8.5.8: Intervertebral Discs

Intervertebral Discs

The intervertebral discs are fibrocartilaginous pad that fills the gap between adjacent vertebral bodies. 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.

There is no intervertebral disc between the skull and atlas or between atlas and axis. There is also no intervertebral discs in between the sacral vertebrae or coccygeal vertebrae. Intervertebral discs are named according to the vertebra directly above them (i.e. the intervertebral disc between T3 and T4 vertebrae is the T3 intervertebral disc).

Above: Lateral view of the left side of the vertebral column with intervertebral discs labeled.

Each intervertebral disc consists of two parts. The anulus fibrosus is the tough, fibrous outer layer of the disc. It forms a circle (anulus = “ring” or “circle”) and is firmly anchored to the outer margins of the adjacent vertebral bodies. 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.

Above: Illustrations of intervertebral discs (right) that are normal and (left) that are herniated.

If the posterior anulus fibrosus is weakened due to injury or increasing age, the pressure exerted on the disc when bending forward and lifting a heavy object can cause the nucleus pulposus to protrude posteriorly through the anulus fibrosus, resulting in a herniated disc (“ruptured” or “slipped” disc). The posterior bulging of the nucleus pulposus can cause compression of a spinal nerve at the point where it exits through the intervertebral foramen, with resulting pain and/or muscle weakness in those body regions supplied by that nerve. The most common sites for disc herniation are the L4/L5 or L5/S1 intervertebral discs, which can cause sciatica, a widespread pain that radiates from the lower back down the thigh and into the leg. Similar injuries of the C5/C6 or C6/C7 intervertebral discs, following forcible hyperflexion of the neck from a collision accident or football injury, can produce pain in the neck, shoulder, and upper limb.

Attributions (All Vertebral Column Sections)

• "Anatomy 204L: Laboratory Manual (Second Edition)" by Ethan Snow, University of North Dakota is licensed under CC BY-NC 4.0
• "Anatomy and Physiology" by J. Gordon Betts et al., OpenStax is licensed under CC BY 4.0
• "BIOL 250 Human Anatomy Lab Manual SU 19" by Yancy Aquino, Skyline College is licensed under CC BY-NC-SA 4.0
• "BodyParts3D/Anatomography" by The Database Center for Life Science is licensed under CC BY-SA 2.1
• "Cervical vertebra english.png" by user:debivort is licensed under CC BY-SA 3.0
• "Sacrum - animation02.gif" by BodyParts3D is made by DBCLS is licensed under CC BY-SA 2.1