Stacked up like a tower of lego, the spinal column is made of 33 bones called vertebrae and is divided into five sections or regions. Our spine allows us to stand upright, bend and twist. A healthy spine has strong muscles and bones, flexible joints, ligaments and tendons, and sensitive nerves. When injury or disease affects any of these parts, we may feel discomfort or pain. The spinal column functions mainly to:
- Protect the spinal cord and related essential nerves
- Provide structural support and balance to maintain an upright posture
- Serve as an attachment for the muscles and girdles that enable movement
Have you noticed? When viewed from the side, an adult spine has three natural curves that resemble an “S” shape. The curves work like a coiled spring – absorbing shock to the spine and protecting the back from strain injuries. The main parts of the spine include:
- Intervertebral discs
- Spinal cord and nerves
- Facet joints
- Ligaments and tendons
Tip: Maintain healthy spinal curves and keep your back in shape with correct posture and regular strength exercises targeting the back and abdominal muscles.
As mentioned above, our vertebrae are numbered and divided into five regions: cervical, thoracic, lumbar, sacrum, and coccyx. Did you know? Only the top 24 bones are moveable. The vertebrae of the sacrum and coccyx are fused.
Cervical Spine (Neck)
There are seven cervical vertebrae which start with C1 and end with C7. C1, also called the “atlas”, holds the globe of the skull like the god Atlas held up the earth. C2, the “axis” permits head turning and tilting. The neck has the greatest range of motion. Because of C1 and C2, we are able to nod and pivot our heads.
Thoracic Spine (Mid Back)
The twelve thoracic vertebrae, T1 to T12, are connected to your ribs. If you follow the path of your ribs around from the front or sides of the back, you can feel where they attach to the thoracic vertebrae in the back. The main function of the thoracic spine is to hold the rib cage which protects the heart and lungs.
Lumbar Spine (Low Back)
The five lumbar vertebrae, L1 to L5, are the most massive ones. Their main function is to support the cervical and thoracic spine. The lumbar region also absorbs most of the stress of lifting and carrying objects. Therefore, many spinal problems occur in the low back because of the weight the lumbar spine has to carry.
Under the lumbar vertebrae is the sacrum – a triangular shaped bone that connects to the hips on either side. There are five sacral vertebrae, S1 to S5, which are fused together. Together with the hip bones, they form a ring called the pelvic girdle.
A small piece of bone made up of four fused vertebrae and the bottom end of the spinal column. It is named after the Greek word Kokkyx, or cuckoo because early anatomists thought it resembled a cuckoo’s beak. Its main function is to provide attachment for ligaments and muscles of the pelvic floor.
Between the vertebrae are pads called the intervertebral discs. They act as cushions and shock absorbers so your vertebrae don’t rub or bump into each other when you move. A disc is made of an outer ring called the annulus and fluid-filled centre called the nucleus.
With age, our discs increasingly lose the ability to reabsorb fluid and become brittle and flatter. This is why we get shorter as we grow older. Injuries such as back strain can cause discs to herniate. A herniated disk is a condition that can occur anywhere along the spine, but most often occurs in the low back. It is one of the most common causes of low back pain.
Spinal Cord & Nerves
The length of the spinal cord is approximately 45 cm in men and 43 cm in women. The diameter ranges from 13 mm in the cervical and lumbar regions to 6.4 mm in the thoracic area. The cord is protected within the spinal canal and runs from the brainstem to the lumbar area where the cord fibres separate. The fibres then continue down through the canal to the sacrum and coccyx where they branch off to legs.
31 pairs of spinal nerves branch off the spinal cord. The spinal nerves act as phone lines carrying messages back and forth between the body and spinal cord to control sensation and movement. The spinal cord serves as an information highway, relaying messages between the brain and the body. Damage to the spinal cord may result in a loss of sensory and motor function below the level of injury.
Back muscles stabilize the spine and support proper alignment of the vertebrae. Muscle strength and flexibility are essential to maintaining the optimal spine position (the “S” shape) and keeping the back healthy. The three types of back muscles that help the spine function are extensors, flexors and obliques:
- Extensor muscles, attached to the back of the spine, enable us to stand up and lift objects
- Flexor muscles are attached to the front and include the abdominal muscles. These muscles enable us to flex or bend forward and are important in lifting and controlling the arch in the lower back
- Oblique muscles are connected to the sides of the spine and help rotate the spine and maintain proper posture
Facet joints make the spine flexible and enable us to bend and twist. Each vertebra has four facet joints, one pair that connects to the vertebra above and one below. Nerves branch out from the spinal cord through these joints to other body parts. Healthy facet joints have cartilage, which allows vertebrae to move smoothly against each other without grinding. Each joint is lubricated with synovial fluid for additional protection against wear and tear.
Ligaments & Tendons
The system of ligaments in the spinal column (combined with the tendons and muscles) provides a natural brace to help protect the spine from injury while allowing flexion, extension, and rotation. Ligaments of the spine are strong fibrous bands that hold the vertebrae together. Tendons are similar to ligaments in characteristics, except they connect the muscles to bones.
This sums up our mini anatomy lesson, we hope you enjoyed it. If you’ve read this far down the page, you have acquired a top-level overview of the human spine. Looking to improve your back health? Feel free to consult a local chiropractor about your options.