Lumbar Spine
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The spine acts as a conduit for precious neural structures and possesses the physiological capacity to act as a crane for lifting and a crankshaft for walking.
It protects the spinal cord.
The spine is composed of the vertebral bones and intervertebral disks.
There are 7 cervical (C), 12 thoracic (T), and 5 lumbar (L) vertebrae. The sacrum is a fusion of 5 sacral (S) vertebrae, and there are small rudimentary coccygeal vertebrae.
At each vertebral level, paired spinal nerves exit the central nervous system.
The lumbar vertebrae are the 5 largest and strongest of all vertebrae in the spine. The strongest stabilizing muscles of the spine attach to the lumbar vertebrae.
The spine is made up of three segments. When viewed from the side, these segments form three natural curves. The "c-shaped" curves of the neck (cervical spine) and lower back (lumbar spine) are called lordosis. The "reverse c-shaped" curve of the chest (thoracic spine) is called kyphosis.
These curves are important to balance and they help us to stand upright. If any one of the curves becomes too large or small, it becomes difficult to stand up straight and our posture appears abnormal.
Abnormal curvatures of the spine are also referred to as spinal deformity. These types of conditions include kyphosis of the thoracic spine ("hunchback") and lordosis of the lumbar spine ("swayback").
Scoliosis is another type of spinal deformity. When viewing the spine from the front or back, scoliosis is a sideways curvature that makes the spine look more like an "S" or a "C" than a straight "I."
The anterior part of the spine consists of cylindrical vertebral bodies separated by intervertebral disks and held together by the anterior and posterior longitudinal ligaments.
The intervertebral disks are composed of a central gelatinous nucleus pulposus surrounded by a tough cartilaginous ring, the annulus fibrosis. Disks allow the bony vertebrae to move easily upon each other.
Disks allow the bony vertebrae to move easily upon each other.
Vertebral anatomy. (From A Gauthier Cornuelle, DH Gronefeld: Radiographic Anatomy Positioning. New York, McGraw-Hill, 1998; with permission.)
[Desiccation of the nucleus pulposus and degeneration of the annulus fibrosus increase with age and result in loss of disk height. ]
The disks are largest in the cervical and lumbar regions where movements of the spine are greatest. The anterior spine absorbs the shock of bodily movements such as walking and running and, with the posterior spine, protects the spinal cord and nerve roots in the spinal canal.
Sagittal section through lumbar vertebrae.
The disks are largest in the cervical and lumbar regions where movements of the spine are greatest. The anterior spine absorbs the shock of bodily movements such as walking and running and, with the posterior spine, protects the spinal cord and nerve roots in the spinal canal.
Region |
Number of Spinal Nerves |
Number of Vertebrae |
---|---|---|
Cervical |
8 |
7 |
Thoracic |
12 |
12 |
Lumbar |
5 |
5 |
Sacral |
5 |
5 (fused) |
Coccygeal |
1 |
3–4 |
Each vertebra is referred to by the first letter of its region. For example, the fourth cervical vertebra is referred to as the C4 vertebra.
A. Posterior view of the vertebral column. B. A typical thoracic vertebra. C. Two articulated vertebrae showing the ligaments. D. Lateral view of two vertebrae demonstrating intervertebral discs as shock absorbers. Observe how the facet joints facilitate flexion and extension of the vertebral column.
The anterior spine consists of cylindrical vertebral bodies separated by intervertebral disks and held together by the anterior and posterior longitudinal ligaments. The intervertebral disks are composed of a central gelatinous nucleus pulposus surrounded by a tough cartilaginous ring, the annulus fibrosis. Disks are responsible for 25% of spinal column length and allow the bony vertebrae to move easily upon each other
Vertebral anatomy. (From A Gauthier Cornuelle, DH Gronefeld: Radiographic Anatomy Positioning. New York, McGraw-Hill, 1998)
Spinal column. (From A Gauthier Cornuelle, DH Gronefeld: Radiographic Anatomy Positioning. New York, McGraw-Hill, 1998)
The disks are largest in the cervical and lumbar regions where movements of the spine are greatest. The anterior spine absorbs the shock of bodily movements such as walking and running and, with the posterior spine, protects the spinal cord and nerve roots in the spinal canal.
