An interesting anatomical fact is that almost all mammals have seven cervical vertebrae, regardless of body size. This means that there are large variations in the size of cervical vertebrae, ranging from the very small cervical vertebrae of a shrew to the greatly elongated vertebrae in the neck of a giraffe. In a full-grown giraffe, each cervical vertebra is 11 inches tall.
The adult vertebral column does not form a straight line, but instead has four curvatures along its length see Figure 1. When the load on the spine is increased, by carrying a heavy backpack for example, the curvatures increase in depth become more curved to accommodate the extra weight.
They then spring back when the weight is removed. The four adult curvatures are classified as either primary or secondary curvatures. Primary curves are retained from the original fetal curvature, while secondary curvatures develop after birth.
During fetal development, the body is flexed anteriorly into the fetal position, giving the entire vertebral column a single curvature that is concave anteriorly. In the adult, this fetal curvature is retained in two regions of the vertebral column as the thoracic curve , which involves the thoracic vertebrae, and the sacrococcygeal curve , formed by the sacrum and coccyx. Each of these is thus called a primary curve because they are retained from the original fetal curvature of the vertebral column.
A secondary curve develops gradually after birth as the child learns to sit upright, stand, and walk. Secondary curves are concave posteriorly, opposite in direction to the original fetal curvature. The cervical curve of the neck region develops as the infant begins to hold their head upright when sitting. Later, as the child begins to stand and then to walk, the lumbar curve of the lower back develops.
In adults, the lumbar curve is generally deeper in females. Disorders associated with the curvature of the spine include kyphosis an excessive posterior curvature of the thoracic region , lordosis an excessive anterior curvature of the lumbar region , and scoliosis an abnormal, lateral curvature, accompanied by twisting of the vertebral column.
Developmental anomalies, pathological changes, or obesity can enhance the normal vertebral column curves, resulting in the development of abnormal or excessive curvatures Figure 2. Kyphosis, also referred to as humpback or hunchback, is an excessive posterior curvature of the thoracic region. This can develop when osteoporosis causes weakening and erosion of the anterior portions of the upper thoracic vertebrae, resulting in their gradual collapse Figure 3.
Lordosis, or swayback, is an excessive anterior curvature of the lumbar region and is most commonly associated with obesity or late pregnancy. The accumulation of body weight in the abdominal region results an anterior shift in the line of gravity that carries the weight of the body.
This causes in an anterior tilt of the pelvis and a pronounced enhancement of the lumbar curve. Figure 2. Abnormal Curvatures of the Vertebral Column. Figure 3. Osteoporosis is an age-related disorder that causes the gradual loss of bone density and strength. When the thoracic vertebrae are affected, there can be a gradual collapse of the vertebrae. This results in kyphosis, an excessive curvature of the thoracic region.
Scoliosis is an abnormal, lateral curvature, accompanied by twisting of the vertebral column. Compensatory curves may also develop in other areas of the vertebral column to help maintain the head positioned over the feet. Scoliosis is the most common vertebral abnormality among girls.
The cause is usually unknown, but it may result from weakness of the back muscles, defects such as differential growth rates in the right and left sides of the vertebral column, or differences in the length of the lower limbs.
When present, scoliosis tends to get worse during adolescent growth spurts. Although most individuals do not require treatment, a back brace may be recommended for growing children.
In extreme cases, surgery may be required. Excessive vertebral curves can be identified while an individual stands in the anatomical position. Observe the vertebral profile from the side and then from behind to check for kyphosis or lordosis.
Then have the person bend forward. If scoliosis is present, an individual will have difficulty in bending directly forward, and the right and left sides of the back will not be level with each other in the bent position. Within the different regions of the vertebral column, vertebrae vary in size and shape, but they all follow a similar structural pattern. A typical vertebra will consist of a body, a vertebral arch, and seven processes Figure 4.
