Anatomy of the Spine

The human spine is a complex set of bones, ligaments, tendons, and nerves that provide a lifeline to many parts of the human body.  No short article can explain, in detail, the parts of the spine.  This one, however, will provide a basic understanding of the most important parts of the spine and give you a starting place for further research. 

The Spinal or Vertebral Column

When we think of “the spine” the vertebral column may be one of the first things that comes to mind.  The spinal column is made up of 33 vertebrae.  These small bones are stacked one on top of the other and connect the skull to the pelvis.  Each vertebrae has a hole in the center of the bone structure; when the vertebrae are stacked in the spinal column, these holes form the spinal canal.  The vertebrae are divided into four working groups: cervical, thoracic, lumbar, and sacrum.  The final four vertebrae after the sacrum are fused together and have no medical function.  They make up the coccyx or tailbone.       

Intervertebral Discs

Intervertebral discs are located between the vertebrae.  They are made up of cartilage with a jelly-like center, the nucleus pulposus, surrounded by a more fibrous, supportive covering, the annulus fibrosus.  The discs hold the vertebrae together, allow for flexibility in the spine, and absorb any shock to the spine, protecting the spinal cord and other nerves from damage.  Discs can degenerate and cause severe pain, both because there is instability between the vertebrae and because protein from the nucleus pulposus leaks out of the disc and inflames the nearby nerves.

Spinal Cord and Spinal Nerves

The spinal cord runs from the base of the skull through the cervical and thoracic vertebrae (the first 19 vertebrae) through the spinal canal. At the lower end of the thoracic group, the spinal cord branches into different spinal nerves.  These nerves travel through the lumbar, sacrum, and coccyx vertebrae.  There are five lumbar nerves, five sacrum nerves, and one coccygeal nerve.  At the lower end of each group of vertebrae, the spinal nerves pass through a space between two vertebrae and leave the spinal column.  Sometimes, these nerves are pinched as they leave the spinal column, causing pain in the legs and/or arms, depending on the nerve pinched.    

The Back Muscles

Three types of muscles make up the back: extensors, flexors, and obliques.  Each group of muscles performs a specific function in our everyday activities. 

Extensor muscles help us stand, sit up, and lift objects.   They, in other words, “extend” the back and help make it straight.  The erector spinae (two lower back muscles attached to the back side of the spine) and the gluteal muscles comprise the extensor group. 

Flexors help us to bend forward and “flex” the spine.  They are located on the front side of the spine. Abdominal muscles are also part of the flexor group. 

Obliques help us to twist our upper bodies.  They are located on the sides of our spine.  They, along with extensors and flexors, help to stabilize the spine and protect it from injury. 

Facet Joints

The joints in the spinal or vertebral column are called facet joints.  Facet joints connect the vertebrae to one another with cartilage. The joints help to stabilize each vertebrae and the spine when we twist our necks or lower backs. 

Ligaments and Tendons 

The ligaments in the back work similarly to those in other parts of the body.  Ligaments have one primary function: to hold bones together.  There are two types of ligaments in the spine, intrasegmental and intersegmental.  The intrasegmental ligaments connect individual vertebrae and the intersegmental ligaments connect many different vertebrae. Neither as pliable as muscle nor as hard as bone, ligaments support the spine.  When we are standing up, the ligaments are at their normal length; when we are bent over, they are stretched to their maximum length.  Poor posture can affect the ligaments’ strength, causing them to stretch in unusual and unhealthy ways.   

While ligaments hold bones together, tendons connect muscles to bones.  Like ligaments, tendons are less elastic, collagen-based tissues.  Tendons in the back connect the back muscles to the vertebrae that make up the spinal column.  The tendons and ligaments work in conjunction with one another to provide a support system for bones and muscles.

Both ligaments and tendons can tear away from the bones, either from sudden injury or from general aging, causing back pain.  After an injury, they can take longer to heal because very little blood circulates within them.      

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