The posterior spine consists of the vertebral arches and processes. Each arch consists of paired cylindrical pedicles anteriorly and paired lamina posteriorly. The vertebral arch also gives rise to two transverse processes laterally, one spinous process posteriorly, plus two superior and two inferior articular facets. The apposition of a superior and inferior facet constitutes a facet joint. The posterior spine provides an anchor for the attachment of muscles and ligaments. The contraction of muscles attached to the spinous and transverse processes and lamina works like a system of pulleys and levers that results in flexion, extension, and lateral bending movements of the spine.
The spine is made up of bones, called vertebrae, which are stacked on top of one another and create the natural curves of the back.
These bones connect to create a canal that protects the spinal cord.
The spine from the front.
The spine from the back.
The cervical spine is made up of seven small vertebrae that begin at the base of the skull and end at the upper chest. The thoracic spine is made up of 12 vertebrae that start from the upper chest to the middle back and connect to the rib cage. The lumbar vertebra consists of five larger vertebrae. These vertebrae are larger because they carry more of your body's weight.
Parts of the lumbar spine.
The spinal cord extends from the skull to your lower back and travels through the middle part of each stacked vertebra, called the central canal. Nerves branch out from the spinal cord through openings in the vertebrae and carry messages between the brain and muscles.
The spinal cord ends around the first and second lumbar vertebrae in the lower back and continues as nerve roots. This bundle of nerve roots is called the cauda equina. They exit the spinal canal through openings in the vertebrae (foramen), just like other nerve roots. In the pelvis, some of the nerves group into the sciatic nerve, which extends down the leg.
The cauda equina.
These provide support and stability for your spine and upper body. Strong ligaments connect your vertebrae and help keep the spinal column in position.
Intervertebral disks sit in between the vertebrae. They are flat and round, and about a half inch thick.
Intervertebral disks are made up of two components:
When you are standing or moving, weight is put onto the nucleus. In response, the nucleus expands. The annulus holds the nucleus in place. This allows movement to take place, yet maintains the strength of the spine. In effect, disks act as shock absorbers for the spine.
The intervertebral disk is a very important structure. Many nerve endings supply the annulus and, as a result, an injured annulus can cause pain.
Healthy intervertebral disk (cross-section view).
Between the back of the vertebrae are small joints that also help your spine move. These facet joints have a cartilage surface, very much like a hip or a knee joint does. The facet joints are important for allowing rotation of the spine but may develop arthritis and become a source for low back or neck pain.
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There are two types of articulations that enable the 33 vertebrae to not only provide support, protection, and absorb shock, but also to provide flexibility.
These two articulations are the intervertebral discs and the facet joints.
Damage to the anulus fibrosus may allow the softer nucleus pulposus to bulge or herniate, which may compress the segmental nerve roots. This is often referred to as a “slipped disc.” The symptoms of this condition will depend upon the level at which the rupture occurs and the structures that are affected. For example, compression of the L4 nerve may cause weakness in ankle dorsiflexion due to the L4 innervation of the anterior tibialis muscle in the leg, or lack of cutaneous sensation in the skin over the knee due to the L4 dermatome.
A disc and its associated facet joints make up an individual motion segment. In between the disc and the facet joints lies the spinal cord or nerves and to the sides are bony struts called pedicles (see image below). Sprouting off from the spinal cord and shooting out from underneath the pedicles are the nerves, which in the lumbar spine mostly form the femoral, and sciatic nerves and in the cervical spine form the brachial plexus (the nerves which travel down the arms). In the thoracic spine the nerves supply sensation to bands of skin radiating around to the front of the chest wall and abdomen, and move the intercostal muscles to that we can inflate our lungs.
The vertebral column is stabilized by ligaments that run between vertebrae.
Some of the ligaments that limit vertebral flexion (bending forward) include the following:
Which of the following paired muscles of the back is primarily responsible for extension of the vertebral column?
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