The Structural Anatomy of the Spine
The spine - lateral view
Your spine is a masterpiece of engineering. It consists of 33 vertebrae, 5 of which are fused at the sacrum and 4 are fused at the coccyx while the remaining 24 are free to articulate with each other, the ribs, the sacrum and the skull to create a structure that elegantly combines mobility and stability.
It is supported by muscle and connective tissue. Close to the spine a layer of ligaments connect individual vertebrae and the entire spinal column at both the front and the back of the spine. Smaller muscles close to the spine connect adjacent vertebrae while the larger, more superficial ones span sections of the spine.
At adjacent vertebrae four intervertebral, or facet, joints open and close to facilitate relatively small movements, the combination of which results in the overall movement of the spine.
The spine contains and protects the spinal cord, the part of the central nervous system that links to the rest of the body. This important function defines much of it's biomechanics as the vital role of maintaining the integrity of the nervous system must take precedence over the need for mobility.
The vertebrae
The vertabrae - lateral view
Vertebrae - superior view
Vertebrae vary depending on their location but most of them share the same basic structure. Anteriorly the vertebral body is the weight bearing structure so it is larger in lumbar region and smaller higher up in the neck. Intervertebral discs lie in between these vertebral bodies to cushion the forces between them. Posteriorly the spinous process and two transverse processes provide connection sites for muscles. The empty space in the middle makes up a section of the spinal canal.
Small bony projections called facets sit above and below the vertebrae. The shape of the superior facet complements that of the inferior facet in the above vertebrae so that they fit against each other at a facet joint. Four of these joints above each vertebrae and four below open and close as individual vertebrae move. These small movements occur up and down the spine and accumulate into the larger movements of the spine itself.
These movements are of course orchestrated by the myofascia and it's master the nervous system. Small muscles connect adjacent verterbrae and control the movements at individual facets. Larger muscles that move the spine as a whole also affect these facet joints because this is the only way that the spine can move. In these movements however lots of joints open and close so there is room for compensation when some don't want to play the game.
Facets meet each other at particular angles that determine both the direction and the degree of movement that is possible at each one. Occasionally, for a variety of reasons, some of these facet joints will be locked, either open or closed, and the vertebrae won't move in a certain direction, this is often referred to as joint subluxation. If posterior facet joints are locked closed the superior vertebrae will be displaced slightly posteriorly and not able to bend forward, this is common when the upper back stiffens up to compensate for an excessive lumbar curve or sway back.
These sort of local joint dysfunctions co-exist with the myofascial imbalances associated with more general postural dysfunction. Whether the locked joint causes the stiff back or the myofascial loading overloads the joint is a matter of debate amongst folks who like to debate such things. In the real world they exist together and both need to be resolved. It is entirely possible for us to address myofascial loading with exercise, stretching and changes to technique. Depending on the degree of subluxation you'll more than likely need someone to help. If unsure ask your doctor, generally osteopaths and chiropractors treat joint dysfunction, some physical therapists are also licenced to do this but you need to check, the regulations are different across jurisdictions.