Anatomy 101: The Back I — Structure

Editors Note: This is a continuing series of articles on our bodies, how they function, possible problems and solutions. Go to http://www.thesouthern.com/lifestyles/mindbody to read previous articles.

While we typically think of the back as that region from the shoulders to the waist, the strict anatomical description extends from the base of the skull to the tailbone (coccyx named for its resemblance to a cuckoos beak). In effect, the back includes the entire length of the backbone (vertebral column).

The vertebral column consists of 33 individual bones (vertebrae) stacked upon one another. The bump one can feel at the lower, back part of the neck when bending the head forward is a part (the spinous process) of one of these vertebrae (the 7th cervical vertebra). The individual vertebra differ in size and shape throughout the vertebral coulumn. At the lower (lumbar) region, the vertebrae are more massive as they are required to support greater loads versus that of the upper (cervical) region.

With the exception of the lower nine vertebrae, which are fused together to form the sacrum and coccyx, these vertebrae are neither directly joined nor contiguous. Rather they are connected with one another by a series of muscles and ligaments and are separated by a series of cushions (intervertebral discs). These intervertebral discs are pliable (the inner component contains almost 90 percent gelatinous water in young people) and function as shock absorbers. The next time you see the dismount of a gymnast or acrobat you can appreciate this shock absorption function.

With age, the water content of these intervertebral discs decreases, which diminishes their shock absorption capacity and size. The reason grandma looks so much shorter now than when you were a child may not only be because of your growth but her getting shorter. As these intervertebral discs account for about 25 percent of the length of the vertebral column, the reduction in height that can occur with dehydration can be quite substantial.

The arrangement of these muscles/ligaments and intervertebral discs enables movement of the vertebral column. The greatest degree of side-to-side movement is present in the lumbar and cervical regions -- although not quite to the degree seen in The Exorcist. The ribs, which originate from the middle part of the vertebral column (thoracic vertebrae) and eventually connect with the sternum, secure this region and thereby greatly decrease the amount of movement that can occur in this mid-section. Anyone experiencing back pain almost always reports this discomfort to be located in the neck (cervical) or lower back (lumbar) and rarely in the middle (thoracic) regions. The greater extent of movement within the cervical and lumbar areas makes these sites more vulnerable to excesses in movement, which can result in the back/neck pain localized to these areas.

The next time you are at a beach or swimming pool try diverting your eyes away from the parts of the body normally scrutinized and look a persons back, particularly from a side view. You will be rewarded by this seemingly boring activity with the discovery that the back is not straight up-and-down. At the cervical and lumbar regions a forward curvature is present, while in the thoracic and coccyx regions a backward curvature is present. During fetal development, only a single C-shaped curvature is present in the vertebral column. After birth, as we develop and begin to hold our heads up and start walking, these other curvatures develop as an adaption to our upright posture.

DEAN E. DLUZEN is a retired professor anatomy and neurobiology and professor of pharmaceutical sciences. He recently relocated from Ohio to Murphysboro. Contact him at ded@neomed.edu

Read the original here:
Anatomy 101: The Back I -- Structure