The Spine

The spine is the core of our body and in yoga we often refer to ‘our centre’

Anatomy

The spine is made up of stacks of short round bones (vertebrae) with fluid like discs of cartilage between them.
The intervertebral discs provide shock absorption and allow movement by maintaining space between the bones.
Nerves flow down the spinal cord and feed to other tissues and organs.
Various structures attach to the spine (directly and indirectly) including the ribs, lungs, heart, organs, diaphragm, pelvic floor muscles, psoas and other myofascia.

Movement

The joints in the spine allow movement in all directions but there is only a small range of movement.

The joints move relative to one another.

Tension on the spine

Imbalance of tension adds stress and strain on the spine, especially over time.

Shape of the Spine

There are natural curves running through the spine. These add strength to the structure.

Bones of the Spine

Spinous Process – the part of the vertebra that sticks out posteriorly. The muscles attach here.
Transverse Process – The part of the vertebra that sticks out to either side.
Body of the Vertebra – this is the part of the vertebra that sandwiches the disc along the front of the spine. The vertebra stack on top of each other. The body of each vertebra is designed to support weight.
Vertebral Foramen – The vertebra create a ring of bone (the vertebral foramen) which encases the spinal cord.

Lumbar Spine

Vertebra is larger at the bottom of the spine in order to support the structure above.
The shape of the vertebrae also changes up the spine to restrict movement in certain places.
The joints move relative to one another and it also allows for side bending (flexion).
There is a deep curve in the lumbar spine that is filled with thick muscles.

Thoracic Spine

This area is twice as long as the lumbar area.
Vertebrae are smaller as there is less weight bearing required compared to the lumbar.
One rib is attached to the vertebra on either side. This restricts movement. There are 10 pairs of ribs. The facet joints do not slide easily past each other like in the lumbar spine so this also restricts movement.
Greater movement is allowed through movement across all the vertebrae and individual vertebra has limited movement.

Cervical Spine

Lacks the outer support of the ribs.
There is more space between the vertebrae allowing for extension in this area of the spine.
The cervical vertebrae rely on the base of the solid thoracic vertebrae so that they can focus on supporting the head.
There is a lot of flexion and extension in this area of the spine.
Atlas – this is the top vertebrae (C1) of the spine that meets the occiput bone to support the skull. This atlanto-occipital joint allows the skull to tilt. Rotation at this joint is limited.
Axis – the second to top vertebrae of the spine (C2). There is some projection here to provide the skull with a greater range of rotation.

Muscles of the Spine

Posterior Spinal muscles – the muscles in the back maintain the spine in an upright position. These muscles will work in backbends and in poses like locust.

Abdominals (oblique, transverse abdominals, rectus abdominis) – stabilize and move the spine.

The obliques work in lateral flexion or side bending. They can also restrict movement.

The abdominals can also move/stabilise the pelvis (e.g. plank, boat pose).

These muscles also act as secondary muscles in respiration. They push on the diaphragm and compress the lungs to push out air.

Ligaments of the Spine

The ligaments stabilize, support and allow for or restrict movement.
The main ligaments of the spine run through the entire length.
Anterior (front) Longitudinal (lengthwise) ligament (ALL) – thick and dense ligament that attaches to the front of the vertebrae where the fibres of the ligament weave themselves into the fabric of the connective tissue of the bone (vertebrae) and the disc. It runs from the sacrum to the skull.
Posterior (back) longitudinal ligament (PLL) – runs up the entire length of the back of the spine and connects to the vertebrae and discs. The ALL and PLL sandwich the discs and add extra resistance to prevent herniations.
Ligamentum Flavum – functions with the ALL
Supraspinous ligament – attaches the spinous processes with a thick cord of connective tissue. Resists spinal flexion.
Interspinous ligament – runs between the spinous processes. Resists spinal flexion.

Discs

Nucleus Pulposus – fluid is forced against the cartilaginous ring. The more fluid contained in the disc, the more pressure. The fluid is re-absorbed into the disc at night but gets absorbed into the surrounding bones during the day.
Annulus Fibrosis (cartilaginous ring) – The cartilage surrounds the fluid on the sides but not above or below the nucleus (only bone).