The spine is a wonderful thing. Its flexible, yet strong, made of all of the possible types of connective tissue – bone, ligaments, cartilage, fibre and closely associated with enough muscle and tendon to consider the muscles an integral component of the spine.
It connects the head to the hips, supports the rib cage and all things heart and lung, gives a neck and a back to remind us we aren’t getting any younger and transmits stress both from above and below.
Humans are likely the only erect bipedal animals. At least most of the time. Our spines have evolved to hold our heads upright and bodies as well to make us the most efficient species on the planet. That was till cell phones and desk jobs became a thing. But our evolutionary need to stand tall and be able to look straight has caused our spines to be the sinuous curvy things that they are. When looked at from the side, fondly called the sagittal plane, the adult, erect spine shows 2 genre ’S’ curves. The thoracic spine (chest) and sacrum (the large bone right at the bottom of the spine, above the tailbone) curve outwards or backwards. That’s how we’re born. As we grow, and learn to raise our heads up the neck curves up in the opposite direction to the chest. As we learn to stand and walk the lower back curves opposite to the sacral and thoracic curves. The greeks called the outward curves, kyphosis and the inward ones lordosis. And like many things greek, like pi, and omicron, those names have stuck.
These curves are hugely important for maintaining normal movement and biomechanics. The curves ensure that the head stays above the pelvis but the weight of the head and truck does not transmit directly downwards. If it did then the disc at L4-5 which is already quite an unhappy one, would have to bear tremendous strain and fail far earlier than it does already. The curve ensures that the weight transmission is balanced out and the vector of force is not entirely downward. If it were a straight column then the entire vector of the weight would fall directly on the lowest part of the spine, causing it to degenerate and fail.
And there’s the fact that it’s the spinal curvature that helps maintain the centre of gravity when we stand. That way we don’t keel over, fall back, or strain our muscles just maintaining that standing position.
I often look at the spine as a bow. Or 3 bows one on top of the other. And the muscles of the spine as the bowstring. It’s then a bit of a chicken and egg situation to start to understand degeneration of the spine. Whether is weakening of the musculature due to poor posture that causes the spine to straighten, or degeneration of the discs and joints of the spine that that cause straightening and subsequent weakness is hard to exactly pinpoint.
What we do know is strengthening the spine helps retard degeneration, and can help is restoring normal spine curves and ease pain.
Apart from the big picture, the spine in itself is made of the vertebrae, the bones of the spine. Humans have 34. 7 in the neck. Fun fact, giraffe’s also have only 7 neck vertebrae. 12 in the thorax or chest segment, and 5 in the lumbar or low back. 5 each in the sacrum (which are usually fused), and the coccyx (which are pointless except for being, very literally, a pain in the a$$).
The first 2 bones, Atlas (since it carries the weight of the head) and axis, since during world war 2… no since that’s the bone around which the head turns, are special and merit a post of their own. The rest of the cervical, thoracic and lumbar vertebrae are largely similar in structure, barring specific differences for function.
The vertebra has a body in front, two stout pedicles that connect the body to the structures at the back which are the lamina and the spinous process. The spinous process is the bony prominence that you can feel on the back of your neck, and all along the spine in the midline.
Enclosed within this cage of the bone is the spinal canal, where the spinal cord runs.
Between two vertebrae in the front is the disc. Which absorbs shock, allows the bones to glide over each other to a small extent and is another source of constant reminders that we are aging.
And at the back the bones link with each other via facet joints.
A series of ligaments hold the spine together. Some run all along the spine and some shorter ligaments link each vertebra to the next.
And if this wasn’t enough there’s a whole set of muscles divided into intrinsic and extrinsic groups that are the tension wires to this scaffolding.
There is only one real reason the spine is important to neurosurgeons.
I mean there are others. Weakness, myelopathy, spinal cord injury, tumors, etc.
But at the root (heh!) of it all it’s pain. Stay tuned for more…