Support and Movement

Scoliosis

Kyphosis ("hunchback")

Lordosis ("swayback")

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(b)

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Figure 8.21 Abnormal Spinal Curvatures. (a) Scoliosis, an abnormal lateral deviation. (b) Kyphosis, an exaggerated thoracic curvature. (c) Lordosis, an exaggerated lumbar curvature.

Figure 8.21 Abnormal Spinal Curvatures. (a) Scoliosis, an abnormal lateral deviation. (b) Kyphosis, an exaggerated thoracic curvature. (c) Lordosis, an exaggerated lumbar curvature.

2nd lumbar vertebra: superior view

Spinous process-

Superior articular facet

Transverse-

process

Vertebral foramen

Body

Intervertebral disc

Nucleus pulposus Annulus fibrosus

Superior articular facet

Transverse-

process

Vertebral foramen

Curvature Vertebral Column Enbrel

Lamina

Pedicle

Lamina

Pedicle

Vertebral arch

Figure 8.22 A Representative Vertebra and Intervertebral Disc, Superior Views.

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