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Our bones are not at all like the bones you may have seen in labs, on a skeleton, or even after a non-vegetarian
meal. Usually people see or notice only the "hard" parts of a bone. This is the mineralized bone, which is
generally made up of calcium salts that are deposited between the collagen fibers of the bone. What is
missing is the mesh of collagen, which is much more leather-like than hard. In living bone there is a
significant portion of both collagen and calcium salts. The mineral salts help us tolerate compression
of the bone while the collagen helps us resist tension that would bend or break the bone.
If the bone was made only of mineral salt and was subjected to extreme pressure, it would snap the way an
old tree branch breaks: cleanly. However, healthy, especially young bone, with a high degree of collagen
meshing, breaks more like a living branch of a tree. If you have ever tried to snap off a living branch
you know that is just bends, crumpling one side while fraying the side away from the pressure.
[1]
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Examined closely, the inside of our bones appears porous. This sponge-like scaffolding allows the bones to
be light and yet incredibly strong. The spongy-looking part is called "trabecular" bone and it is more
elastic than the harder outer skin of the bone, which is called "cortical" bone. Trabecular bone is more
active, more subject to bone turnover, to remodeling. The ratio of trabecular to cortical bone varies
throughout the body depending upon the need. For example, the bones of the rib are not weight bearing
and so they have much higher trabecular content. Our leg bones have much more cortical bone.
[See image to the right]
Cartilage is similar in makeup to bone but has a different ratio of collagen to mineral salts and other
components. The cartilage in our nose, for example, has much more hydration [2] than our bones. The
cartilage in our ears is even more flexible thanks to the presence of more elastin fibers. In our
intervertebral disks we have fibrocartilage with a higher proportion of collagen to chondroitin.
This allows the cartilage in our spines to have greater weight-bearing support than we would find
in the cartilage in our ears.
Cartilage supports tissues and provides a degree of structure and firmness. Bones do exactly the same
thing, but to a different degree. Of significant interest to the student of yoga are the three kinds
of the "other" connective tissues: tendons, ligaments, and the fasciae. Each of these has different
degrees of flexibility, caused by their different makeup. We have already looked at fasciae, so now
let's look at tendons and ligaments.
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1 -- If this is hard to imagine, go find a green branch and try to break it cleanly. It can't be done.
Only old, dried-out branches snap in half. The same difference is found in young and old bones.
2 -- Thanks to chondroitin-sulfate.
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