Vertebral Column (Spine)
The vertebral column extends from the skull to the pelis. It consists of a series of separate bones, the vertebrae, separated by pads of fibrocartilage called the internal vertebral disks. The vertebral column is located in the middorsal region and forms the vertical axis. The skull rests on the superior end of the vertebral column, which also supports the thoracic cage and serves as a point of attachment for the pefvic girdle. The vertebral column also protects the spinal cord, which passes through a vertebral canal formed by the vertebrae. Thirty-three vertebrae are named according to their location: seven cervical (neck) vertebrae, twelve thoracic (chest) vel1ebrae, five lumbar (lower back) vertebrae, five sacral vertebrae fused to form the sacrum, and three to five coccygeal vel1ebrae fused into one coccyx.
When viewed from the side, the vertebral column has four normal curvatures named for their location. The cervical and lumbar curvatures are convex anteriorly, and the thoracic and sacral curvatures are concave anteriorly. In the fetus, the vertebral column has but one curve-concave anteriorly. The cervical curve develops three to four months after birth, when the child begins to hold the head up. The lumbar curvature develops when a child begins to stand and walk, at about one year of age. The curvatures of the vertebral column provide more support than a straight column would, and they also provide the balance needed to walk upright.
The curvatures of the vertebral column are subject to abnormalities. An abnormally exaggerated lumbar curvature is called lordosis (lor-do'sis), or "swayback." People who are balancing a heavy midsection, such as pregnant women or men with "potbellies," have swayback. An increased roundness of the thoracic curvature is kyphosis (ki-fo'sis), or "hunchback." This abnormality sometimes develops in older people. An abnormal lateral (side-to· side) curvature is called scoliosis (sko"le-o'sis), or "twisted disease." Occurring most often in the thoracic region, scoliosis is usually first seen during late childhood.
Vertebrae
The vertebral arches form the walls of the vertebral foramen (pI., foramina). The foramina form a canal through which the spinal cord passes.
There is a posteriorly placed spinous process, where the two thin plates of bone called laminae meet, and two laterally placed transverse processes, where the pedicle joins the laminae. They serve for the attachment of muscles and ligaments. There are also articular processes (superior and inferior), which serve for the joining of vertebrae.
The vertebrae have regional differences. For example, as the vertebral column descends, the bodies get bigger and are better able to carry more weight. The spinous processes are short and tend to have a dip in the cervical region; the thoracic spines are long and slender and project downward; the lumbar spines are massive and square and project posteriorly. The transverse processes of thoracic vertebrae have articular facets for ribs.
Atlas and Axis The first two cervical vertebrae are not typical. The atlas supports and balances the head. It has two depressions that articulate with the occipital condyles, allowing movement of the head forward and back. The axis has an odontoid process that projects into the ring of the atlas. When the head moves from side to side, the atlas pivots around the odontoid process.
Sacrum and Coccyx The five sacral vertebrae are fused to form the sacrum. It articulates with the pelvic girdle and forms the posterior wall of the pelvic cavity. The coccyx, or tailbone, is the last part of the vertebral column. It is formed from a fusion of three to five vertebrae.
Intervertebral Disks
The fibrocartilage disks located between the vertebrae act as a cushion. They prevent the vertebrae from grinding against one another and absorb shock caused by such movements as running, jumping, and even walking. The disks also allow motion between the vertebrae so that a person can bend forward, backward, and from side to side. Unfortunately, these disks become weakened with age, and can slip or even rupture (called a herniated disk). The damaged disk pressing against the spinal cord and/or spinal nerves causes pain. The body may heal itself, or the disk can be removed surgically. If surgery is required, the vertebrae are fused together, limiting the body's flexibility.
The vertebral column contains the cervical. thoracic, lumbar, sacral, and coccygeal vertebrae, vvhich are separated by intervertebral disks, and has four curvatures.
Thoracic Cage
The thoracic cage protects the heart and lungs, plays a role in breathing, and supports the bones of the shoulders.
Ribs
There are 12 pairs of ribs. All 12 pairs connect directly the thoracic vertebrae in the back. A rib articulates with the body and transverse process of its corresponding thoracvertebra. I:ach rib curves outward and then forward and downward.
The upper seven pairs of ribs connect directly to sternum by means of costal cartilages. These are call-"true ribs." The lower five pairs of ribs do not connect directly to the sternum, and they are called "false ribs." Three pairs of false ribs attach to the sternum by means of a common cartilage. The other two pairs are "floating ribs" because they do not attach to the sternum at all.
The sternum contains three parts: the manubrium, body and xiphoid process. The ribs articulate with the manubri and body of the sternum. In addition, the manubrium articulates with the clavicles.
The Thoracic cage contains the thoracic vertebrae, ribs and sternum.
