The Structure Of The Spine
The spine is made up of over 30 bones called vertebrae, which are round bony structures that form a protective ring around the spinal cord. Vertebrae refer to two or more spinal bones and vertebra is the term that is used for one spinal bone. There are three sections of the spine that promote mobility. They are referred to as the cervical, thoracic, and lumbar spine. The bony projections that can be felt when the fingers are run along the spine are called spinous processes and these structures are attached to ligaments and muscles of the spine. There are also vertebrae in the lower parts of the spine called the sacrum or sacral spine and the coccyx (tailbone), but the vertebrae in these regions are fused together and do not move as freely.
The cervical spine is made up of seven vertebrae that are located in the neck and upper back. These vertebrae provide support and mobility for the head and neck. The first vertebra is connected to the bottom of the skull and the seventh vertebra is where the thoracic spine or the middle of the back begins. The thoracic spine consists of 12 vertebrae that promote arm movement and bending motions while providing stability for the rib cage, which encases vital organs. The first vertebra in the thoracic region or the middle of the back is connected to the lowest part of the neck and the twelfth vertebra connects the bottom of the rib cage to the top of the lumbar spine (lower back).
The lumbar spine is made up of five vertebrae that extend from the lower abdomen into the pelvis. The lowest vertebra of the lumbar spine connects to a triangular bone called the sacrum, which fits directly between the two pelvic bones. Vertebrae in the lumbar spine promote bending, stooping, sitting, and lifting. This is also the region of the back that is most susceptible to injury and the development of chronic pain. If there are no physical abnormalities along the spine, it should form two forward curves at the cervical and lumbar spine and two backward curves at the thoracic and sacral spine when it is visualized from the side through an x-ray.
The sacrum or sacral spine sits below the lumbar spine and it is a flat, triangular-shaped bone that is positioned between the hips. It is made up of five vertebrae that are fused together. The coccyx, also referred to as the tailbone, is below the sacrum and it also contains three to five fused vertebrae. Because the coccyx may consist of three to five vertebrae, an individual may have anywhere from 32 to 34 total vertebrae along the spine.
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There are bony knobs located between spinal vertebrae called facet joints. These connect vertebrae together in a chain-like manner and promote movement in a variety of directions. Except for the vertebrae that are at the top and bottom of the spine, each vertebra has one facet joint that connects it to the vertebra above it and a second one that connects it to the vertebra below it. The surface of the facet joints are covered by cartilage, which is a smooth, rubbery material that allows the vertebrae to come in contact with each other without causing friction.
Ligaments, which are strong connective tissues that attach vertebrae to one another, also provide additional stability for the spine. Although the vertebrae are connected to each other, spinal discs are located between each vertebra. The discs act as shock absorbers that protect the spine from damage during heavy activities that put a lot of strain on the spine such as running, jumping, and lifting. They also protect the spine from the daily pull of gravity. There are no spinal discs in between the vertebrae that make up the sacrum or coccyx because the vertebrae in these two regions are fused together leaving no space between them for spinal discs.
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There is also a small tunnel on the right and left side of each vertebra that spinal nerves exit from, extending into specific regions of the body including the organs and limbs. The tunnel is called a neural foramen. The nerves that come out of the tunnels that are located at the sides of the cervical vertebrae go into the arms and hands. The nerves that exit the tunnels between thoracic vertebrae extend into the upper organs, and the nerves that exit the tunnels of the lumbar vertebrae go into the lower limbs and the pelvic organs.
The spinal cord itself, which is protected by the circular-shaped vertebrae, travels from the brain down through the spine column and consists of millions of nerves. In addition, spinal vertebrae are covered by a vast amount of muscles that extend throughout the entire body. Muscles in the back help coordinate movements of the neck, upper body, and abdomen while holding the spine steady during activity.
Summary of the Anatomy of the Spine
There are three mobile sections of the spine: the cervical (neck and upper back), thoracic (mid-back), and lumbar (lower back) spine. These sections consist of seven, twelve, and five spinal vertebrae, respectively. There are also five vertebrae in the sacrum, which sits in between the pelvis and hips as well as the coccyx (tailbone), which may consist of three to five vertebrae. The vertebrae that make up the sacrum and the coccyx are fused together and therefore, these two structures do not move as freely. Due to the fact that the number of vertebrae in the coccyx may vary, an individual may have between 32 and 34 vertebrae along the spine.
The vertebrae in the cervical, thoracic, and lumbar regions of the spine are connected in a chain-like manner by facet joints. Ligaments also connect vertebrae to one another in order to provide added stability. Spinal nerves exit the sides of the vertebrae through a small tunnel and spinal discs that act as shock absorbers are located between the vertebrae. Furthermore, the vertebrae form a protective ring around the spinal cord, which consists of millions of nerves that control numerous processes in the body.
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