Spine

Vertebrae & Discs

The spine is quite literally the core of our body & a key anatomical component for accessing & understanding our nervous system as the spinal column contains the all important spinal cord. The spine is comprised of 33 bones that are designed to support weight as they stack atop one another. Between each vertebrae, there are fluid-filled cartilage discs that absorb shock & create space for the nerves coming off of the spinal cord to feed their tissues. If there isn’t enough space, the bones or discs may press on the nerve roots, often resulting in a painful sensation down that nerve line. Balance among the surrounding muscles of the spine is key to prevent or minimize long-term disc injuries such as bulging discs, ruptured discs, & herniated discs, though disc injuries can also stem from genetic code, age, & disc degeneration.

The space as created by the discs also allows for movement of the spine. The flat surfaces along the tops & bottom of each vertebra are called facet joints. These vary in size & orientation & allow for or restrict movement depending on where they are located along the spine. 

Each round vertebrae has a spinous process that shoots off backward & two transverse processes that shoot off to either side. These bones also allow for & restrict movement depending on their size, orientation, & location along the spine. Additionally, the spinous & transverse processes provide attachments for deep muscle & fascia & create incredible strength along the spine. Together, the body of the vertebrae, the spinous process, & two transverse process on either side create a continuous ring known as the vertebral foramen. Within the vertebral foramen is the spinal cord.

Movements by Region of the Spine

The movements of the spine depend on the region & movement we are targeting.

• The sacrum is usually a fusion of 5 vertebrae & the coccyx, or tailbone, is usually a fusion of 4 vertebrae, though it is possible to have an extra vertebrae in either the sacrum or tailbone regions. As this region supports the entire spine above it, the vertebrae here are much larger.
• There are 5 vertebrae in the lumbar spine of the low back. The lumbar area allows for flexion, lateral flexion (or sidebending), & extension, but the way the vertebrae are aligned atop one another prevents them from doing too much rotation. 
• The thoracic vertebrae is built for lots of movement, & more specifically, rotation. There are 12 vertebrae in the thoracic spine of the upper & middle back. The thoracic vertebrae have a slightly different size, shape, & orientation of alignment that allows them to function differently than the lumbar vertebrae. As they do not support as much weight as the lumbar vertebrae, their size is much smaller. In terms of movement, flexion & extension of the spine are fairly restricted in this area. The primary function of the thoracic region is rotational movement. Lateral flexion is also available & will only be restricted by the ribs bumping into one another & the tightness of the intercostal muscles, located between the ribs, on the side opposite to which you are flexing.
• There are 7 individual vertebrae in the cervical spine of the neck that primarily serve to support the head. The transverse processes become narrower & contain arteries that supply blood to the brain. The spinous process are considerably shorter, allowing for more space between the vertebrae. This creates a wonderful environment for spinal extension, though there is not much resistance for flexion, lateral flexion, or rotation, at the neck either. The one exception to that is at C1, also called atlas. This vertebrae has a wider base to hold the skull as it meets the occiput bone, referred to as the atlanto-occipital joint. This joint allows the skull to tilt forward, backward, and from side-to-side, but rotation at this joint is limited. Just below C1 is C2, also called axis. The odontoid process is a little projection that sticks up in the middle of C1, atlas. The odontoid process is what allows the skull to rotate at the atlanto-axial joint.

Rotatores

The spinal muscles share one communal goal – to stabilize & keep the spine upright. The smallest & deepest of these are the rotatores muscles. They attach to the spine directly & help to support the skeletal structure of the spinal column.

Quadratus Lumborum (QL)

The quadratus lumborum (QL) primarily functions as a stabilizer of the spine, though it does assist in spinal flexion & extension. Its attachments run from the top of the pelvis to the lowest rib & transverse processes in the lumbar spine.

Multifidus & Semispinalis

The multifidi are quite thick in the lumbar section of the spine. These actually make the lumbar curve of the spine appear much flatter than it actually is as they fill the space in the lumbar area of the back. The semispinalis attach in the thoracic & cervical areas of the spine & work to keep the spine erect.

Erector Spinae

As their name implies, these muscles help keep the spine upright & erect. The group is comprised of the spinalis, longissimus, & iliocostalis muscles, which span from the cervical vertebrae all the way to the sacrum. The most lateral muscles, the longissimus & iliocostalis attach onto the ribs & use them to help extend the spine. These muscles work in opposition to our abdominals & primarily function to extend the spine as it relates to backbends in our yoga practice.

Anterior Longitudinal Ligament (ALL)

The anterior longitudinal ligament (ALL) attaches to the front of the vertebrae & runs from the bottom of the sacrum to the base of the skull. Its thick tissue interweaves itself into the fabric of the connective tissue & bones of the spinal vertebral discs. This ligament, along with the ligamentum flavum ligament, become taught during spinal extension & prevents the spinal vertebrae from moving too far apart.

Posterior Longitudinal Ligament (PLL)

The posterior longitudinal ligament (PLL) attaches to the back of the vertebrae & also runs the length of the spine, connecting the vertebrae & the discs. It is a good bit skinnier than the ALL. It functions opposite the ALL & becomes taught during spinal flexion. The supraspinous & interspinous ligaments also resist spinal flexion. The supraspinous ligament attaches the tips of the spinous processes together while the interspinous ligament runs between the spinous processes.