|Picture 1. Right Lateral View of the Spine, taken of the Atlas of the Bones by Marieb.|
Due to its relationship with gravity, the mature, healthy spine adopts two kinds of curvatures. A primary curve is always convex and is called like that because the whole human spine is curved like a "C" in newborn. Secondary curves are concave and are a result of being a Homo erectus.When babies start to crawl and raise their heads to look at things, they start developing the cervical curve. At this point, crawling babies start strengthening their lower backs through adopting a "cobra-like" pose which we will call from now on "baby backbends" (Picture 2). Cute toddlers just stretch theirselves to look up, and while doing so, their lower back acquires the sufficient strength to be able to sit down in an upright position, thus generating a secondary lumbar curve. I just think it's lovely how wise is nature, I heard once, although I am not sure, that if babies are not taught to sit down or to stand up, they actually have the whole instructions to do it by themselves in due time when their backs are strong enough!!! What do you think?
Wrapping it all up, the human spine has two primary curves: the toracic spine, and the sacrum; and two secondary curves, the cervical and lumbar spine.
|Picture 2. Baby backbend, taken from http://wyoga.com/wordpress/wp-content/uploads/2011/04/1281127__baby_boy__3.jpg|
Picture 3. Posterior view of the spine.
As you can see in both, picture 1 and 3, the vertebrae of the different regions have different shapes, the lumbar vertebrae are wider and thicker than those at the cervical region. This is due to the amount of weight they carry and to their relationships to other bodily structures. Let's see more pictures about it.
|Picture 4. The cervical Spine|
On picture 4. we can see the shapes of the cervical vertebrae, there are 7 of them. They have no vertebral body, but they are wide, they only support the head and neck. The first and second cervical vertebrae (C1 and C2) are called Atlas and Axis respectively (see picture 5).
|Picture 5. Atlas and Axis (C1 and C2)|
Atlas (like the mythological greek that carried the world in Hercules's times) articulates with the skull. Such a joint permits you to move your head as if you were saying yes (flexion-extension movement). Axis, is articulated to atlas through an extension called "Odontoid (Tooth shaped) process" (see picture 5). This odonto-atalantic joint makes possible for your head to rotate left and right like when saying no. if you put your hands behind your neck, and walk your fingers downwards in between the superior edge of the shoulder blades, you will feel a prominent bone, this one is the spinous process of the seventh cervical vertebra (see picture 6). The cervical spine is a concave curve and is not protected by any bone structure, therefore, the muscles in the neck are used to protect it from fracture and tough movements.
|Picture 6. Vertebra Prominens or C7|
Taking good care of the neck is something everyone should pay attention to. The mean weight of the head lies around 4.5 or 5 kg, that is, somewhere around 8% of your total body weight!!!
I once heard a chiropractor saying that around 90% of the people who visit him have a condition called rectified neck! As a ball park estimation, I would take it that over half of the world population have rectified necks. A neck goes rectified when the cervical curve begins to disappear. The reason I talk about this is because rectified necks can carry less weight than a normally concave neck!! The loss of this concavity is related to the western posture of sitting down to read, work, and pay attention. also when you read in bead, your neck goes straightened. Neck care goes beyond yoga, seldomly do we realize that we are either overstretching or overextending it!
Asanas like head and shoulder balance where the neck is used powerfully must always be approached carefully. Early practitioners must not attempt to do the full poses before their bodies are ready, even if the rest of the class is upside-down.
The toracic vertebrae are just below the cervical forming a convex curve. There are 12 of them and they are articulated to the ribs, thus forming the rear wall of the toracic cavity. The toracic back is stabilized by the ribcage, this means movility around this area tends to be more limited. Toracic vertebrae have a body and a formal spinous and transverse processes as can be seen in picture 7. I will describe all about the function of these processes in the second part of this section where I will talk about the muscles of the back.
|Picture 7. Toracic Spine|
Kyphosis is the condition in which the toracic convex curve is overdone. People with xyphosis are also caled hunchbacks. Fortunately, most of the people who develop a hunch later in their lives can be alerted of this way before it is too late. Early simptoms include closed and tight chest muscles, shoulders tight and fallen towards the front, and the shifting the neck forward among others (see picture 8). Working on strenghtening the upper and lower backs, loosening and bringing back the shoulders as in savasana, rooting the feet on the ground, and pulling the ears away from your shoulders can help prevent kyphosis.
|Picture 8. Kyphotic spine.|
The last section is called the lumbar region. Lumbar vertebrae have very big bodies as they carry the whole weight of the body in them (no wonder why usually they go herniated). There are 5 lumbar vertebrae, and they articulate with the sacrum which is a group of fused vertebrae (See picture 9). The possition of the lumbar must be mildly concave.
|Picture 9. Lumbar Spine|
Too much of a concave curve is called Lordosis and can take the intervertebral disks to herniate among many other things. (See piecture 10)
|Picture 10. Lordotic spine.|
It is the lumbar spine the weakest link in the column for the modern, erect-walking human being. I often find it surprising that in this technological era where new advances and discoveries happen almost everyday, people suffer of lower back problems more than ever. The cause? Well, it is difficult to say it is this or that. Each case is very particular, however today's society is more stressed and sedentary. When we are not sitting down incorrectly at work, we are walking incorrectly or driving somewhere while sitting incorrectly. If you look attentively at your friends sitting down in a chair or couch at a reunion. you will discover that most of them are sitting down collapsed on the lumbar! (This is what many people call "sitting down with the kidneys") When you sit this way, both your toracic and lumbar spines are flexed due to a) a posterior tilt (extension of the pelvis) which moves your lumbar into a convex curve, and b) a forward flexion of the upper back in order "to reach the computer".
The position of your lumbar depends mainly on the position of your pelvis.
Check picture 11, see the different pelvis positions. An extended pelvis (Posterior tilt) produces the collapsation of the lower back, while a hyperflexion caues lordosis (Anterior tilt). The position of the sacrum can hint you on how you are holding your lumbar. Check how the sacrum looks on picture 12, the name sacrum was given because since it is the last bone to decompose, therefore it was considered holly.
|Picture 11. Different pelvic positions.|
|Picture 12. Sacrum|
If you think of the pelvis as a bucket of water, an anterior tilt will spill the water in front of you, while a posterior tilt will spill the water behind you. In a neutral position, the pelvis must not be tilted, however, hinging the pelvis on top of the femur joints is very important in certain asanas. In a forward bend, in order no to compress the intervertebral disks too much, an anterior tilt, or flexion will help you keep your back straight for most of the time, thus protecting the intervertebral disks. A posterior tilt, or "backbend paddling" of the pelvis will be of big aid during backbends and arches helping you stretch the back, creating space between the vertebras, elongating the spine, and avoiding the collapsation of the sacrum into the lumbar.
Try practicing lying on the floor the different possitions of the pelvis as shown in the following picture.
|Picture 13. Checking the positions of the pelvis.|
I think this is enough anatomy for the day. Next time we will talk about the muscles of the back, the bandhas and standing in Tadasana. Hope you enjoyed it and that it made you direct your attention to how you are holding your back.
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