The body is the anterior portion of each vertebra and is the part that supports the body weight. Because of this, the vertebral bodies progressively increase in size and thickness going down the vertebral column.
The bodies of adjacent vertebrae are separated and strongly united by an intervertebral disc. Figure 4. Parts of a Typical Vertebra. A typical vertebra consists of a body and a vertebral arch. The arch is formed by the paired pedicles and paired laminae. Arising from the vertebral arch are the transverse, spinous, superior articular, and inferior articular processes. The vertebral foramen provides for passage of the spinal cord.
Each spinal nerve exits through an intervertebral foramen, located between adjacent vertebrae. Intervertebral discs unite the bodies of adjacent vertebrae. The vertebral arch forms the posterior portion of each vertebra.
It consists of four parts, the right and left pedicles and the right and left laminae. Each pedicle forms one of the lateral sides of the vertebral arch. The pedicles are anchored to the posterior side of the vertebral body. Each lamina forms part of the posterior roof of the vertebral arch. The large opening between the vertebral arch and body is the vertebral foramen , which contains the spinal cord.
In the intact vertebral column, the vertebral foramina of all of the vertebrae align to form the vertebral spinal canal , which serves as the bony protection and passageway for the spinal cord down the back.
When the vertebrae are aligned together in the vertebral column, notches in the margins of the pedicles of adjacent vertebrae together form an intervertebral foramen , the opening through which a spinal nerve exits from the vertebral column Figure 5. Seven processes arise from the vertebral arch. Each paired transverse process projects laterally and arises from the junction point between the pedicle and lamina. The single spinous process vertebral spine projects posteriorly at the midline of the back.
The vertebral spines can easily be felt as a series of bumps just under the skin down the middle of the back. The transverse and spinous processes serve as important muscle attachment sites. A superior articular process extends or faces upward, and an inferior articular process faces or projects downward on each side of a vertebrae.
The paired superior articular processes of one vertebra join with the corresponding paired inferior articular processes from the next higher vertebra. These junctions form slightly moveable joints between the adjacent vertebrae.
The shape and orientation of the articular processes vary in different regions of the vertebral column and play a major role in determining the type and range of motion available in each region. Figure 5. Intervertebral Disc. The spine is such an important part of the human body and for this reason it must be treated with great levels of care. The anatomy of the spine is intricate, advanced, and complex; yet it cna be explained in some basic terms. The anatomy of the spine consists of the following:.
The spinal column is a bevy of different bones, ligaments, joints, tendons, muscles, and nerves. The argument is that once we reach adulthood, the two last sections fuse and become separate from the rest of the spinal column, however, for our investigation we will look at all the vertebrae as a whole. There are seven cervical vertebrae designated C1 through C7, but only the first two get a special mention.
The name references the Greek Titan that Zeus punished to stand on the edge of the world and hold up the sky on this shoulders. Therefore, the C1 vertebrae, much like the eponymous hero, supports the weight of the human head. An interesting fact is that the C2 is only found in evolved animals such as reptiles, birds, and mammals births and amphibians do not have this feature. The C3 vertebra lies snugly underneath the skin and the other spinal bones and provides a passageway to nerve endings that irrigate the face, teeth, and ears.
The following three vertebrae, C4, C5, and C6 have speech functions as they pass sound through the larynx and vocal cords which allow sound production. The C7 vertebra is distinctively long and is responsible for the articulation of our superior limbs.
The thoracic vertebrae are unique among the bones of the spine in that they are the only vertebrae that support ribs and have overlapping spinous processes. Another vital function of the thoracic vertebrae is rotating the upper body. Discomfort in any of the superior vertebrae, from T1 to T9 approximately, may cause breathing and heart problems. On the other hand, any interferences with the T9 - T12 vertebrae can cause digestive problems, allergic reactions, and pain in the lower limbs.
The five lumbar vertebrae are the largest of the vertebrae, their robust structure being necessary for supporting more weight than the other vertebrae.
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