If we look at the human backbone or spine , we can see that the vertebrae rest upon one another similarly to a stack of cotton spools .
The spine is divided into regions. There are seven vertebrae in the cervical region (neck), twelve vertebrae in the thoracic region (upper back), and five vertebrae in the lumbar region (lower back) ..
Beneath the lumbar vertebrae are found the sacrum and the coccyx. It is the lower back or lumbar and sacral regions that concern us most.
Each vertebra has a solid part in front, the vertebral body, and a hole in the back .When lined up as in the spinal column, these holes form the spinal canal. This canal serves as a protected passageway for the bundle of nerves which extends from head to pelvis-the spinal .Special cartilages, called the discs, separate the vertebrae. The discs are located between the vertebral bodies just in front of the spinal cord . Each disc consists of a soft semi-fluid centre part, the nucleus, which is surrounded and held together by a cartilage ring, the annulus or annular ligament. The discs are similar to rubber washers and act as shock absorbers.
The are able to alter their shape, thus allowing movement of one vertebra on another and of the back as a whole.The vertebrae and discs are linked by a series of joints to form the lumbar spine or low back. Each joint is held together by its surrounding soft tissues-that is, a capsule reinforced by ligaments. Ligaments can be likened to the stays that hold a mast in place on a sailing ship. If a stay were to give way, the mast will likely fall when subjected to extra strains.
Muscles lie over one or more joints of the low back and may extend upward to the trunk and downward to the pelvis. At both ends each muscle changes into a tendon by which it attaches itself to different bones.
When a muscle contracts, it causes movement in one or more joints.Between each two vertebrae there is a small opening on either side through which a nerve leaves the spinal canal, the right and left spinal nerve . Amongst other tasks, the spinal nerves supply our muscles with power and our skin with sensation. In other words, it is through the nerves that we can move ourselves and feel temperature, pressure and pain. The nerves are really part of our alarm system: pain is the warning that some structure is about to be damaged or has already sustained some damage.In the lower part of the spine some of these nerves combine on each side to form the right and left sciatic nerves. The sciatic nerves service our legs, and when compressed or irritated, they may cause pain in the leg which often extends below the knee. This is then called sciatica.
Functions of the lumbar spine:
In animals that walk on all fours, the weight of their body is distributed evenly by DISC their four legs. Most of the time the spine is held in aIl more or less horizontal position and the compressive forces that exist in upright man do not occur.
In human beings, the spine is held in a more or vertical position, at least during waking and working hours. When we are upright, , lumbar spine bears the compressive weight of the body above it transmits this weight to the pelvis when sitting and to the feet when standing, walking and running. Thus the lumbar spine, providing flexible connection between the upper and lower half of the body protects the spinal cord and also has a greater function in weight bearing. In the evolution of the horizontal-spine posture of animals to the vertical-spine posture of man, the discs between the vertebrae have adapted to support heavier weights. In addition, the spinal column has developed a series of curves that ingeniously allow for better shock absorption and flexibility.