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Pointed spinous processes that slope downward; facets that articulate with ribs

Sacrum Coccyx

5 vertebrae fused into 1 bone

4 vertebrae fused into 1 bone

Dorsal sacral foramina, auricular surfaces, sacral promontory, sacral canal, sacral hiatus, pelvic sacral foramina

Attached by ligaments to the margins of the sacral hiatus

column, and Clinical Application 7.3 discusses disorders of the vertebral column.

H Describe the structure of the vertebral column.

Explain the difference between the vertebral column of an adult and that of an infant.

Describe a typical vertebra.

How do the structures of cervical, thoracic, and lumbar vertebrae differ?

Disorders of the Vertebral Column

Changes in the intervertebral disks may cause various problems. Each disk is composed of a tough, outer layer of fibro-cartilage (annulus fibrosus) and an elastic central mass (nucleus pulposus). With age, these disks degenerate—the central masses lose firmness and the outer layers thin and weaken, developing cracks. Extra pressure, as when a person falls or lifts a heavy object, can break the outer layers of the disks, squeezing out the central masses. Such a rupture may press on the spinal cord or on spinal nerves that branch from it. This condition, called a ruptured, or herniated, disk, may cause back pain and numbness or loss of muscular function in the parts innervated by the affected spinal nerves.

A surgical procedure called a laminectomy may relieve the pain of a herniated disk by removing a portion of the posterior arch of a vertebra. This reduces the pressure on the affected nerve tissues. Alternatively, a protein-digesting enzyme (chymopapain) may be injected into the injured disk to shrink it.

Sometimes problems develop in the curvatures of the vertebral column because of poor posture, injury, or disease. An exaggerated thoracic curvature causes rounded shoulders and a hunchback. This condition, called kyphosis, occasionally develops in adolescents who undertake strenuous athletic activities. Unless corrected before bone growth completes, the condition can permanently deform the vertebral column.

Sometimes the vertebral column develops an abnormal lateral curvature, so that one hip or shoulder is lower than the other. This may displace or compress the thoracic and abdominal organs. With unknown cause, this condition, called scoliosis, is most common in adolescent females. It also may accompany such diseases as poliomyelitis, rickets, or tuberculosis. An accentuated lumbar curvature is called lordosis, or swayback.

As a person ages, the intervertebral disks tend to shrink and become more rigid, and compression is more likely to fracture the vertebral bodies. Consequently, height may decrease, and the thoracic curvature of the vertebral column may be accentuated, bowing the back. ■

Thoracic Cage

The thoracic cage includes the ribs, the thoracic vertebrae, the sternum, and the costal cartilages that attach the ribs to the sternum. These bones support the shoulder girdle and upper limbs, protect the viscera in the thoracic and upper abdominal cavities, and play a role in breathing (fig. 7.40).

Ribs

The usual number of rib pairs is twelve—one pair attached to each of the twelve thoracic vertebrae. Some individuals develop extra ribs associated with their cervical or lumbar vertebrae.

The first seven rib pairs, which are called the true ribs (vertebrosternal ribs), join the sternum directly by their costal cartilages. The remaining five pairs are called false ribs because their cartilages do not reach the sternum directly. Instead, the cartilages of the upper three false ribs (vertebrochondral ribs) join the cartilages of the seventh rib, whereas the last two rib pairs have no attachments to the sternum. These last two pairs (or sometimes the last three pairs) are called floating ribs (vertebral ribs).

A typical rib (fig. 7.41) has a long, slender shaft, which curves around the chest and slopes downward. On the posterior end is an enlarged head by which the rib articulates with a facet on the body of its own vertebra and with the body of the next higher vertebra. The neck of the rib is flattened, lateral to the head, where ligaments attach. A tubercle, close to the head of the rib, articulates with the transverse process of the vertebra.

The costal cartilages are composed of hyaline cartilage. They are attached to the anterior ends of the ribs and continue in line with them toward the sternum.

Sternum

The sternum (ster'num), or breastbone, is located along the midline in the anterior portion of the thoracic cage. It

Sternal notch

True ribs

(vertebrosternal ribs)

False -ribs

Vertebrochondri ribs

Floating ribs - (vertebral ribs)

Thoracic vertebra

Clavicular notch Manubrium—i

Sternal notch

True ribs

(vertebrosternal ribs)

Vertebrochondri ribs

Floating ribs - (vertebral ribs)

Xiphoid process .

Ribs

Costal cartilage

Xiphoid process .

Ribs

Costal cartilage

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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