Today’s post looks at your spine, with a quick introductory tour of this amazing structure. One day we’ll explore individual areas of the vertebral column in detail — today, though, we’ll start with an overview.
Your spine is the base for all your movement, the centre of everything you do, and the main wiring conduit for the control systems which power your dance. It has 32 to 35 bones — 24 of these are mobile, while the others are fused together[1].
Your vertebral column reaches from the base of your skull all the way down to your tailbone. Together with your skull and your ribs, it makes up your “axial skeleton”. (All the other bits — arms, pelvis, legs, collarbones, shoulder-blades and so on — are the “appendicular skeleton”, hanging on the central axis of your spine).
The sections of your back are classified by region. The top seven bones, supporting your neck, are the cervical vertebrae, numbered C1 to C7, starting from the top. Directly beneath C7 are the twelve vertebrae of your thorax, T1 to T12. Moving down the spinal column you have L1 to L5, the lumbar vertebrae, then S1 to S5, the fused bones of your sacrum. (This is the central rear part of your pelvis, joined at each side to the ilia which curve around forwards to form your hip bones). It all finishes at your coccyx or tailbone, three to five small bones, fused during growth. The regions of your spine are shown in Figure 1.
Fig. 1: Regions of the spine
At rest, a healthy spine curves in both anterior – forward — and posterior – backward — directions. As a foetus, you had only one curve, the so-called primary curve. During growth, secondary curves develop[2], probably due to movements like lifting the head, sitting, crawling or walking. The curves adjust and rebound under stress, like the springs of a mattress, enabling you to lift, walk, run, jump, and land, absorbing shock and protecting each vital component of your instrument.
Your spine can twist, flex and bend forwards, backwards or sideways, starting from and returning to its normal convex or concave curves. A spine which is permanently bent or twisted sideways is suffering from scoliosis, an abnormal condition needing diagnosis and perhaps treatment. This also applies where the normal forward and backward curves are exaggerated. Excessive backwards curvature in the thorax is called kyphosis (the round-shouldered stance) — exaggerated forwards lumbar curvature is lordosis (the hollow back).
Your vertebrae are largest at the lower end of your back, where your lumbar spine joins your pelvis at the lumbosacral joint. A lot of extra weight bears down on this area (your whole trunk, arms, neck and skull, and of course anything you carry, all exerting downwards pressure through the back). The higher up the spine you go, the smaller the vertebrae become, as the load on each successive bone lightens.
They also come in different shapes, depending on their differing functions. Just as your lumbar vertebrae carry maximum weight, the thoracic vertebrae are the attachment points for your ribs and breastbone, and the complex that forms your shoulder-blades and collarbones. Higher up, cervical bones not only support your head, their shapes are also adapted for nodding, looking up, turning or tilting to left and right, rolling clockwise or counter-clockwise, and other movements.
The basic architecture of nearly all vertebrae is pretty much the same. There is a “body”, a thick oval slab, which supports the other parts of the structure, as shown in Figure 2.
Fig. 2: Basic shape of the body of the vertebra
Protruding at an angle from the back of this body are two small bony projections, the pedicles, pointing away from each other, and at the end of each pedicle, angled in towards the centre is a further bony protrusion, the lamina. The laminae join in the middle, and the space between pedicles and laminae forms an arch-shaped passage attached to the back of the vertebral body. (The shape is a little like the “A-frame” used in prefabricated buildings.) As your vertebrae are stacked one on top of the other, each with its own little arched passage, the joined-up passages form a tunnel, which contains and protects your spinal cord.
On each side of the “A-frame”, where the pedicle joins the lamina, there is a peg of bone protruding out sideways. These pegs are the transverse processes. Where the laminae merge at the rearmost point of the “A-frame” there’s a similar peg, the spinous process. The sketch in Figure 3 shows the general shape as seen from above. There are two upper and two lower surfaces, known as facet joints, where the vertebra contacts its upper and lower neighbours. Figure 4 represents the vertebra seen diagonally from the right front.
Fig. 3: Diagram of vertebra with pedicles, laminae and processes
Fig. 4: Vertebra with processes and facet joints.
Above and below the body of the vertebra is a thick, fibrous disc, the intervertebral disc, which works like a tough, malleable cushion to absorb shock and facilitate movement (see Figures 5 and 6). It allows your back to tilt forwards, backwards and sideways, as well as rotating to either side. Specific sections of spine are adapted to each of these purposes, and their vertebrae are shaped accordingly.
Fig. 5: Intervertebral disc
Fig. 6: Vertebrae with intervertebral discs
The vertebrae are linked to each other by three long, tough continuous ligaments, one at the front, which stops you bending over backwards too far, one attached to the back of each vertebral body, and another connecting all the tips of the spinous processes, all protecting the intervertebral discs from too much pressure in forwards or backwards bends. These three ligaments run the entire length of the spine, but there are many other, shorter ones, connecting the spinous or transverse processes and the laminae of each bone to the others.
A great many muscles connect the spinous and transverse processes to others above and below, allowing you to flex, extend, rotate or incline the back – yet others move the neck, head, shoulder-blades and ribs, and stabilise the entire structure. There are muscles linking the transverse processes not only to the vertebra above, but stretching further to the one above that, and even to the one above that, and some reaching as far as six vertebrae further up, all the way up the line…
Your spine is an extraordinary piece of engineering, somewhat resembling a cantilever bridge. It has to be heavy enough to deal with the weight of you and all the things you do, yet light enough to be mobile, flexible enough for movement, yet stable enough to protect and support the trunk and its organs, and tough enough to resist injury. It’s an impressive piece of work; yet another amazing part of the miracle that is you and your dancing life.
©Jeremy Leslie-Spinks
References
1. Calais-Germain B. (1993, 2007). Anatomy of Movement (revised ed.). Seattle, WA: Eastland Press, Inc.
2. Grossman G. (2015). Dance Science Anatomy, Movement Analysis, Conditioning. Hightstown, NJ: Princeton Book Company, Publishers.
3. Solomon R, Solomon J, Cerny Minton S. (2005, 1990). Preventing Dance Injuries (2nd ed.). Champagne, IL: Human Kinetics.
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