The Lumbar Vertebrae
Explore the anatomy and function of the lumbar vertebrae with Innerbody's interactive 3D model.
The lumbar vertebrae consist of five individual cylindrical bones that form the spine in the lower back. These vertebrae carry all of the upper body's weight while providing flexibility and movement to the trunk region. They also protect the delicate spinal cord and nerves within their vertebral canal.
Found along the body's midline in the lumbar (lower back) region, the lumbar vertebrae make up the region of the spine inferior to the thoracic vertebrae in the thorax and superior to the sacrum and coccyx in the pelvis. The lumbar vertebrae are stacked to form a continuous column in order from superior (L1 or first lumbar vertebra) to inferior (L5 or fifth lumbar vertebra). Together they create the concave lumbar curvature in the lower back.
Connecting each vertebra to its neighboring vertebra is an intervertebral disk made of tough fibrocartilage with a jelly-like center. The outer layer of the intervertebral disk, the annulus fibrosus, holds the vertebrae together and provides strength and flexibility to the back during movement. The jelly-like nucleus pulposus acts as a shock absorber to resist the strain and pressure exerted on the lower back.
The lumbar vertebrae are the some of the largest and heaviest vertebrae in the spine, second in size only to the sacrum. A cylinder of bone known as the vertebral body makes up the majority of the lumbar vertebrae's mass and bears most of the body's weight. Posteriorly the body is connected to a thin ring of bone known as the arch. The arch surrounds the hollow vertebral foramen and connects the body to the bony processes on the posterior of the vertebra. The vertebral foramen is a large, triangular opening in the center of the vertebra that provides space for the spinal cord, cauda equina, and meninges as they pass through the lower back.
Extending from the vertebral arch are several bony processes that are involved in muscle attachment and movement of the lower back. The spinous process extends from the posterior end of the arch as a thin rectangle of bone. It serves as a connection point for the muscles of the back and pelvis, such as the psoas major and interspinales. On the left and right lateral sides of each vertebra are the short, triangular transverse processes. The transverse processes form important connection points for many muscles, including the rotatores and multifidus muscles that extend and rotate the trunk.
Unlike the cervical vertebrae in the neck, the lumbar vertebrae lack the transverse foramina in the transverse processes, and also lack facets to either side of the body. The fifth lumbar vertebra is distinct from the L1-4 vertebrae in being much larger on its front side than in the back. Its spinous process, on the other hand, is smaller than in the other lumbar vertebrae with a wide, four-sided shape that comes to a rough edge and a thick notch.
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