The five lumbar vertebrae are numbered L1 to L5. These vertebrae are much larger in size to absorb the stress of lifting and carrying heavy objects. Sacrum - the main function of the sacrum is to connect the spine to the hip bones iliac. There are five sacral vertebrae, which are fused together.
Together with the iliac bones, they form a ring called the pelvic girdle. Coccyx region - the four fused bones of the coccyx or tailbone provide attachment for ligaments and muscles of the pelvic floor. While vertebrae have unique regional features, every vertebra has three functional parts Fig.
Each vertebra in your spine is separated and cushioned by an intervertebral disc, which keeps the bones from rubbing together. Discs are designed like a radial car tire. The outer ring, called the annulus, has crisscrossing fibrous bands, much like a tire tread.
These bands attach between the bodies of each vertebra. Inside the disc is a gel-filled center called the nucleus, much like a tire tube Fig.
Discs function like coiled springs. The crisscrossing fibers of the annulus pull the vertebral bones together against the elastic resistance of the gel-filled nucleus. The nucleus acts like a ball bearing when you move, allowing the vertebral bodies to roll over the incompressible gel. The gel-filled nucleus contains mostly fluid. This fluid is absorbed during the night as you lie down and is pushed out during the day as you move upright.
With age, our discs increasingly lose the ability to reabsorb fluid and become brittle and flatter; this is why we get shorter as we grow older. Also diseases, such as osteoarthritis and osteoporosis, cause bone spurs osteophytes to grow.
Injury and strain can cause discs to bulge or herniate, a condition in which the nucleus is pushed out through the annulus to compress the nerve roots causing back pain. On the back of each vertebra are bony projections that form the vertebral arch. The arch is made of two supporting pedicles and two laminae Fig. The hollow spinal canal contains the spinal cord, fat, ligaments, and blood vessels.
Under each pedicle, a pair of spinal nerves exits the spinal cord and pass through the intervertebral foramen to branch out to your body. Surgeons often remove the lamina of the vertebral arch laminectomy to access the spinal cord and nerves to treat stenosis, tumors, or herniated discs.
Seven processes arise from the vertebral arch: the spinous process, two transverse processes, two superior facets, and two inferior facets. The facet joints of the spine allow back motion.
Each vertebra has four facet joints, one pair that connects to the vertebra above superior facets and one pair that connects to the vertebra below inferior facets Fig. 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 Figure 7.
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. 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 Figure 7. 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.
With increasing age, the water content of the nucleus pulposus gradually declines. This causes the disc to become thinner, decreasing total body height somewhat, and reduces the flexibility and range of motion of the disc, making bending more difficult. The gel-like nature of the nucleus pulposus also allows the intervertebral disc to change shape as one vertebra rocks side to side or forward and back in relation to its neighbors during movements of the vertebral column.
Thus, bending forward causes compression of the anterior portion of the disc but expansion of the posterior disc. Watch this second animation to see one possible treatment for a herniated disc, removing and replacing the damaged disc with an artificial one that allows for movement between the adjacent certebrae.
How could lifting a heavy object produce pain in a lower limb? Adjacent vertebrae are united by ligaments that run the length of the vertebral column along both its posterior and anterior aspects Figure 7. These serve to resist excess forward or backward bending movements of the vertebral column, respectively. The anterior longitudinal ligament runs down the anterior side of the entire vertebral column, uniting the vertebral bodies.
It serves to resist excess backward bending of the vertebral column. Protection against this movement is particularly important in the neck, where extreme posterior bending of the head and neck can stretch or tear this ligament, resulting in a painful whiplash injury. Prior to the mandatory installation of seat headrests, whiplash injuries were common for passengers involved in a rear-end automobile collision.
The supraspinous ligament is located on the posterior side of the vertebral column, where it interconnects the spinous processes of the thoracic and lumbar vertebrae. This strong ligament supports the vertebral column during forward bending motions. The nuchal ligament is attached to the cervical spinous processes and extends upward and posteriorly to attach to the midline base of the skull, out to the external occipital protuberance.
It supports the skull and prevents it from falling forward. This ligament is much larger and stronger in four-legged animals such as cows, where the large skull hangs off the front end of the vertebral column. You can easily feel this ligament by first extending your head backward and pressing down on the posterior midline of your neck. Then tilt your head forward and you will fill the nuchal ligament popping out as it tightens to limit anterior bending of the head and neck.
Additional ligaments are located inside the vertebral canal, next to the spinal cord, along the length of the vertebral column. The posterior longitudinal ligament is found anterior to the spinal cord, where it is attached to the posterior sides of the vertebral bodies.
Always follow your healthcare professional's instructions. Not what you're looking for? Want More Information? Cedars-Sinai has a range of comprehensive treatment options. See Our Spine Program. Choose a doctor and schedule an appointment. Find a Doctor. 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.
Vertebrae : Oblique view of cervical vertebrae. Vertebral Curvature When viewed laterally, the vertebral column presents several curves corresponding to the different regions of the column: cervical, thoracic, lumbar, and pelvic.
Cervical and Thoracic Curves The cervical curve convexes forward and begins at the apex of the odontoid tooth-like process.
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