Your spinal column is made up of 33 small bones (vertebrae) that are stacked on top of each other to create the spinal column. Between each vertebra is a soft, gel-like cushion called a disc that helps absorb pressure and keeps the bones from rubbing against each other. Each vertebra is held to the others by groups of ligaments. Ligaments connect bones to bones; tendons connect muscles to bones. There are also tendons that fasten muscles to the vertebrae. The spinal column also has real joints (just like the knee or elbow or any other joints) called facet joints. The facet joints link the vertebrae together and give them the flexibility to move against each other.
The discs provide both mobility and strength to the spine. Each has an outer covering (annulus fibosus) which is a firm fibroelastic mesh and an inner core (nucleus pulposus) which, when healthy, is like a thick gel.
The back or "posterior" part of the spine is non-weight bearing and allows movement by means of the facet joints. These look like knuckles and have a lot of nerve endings so are sensitive and, like most joints in the body, are prone to enlarge when they become worn. This enlargement can cause pressure on the nerve roots by blocking their exit canals.
There are a number of deep layer muscles which are important for day-to-day movement and spine stability. These attach not only to the spine but to the ribs and pelvis. The ileopsoas muscle which connects the lumbar spine to hip flexors is susceptible to chronic strain and a potent source of pain. The more superficial erector spinae muscles can often be felt in painful spasm in cases of acute lumbar disc prolapse.
Complementing the back muscles are the abdominal and flank muscles which provide support and are important in rotation and flexion of the spine.
It is useful to look at a spinal segment to understand and explain how the whole spine works. A spinal segment is made up of two vertebrae attached together by ligaments, with a soft disc separating them. The facet joints fit between the two vertebrae, allowing for movement, and the neural foramen between the vertebrae allow space for the nerve roots to travel freely from the spinal cord to the body.
The spinal segment allows us to focus on the repeating parts of the spinal column to better understand what can go wrong with the various parts of the spine. Sometimes problems in the spine involve only one spinal segment, while other times the problems involve multiple segments.
Each spinal segment is like a well-tuned part of a machine. All of the parts should work together to allow weight bearing, movement, and support. When all the parts are functioning properly, all spinal segments join to make up a remarkably strong structure called the spinal column. When one segment deteriorates to the point of instability, it can lead to problems at that segment causing pain and other difficulties.
