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Learn About the Spine

Learn About the Spine

by Casey Chan, DC, QME

The spine is an often overlooked component of the body; we usually pay more attention to the body’s organs. What is most interesting about the spine is its complex structure and function.

Structure

The spine is composed of bones, ligaments, cartilage, muscles, nerves, and blood vessels.  There are 5 major sections of bones – the cervical spine, thoracic spine, lumbar spine, sacrum, and coccyx, going from head toward the feet.

Cervical Spine has 7 bones (named C1 to C7)
Thoracic Spine has 12 bones (named T1 to T12)
Lumbar Spine has 5 bones (named L1 to L5)
Sacrum is 1 bone with 5 fused segments (each segment named S1 to S5)
Coccyx is 1 bone with 3 to 5 fused segments

Generally, the cervical spine has a lordotic curve (concave, C shape),  the thoracic spine has a kyphotic curve (convex, reverse C shape), and the lumbar spine has a lordotic curve (concave, C shape).

Each bony segment of the cervical spine, thoracic spine, and lumbar spine are called vertebra. Each vertebra is unique with its own shape and size. The spine’s vertebrae go from small to large as you move down the spine. Like all bones, these bones change in shape, size, and density depending on nutrition, usage, and presence of disease.

Each vertebra has a large joint called the vertebral body joint, connecting to either the vertebra above or the vertebra below it. Between these vertebrae are intervertebral discs made of cartilage.

Each vertebra has additional joints called “zygapophyseal” or facet joints, which connect to the facet joints from the vertebra above and below. These facet joints are oriented at a certain angle according to its function.

Ligaments at each joint hold the bones of the spine together.  With enough force and amplitude of movement, these ligaments can tear and cause significant pain.

The vertebral discs aforementioned are the same discs involved when people talk about disc bulges or disc herniations. These discs provide cushion for the spine, just like the cushion in your shoes for your feet. With stress, these cushions may wear down, get weak and bulge out from in between the vertebrae.

Many small and large muscles control the movement or static position of the spine.  There are six muscle layers. Most of the muscles are located on the sides and back of the spine. They are primarily endurance-type of muscles. Like ligaments, these muscles can tear with enough force.

The brain, located in the skull, communicates with the rest of the body through the brain stem and spinal cord. The spinal cord travels within the protected space of the spine and branches out in between each vertebrae to become nerves. These nerves serve the muscles, organs, and senses of the body. The nerves of the cervical spine generally serve the head, neck and arms. The nerves of the thoracic spine generally serve the chest wall, the mid-back, and the contents of the chest. The nerves of the lumbar spine generally serve the lower back, the genitals, the urinary bladder, the bowel, and the legs.  Injuries to the spinal cord at a certain level can affect everything at that level and below.   So, for example, neck injuries can cause paralysis from the neck all the way down to the feet.

The spinal nerves also serve the spine for pain sensation. Irritation or injury to these nerves can cause symptoms including pain, numbness, tingling, muscle weakness, and altered function in the location of injury or at distant areas.

The spine is also structurally connected to the circulatory system of the body. Blood vessels serve the bones and the nerves of the spine.  The spine also protects arteries that serve the brain.  The vertebral artery is a branch of the subclavian artery (from below the neck), and it travels up through the 6th through 1st cervical vertebrae and into the head.  Injuries to this vertebral artery can be serious due to the fact that it supplies much of the blood to the brain.

Function
There are three main functions of the spine: protection, structure, and movement.

The spine protects the spinal cord, nerves, and blood vessels. With the ribs, it also protects the body’s main organs – the heart, lungs, liver, kidneys, and spleen. Attached to the pelvic bones, it protects the intestines, urinary bladder, and reproductive organs (females) from the back.

The spine is called the backbone because it is the backbone for the rest of the bones in the body. The skull, shoulder, arms, ribs, and legs all connect to the spine. The spine provides the form of the body. Without it, we would be a lump of muscles, fat, and other tissues.

One of the most important functions of the spine is movement. The cervical spine’s primary function is for bending the head forward, backward (flexion and extension), and rotation mainly at C1 and C2. The thoracic spine’s primary function is for rotation. The lumbar spine’s primary function is bending forward, backward, and to the side at L5.

Summary

The spine plays a very important role in the body for its structure and function. It is composed of bones, ligaments, cartilage, muscles, nerves, and blood vessels. The bones, ligaments, and muscles protect the body from injury. The spine links up with the other bones of the body, and that is why it’s called the “backbone” of the body. The spine makes up the form of the body as a firm structure for tissues to connect to.  The muscles, nerves, and blood vessels radiate from the spine to help control the movement of the body.

By taking care of the spine, like other areas of the body, we are able to maintain better health and wellness for a longer, happy, productive life.

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