Your Healthy Spine
These days, many patients and their families want to be able to understand the medical disorder that they are encountering. To understand a spinal condition it is helpful to first understand some basics about the spine. For example: What does it do? What is it made of? What are its different parts? So, this section will present you with an overview of a healthy spine.
The spine has three major components:
- the spinal column (i.e., bones and discs)
- neural elements (i.e., the spinal cord and nerve roots)
- supporting structures (e.g., muscles and ligaments)
The Spinal Column (fig. 1)
The spinal column consists of individual bones called vertebrae, (fig. 2) the building blocks, which provide support for the spine. These vertebrae are connected in the front of the spine by intervertebral discs. (fig. 2) Discs are very strong tissues, which are filled with a gel. Discs help to support the spine, and also allow it to move. Many ligaments and muscles (fig. 3.) attached to the back of the spine (posterior aspect) provide power for movement.
Vertebrae in the Spinal Column
You may have heard your doctor using such terms as lumbar spine, or L5. These terms are easy and important to understand. The spinal column (fig. 1) consists of:
- seven cervical vertebrae (C1–C7) i.e. neck
- twelve thoracic vertebrae (T1–T12) i.e. upper back
- five lumbar vertebrae (L1–L5) i.e. lower back
- five bones (that are joined, or "fused," together in adults) to form the bony sacrum
- and three to five bones fused together to form the coccyx or tailbone.
Each vertebrae is numbered from the top of the spine to the bottom, so the top vertebra in the lumbar spine is called L1, while the bottom vertebra in the lumbar spine is called L5.
In general a typical vertebra consists of a:
- large vertebral body in the front
- two strong bony areas called pedicles connecting the vertebral body and the posterior arch
- an arch of bony structures in the back (posterior arch)
The exterior vertebral body consists of very hard bone (cortical bone), with more spongy bone (cancellous bone) and blood vessels inside. The vertebral bodies support 80% of all of the loads applied to the spine. (For example, if you pick up a heavy object, that load is primarily supported in the spine by the vertebral bodies.)
The posterior arch consists of several bony structures (e.g., the spinous process, the transverse process, etc). The main purpose of these structures is to protect the spinal cord, and to enable the connection of the vertebrae of muscles and ligaments.
How the Spinal Column Should Look
When looking at the spinal column from the back (posterior aspect), it should be perfectly straight, with no sideways (lateral) curves. (see fig. 4)
When looking at the spinal column from the side (sagittal view), there should be inward curves (lordosis) at the cervical and lumbar levels, and an outward curve (kyphosis) at the thoracic level. These curves allow the head to position over the pelvis in a sitting and standing position, while allowing for load bearing and shock absorption in the spine.(see fig. 4)
The neural elements consist of the spinal cord and nerve roots.(see fig. 5)
The spinal cord runs from the base of the brain down through the cervical and thoracic spine (i.e., about two thirds of the way down your back). Below the L1–L2 level the spinal cord ends, as an array of nerve roots continues, looking somewhat like a horse's tail (cauda equina). (see fig. 6)
The spinal cord is surrounded by spinal fluid (CSF) and by several layers of protective structures, including the dura mater, the strongest, outermost layer.
At each vertebral level of the spine there are a pair of nerve roots. These nerves go to supply particular parts of the body.
The muscles and ligaments (soft tissue supporting structures of the spine) (see fig.3) enable the spine to function in an upright position, and the trunk to assume a variety of positions for various activities.
The spinal ligaments are extremely important for connecting the vertebrae and for keeping the spine stable. There are various ligaments attached to the spine, with the most important being the anterior longitudinal ligament (see fig.7) and the posterior longitudinal ligament (see fig.7), which runs from the skull all the way down to the base of the spine (the sacrum).
In addition to the ligaments, there are also many muscles attached to the spine, which further help to keep it stable. The majority of the muscles are attached to the posterior (back) elements of the spine.