Key Points The human spine consists of 24 articulating vertebrae grouped into cervical, thoracic, and lumbar regions. Nine more vertebrae make up the sacrum and coccyx. Typical vertebrae consist of the anterior vertebral body and the posterior section, which contains the vertebral foramen through which the spinal cord passes. There are four main curves of the spine: cervical, thoracic, lumbar, and pelvic.
Facets of the vertebrae restrict range of movement to prevent shearing of the spinal cord. Blood vessels and nerves exit the spinal column at intervertebral foramina. There are four main curves of the spine: cervical, thoracic, lumbar and pelvic. Key Terms vertebrae : The bones that make up the spinal column.
Number of Vertebrae Vertebral Column : The sections of the vertebral column. Vertebral Shape A typical vertebra consists of the vertebral body and vertebral arch. Excessive kyphosis or increased angulation forward can be due to trauma or other causes. Scoliosis or a lateral curvature of the spine viewed from the back may be corrected with surgery. There are many types of kyphosis and scoliosis that only need careful observation.
Skip to content. Curves of the Spine Not what you're looking for? Start New Search. About Curves of the Spine The normal spine has an S-shaped curve when viewed from the side.
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 7. 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 7.
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 7. 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. 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. Osteoporosis is a common age-related bone disease in which bone density and strength is decreased.
Watch this video to get a better understanding of how thoracic vertebrae may become weakened and may fracture due to this disease. How may vertebral osteoporosis contribute to kyphosis? 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 7. 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.
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. 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 [link].
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.
Intervertebral Disc The bodies of adjacent vertebrae are separated and united by an intervertebral disc, which provides padding and allows for movements between adjacent vertebrae.
The disc consists of a fibrous outer layer called the anulus fibrosus and a gel-like center called the nucleus pulposus. The intervertebral foramen is the opening formed between adjacent vertebrae for the exit of a spinal nerve.
Regional Modifications of Vertebrae In addition to the general characteristics of a typical vertebra described above, vertebrae also display characteristic size and structural features that vary between the different vertebral column regions.
Thus, cervical vertebrae are smaller than lumbar vertebrae due to differences in the proportion of body weight that each supports. Thoracic vertebrae have sites for rib attachment, and the vertebrae that give rise to the sacrum and coccyx have fused together into single bones. Typical cervical vertebrae , such as C4 or C5, have several characteristic features that differentiate them from thoracic or lumbar vertebrae [link].
Cervical vertebrae have a small body, reflecting the fact that they carry the least amount of body weight. Cervical vertebrae usually have a bifid Y-shaped spinous process. The spinous processes of the C3—C6 vertebrae are short, but the spine of C7 is much longer.
You can find these vertebrae by running your finger down the midline of the posterior neck until you encounter the prominent C7 spine located at the base of the neck. The transverse processes of the cervical vertebrae are sharply curved U-shaped to allow for passage of the cervical spinal nerves. Each transverse process also has an opening called the transverse foramen.
An important artery that supplies the brain ascends up the neck by passing through these openings. The superior and inferior articular processes of the cervical vertebrae are flattened and largely face upward or downward, respectively.
The first and second cervical vertebrae are further modified, giving each a distinctive appearance. The first cervical C1 vertebra is also called the atlas , because this is the vertebra that supports the skull on top of the vertebral column in Greek mythology, Atlas was the god who supported the heavens on his shoulders. The C1 vertebra does not have a body or spinous process.
Instead, it is ring-shaped, consisting of an anterior arch and a posterior arch. The transverse processes of the atlas are longer and extend more laterally than do the transverse processes of any other cervical vertebrae. The superior articular processes face upward and are deeply curved for articulation with the occipital condyles on the base of the skull. The inferior articular processes are flat and face downward to join with the superior articular processes of the C2 vertebra.
The second cervical C2 vertebra is called the axis , because it serves as the axis for rotation when turning the head toward the right or left.
