The bulging disc or nucleus material may compress the nerves or spinal cord, causing pain. Injury or aging of the annulus fibrosus may allow the nucleus pulposus to be squeezed through the annulus fibers either partially, causing the disc to bulge, or completely, allowing the disc material to escape the disc. The water content of the nucleus is about 90 percent at birth and decreases to about 70 percent by the fifth decade. The nucleus is composed primarily of loose collagen fibers, water, and proteins. This ball-like gel is contained within the lamellae. It makes up about 40 percent of the disc. The nucleus pulposus is the inner gel material surrounded by the annulus fibrosus. This creates a structure that is exceptionally strong, yet extremely flexible. The fibers of the lamellae slant at 30-degree angles, and the fibers of each lamella run in a direction opposite the adjacent layers. It is composed of layers of collagen and proteins, called lamellae. The annulus fibrosus is the outer portion of the disc. The intervertebral disc is made up of two components: the annulus fibrosus and the nucleus pulposus. Movement at a single disc level is limited, but all of the vertebrae and discs combined allow for a significant range of motion. The discs act as shock absorbers to the loads placed on the spine and allow movement of the spine. Combined, they make up one fourth the height of the spinal column. Intervertebral discs are located between each vertebra from C2-C3 to L5-S1. The spinous process is the bony projection that can be felt through the back of someone’s skin. The transverse processes extend out on either side of the laminae. The articular processes join one vertebra to another posteriorly. Ligaments and tendons attach to the processes. The articular, transverse, and spinous processes project off the laminae. This thickening compresses the spinal cord and/or nerves causing pain or numbness. Over time, the laminae may thicken, a process called stenosis. Laminae are two flattened plates of bone that form the walls of the posterior arch. If the spine becomes unstable, the pedicles may compress the nerve root, causing pain or numbness. Nerve roots branch off the spinal cord and exit to the body between the pedicles of two vertebrae. The pedicles are two short cylinders of bone that extend from the vertebral body. The posterior arch consists of the pedicles, laminae, and processes. Together, the vertebral bodies and discs bear about 80 percent of the load to the spine. Discs connect one vertebral body to another to allow motion of the spine and cushion it against heavy loads. The anterior arch is called the vertebral body. The spinal cord passes through the foramen of each vertebra. Only the first and second cervical vertebrae are structurally different in order to support the skull.Įach vertebra has an anterior arch and a posterior arch, which form a hole, called a foramen. These curves help the spine to support the load of the head and upper body and maintain balance in the upright position.Īlthough the vertebrae have slightly different appearances as they range from the cervical spine to the lumbar spine, they all have the same basic structures, and the structures have the same names. The thoracic spine has a kyphosis it curves towards the back.The neck has a lordosis, it curves towards the front.When viewed from the side, the normal spine has three gradual curves When viewed from the front or back, the normal spine is in a straight line, with each vertebra sitting directly on top of the other. The sacrum and coccyx (tailbone) are made up of 9 vertebrae that are fused together to form a solid bone.The lower back, or lumbar spine has 5 vertebrae, labeled L1-L5.The upper back, or thoracic spine, has 12 vertebrae, labeled T1-T12.The top 7 vertebrae that form the neck are called the cervical spine and are labeled C1-C7.Anatomically, the spine is divided into four regions: There are 33 vertebrae (bones) in the spine.
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