The spinal/vertebral column extends from the skull to the pelvis and consists of individual bones known as vertebrae. It is what holds the body upright, allows the body to bend, twist, and is the conduit for major nerves running from the brain to the rest of the body. The vertebrae are grouped into four regions. They are the:
Number of Vertebrae
Area of Body
5 fused vertebrae
The cervical spine breaks down into two parts. The upper cervical C1 and C2, and the lower cervical C3 through C7. The C1 vertebrae are known as the Atlas and the C2 the Axis. The Occipital Bone is a flat bone that forms the back of the head.
The Atlas is the first cervical vertebra and is abbreviated as C1. This vertebra supports the skull. It appears different from the other spinal vertebrae, as it resembles a ring and is made up of two masses joined at the front and back by the anterior and posterior arches.
The Axis is the second cervical vertebra and is abbreviated C2. It is a tooth-like process that projects upward. It is referred to as the odontoid process or dens, which is Latin for tooth. It provides a kind of pivot and collar that allows the head along with the atlas to rotate.
The thoracic vertebrae become larger from T1 through T12. What makes the thoracic spine unique is that it is the only vertebrae that support the ribs and is made up of pedicles, spinous processes, and large neural passageways that help reduce nerve compression. Unfortunately, not everyone has a large intervertebral foramen, which can cause compression.
The thoracic vertebrae are attached to the ribs. However, at T11 and T12, the ribs are not attached and are called floating ribs. The region of the spine’s range of motion is limited because of the rib/vertebrae attachments and the long spinous processes.
The lumbar vertebrae increase in size from L1 through L5. These are the vertebrae that take the body’s weight along with any loading force that can create biomechanical stress. The pedicles are longer and wider than the thoracic spine pedicles, and the spinous processes are horizontal and more square. The neural passageway is large but nerve root compression is very common due to disc herniation from poor posture, prolonged sitting, improper lifting, etc.
The vertebrae range in size with the cervical region being the smallest. The lumbar low back region is the largest. The vertebral bodies of the spinal column are what bear the weight. The body’s upper weight is dispersed through the spine to the sacrum and pelvis. Thee natural curves in the spine provide resistance, flexibility by distributing the body’s weight, and axial loads/forces sustained when in motion. Vertebrae are made up of many elements critical to the overall function of the spine. This includes the intervertebral discs and facet joints. Functions of the spinal/vertebral column include:
Connect Upper and Lower body
The sacrum is located behind the pelvis. It consists of five bones that are abbreviated S1 through S5. They are fused together in a triangular shape. The sacrum fits between the hipbones and connects the spine to the pelvis. The last vertebra L5 moves with the sacrum. Right below are five more bones that are also fused together and they form the Coccyx or tailbone.
The intervertebral discs make up a quarter of the spinal/vertebral column’s length. There are no discs between the Atlas, Axis, and Coccyx. Discs are not connected to the body’s vascular system and so depend on the endplates to disperse essential minerals and nutrients. The cartilaginous layers keep the discs in place. They are fibrocartilaginous cushions that function as the spine/body’s shock absorbers. They protect the vertebrae, brain, nerves, etc. There is some vertebral motion that the discs allow but individual disc movement is limited. Significant motion is possible when the discs work together.
Annulus Fibrosus and Nucleus Pulposus
Intervertebral discs are made up of an annulus fibrosus and a nucleus pulposus. The annulus fibrosus is a strong radial structure made up of lamellae. Concentric sheets of collagen fibers connect to the endplates. These sheets are positioned at various angles. The annulus fibrosus encapsulates the nucleus pulposus.
Both are made up of water, collagen, and proteoglycans. However, the larger amount of water and proteoglycans are in the nucleus pulposus. Proteoglycan molecules are essential because they attract and retain water. The nucleus pulposus consists of a hydrated gel-like substance that resists compression. The amount of water in the nucleus changes throughout the day. This depends on the activity or non-activity. All in all proper care and maintenance of the spinal/vertebral column is vital to general health and overall well-being.
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