The axis resembles typical cervical vertebrae in most respects, but is easily distinguished by the dens odontoid process , a bony projection that extends upward from the vertebral body. The dens joins with the inner aspect of the anterior arch of the atlas, where it is held in place by transverse ligament.
Thoracic Vertebrae The bodies of the thoracic vertebrae are larger than those of cervical vertebrae [link]. The characteristic feature for a typical midthoracic vertebra is the spinous process, which is long and has a pronounced downward angle that causes it to overlap the next inferior vertebra.
The superior articular processes of thoracic vertebrae face anteriorly and the inferior processes face posteriorly. These orientations are important determinants for the type and range of movements available to the thoracic region of the vertebral column. Thoracic vertebrae have several additional articulation sites, each of which is called a facet , where a rib is attached.
These are for articulation with the head end of a rib. An additional facet is located on the transverse process for articulation with the tubercle of a rib. Rib Articulation in Thoracic Vertebrae Thoracic vertebrae have superior and inferior articular facets on the vertebral body for articulation with the head of a rib, and a transverse process facet for articulation with the rib tubercle. Lumbar Vertebrae Lumbar vertebrae carry the greatest amount of body weight and are thus characterized by the large size and thickness of the vertebral body [link].
They have short transverse processes and a short, blunt spinous process that projects posteriorly. The articular processes are large, with the superior process facing backward and the inferior facing forward. Sacrum and Coccyx The sacrum is a triangular-shaped bone that is thick and wide across its superior base where it is weight bearing and then tapers down to an inferior, non-weight bearing apex [link].
It is formed by the fusion of five sacral vertebrae, a process that does not begin until after the age of On the anterior surface of the older adult sacrum, the lines of vertebral fusion can be seen as four transverse ridges. Similarly, the fused transverse processes of the sacral vertebrae form the lateral sacral crest. The sacral promontory is the anterior lip of the superior base of the sacrum.
Lateral to this is the roughened auricular surface, which joins with the ilium portion of the hipbone to form the immobile sacroiliac joints of the pelvis. Passing inferiorly through the sacrum is a bony tunnel called the sacral canal , which terminates at the sacral hiatus near the inferior tip of the sacrum.
Each of these openings is called a posterior dorsal sacral foramen or anterior ventral sacral foramen. These openings allow for the anterior and posterior branches of the sacral spinal nerves to exit the sacrum. The superior articular process of the sacrum , one of which is found on either side of the superior opening of the sacral canal, articulates with the inferior articular processes from the L5 vertebra.
The coccyx, or tailbone, is derived from the fusion of four very small coccygeal vertebrae see [link]. It articulates with the inferior tip of the sacrum. It is not weight bearing in the standing position, but may receive some body weight when sitting. Intervertebral Discs and Ligaments of the Vertebral Column The bodies of adjacent vertebrae are strongly anchored to each other by an intervertebral disc. This structure provides padding between the bones during weight bearing, and because it can change shape, also allows for movement between the vertebrae.
Although the total amount of movement available between any two adjacent vertebrae is small, when these movements are summed together along the entire length of the vertebral column, large body movements can be produced. Ligaments that extend along the length of the vertebral column also contribute to its overall support and stability. An intervertebral disc is a fibrocartilaginous pad that fills the gap between adjacent vertebral bodies see [link]. Each disc is anchored to the bodies of its adjacent vertebrae, thus strongly uniting these.
The discs also provide padding between vertebrae during weight bearing. Because of this, intervertebral discs are thin in the cervical region and thickest in the lumbar region, which carries the most body weight.
In total, the intervertebral discs account for approximately 25 percent of your body height between the top of the pelvis and the base of the skull. Intervertebral discs are also flexible and can change shape to allow for movements of the vertebral column.
Each intervertebral disc consists of two parts. The anulus fibrosus is the tough, fibrous outer layer of the disc. Inside is the nucleus pulposus , consisting of a softer, more gel-like material. It has a high water content that serves to resist compression and thus is important for weight bearing.
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