Basic Bone Structure
Bones are organs composed of hard living tissue providing structural
support to the body it’s scaffolding. It is a hard matrix
of calcium salts deposited around protein fibers. Minerals make
bone rigid and proteins (collagen) provide strength and elasticity.
In an adult, bone engages in a continuous cycle of breaking
down and rebuilding. Bone absorbing cells called Osteoclasts
break bone down and discard worn cells. After a few weeks the
osteoclasts disappear and Osteoblasts come to repair
the bone. During the cycle calcium is deposited and withdrawn
from the blood.
The Periosteum, a fibrous membrane, covers the outside
of bone. This membrane is rich with capillaries, which are responsible
for nourishing bone.
The outer layer of bone is called Cortical bone. Eighty
percent of skeletal bone mass is cortical bone. Cancellous
bone (also called trabecular bone) is an inner spongy structure
that resembles honeycomb, which accounts for 20% of bone mass.
This spongy meshlike bone is designed for strength similar
to steel rods within a concrete structure. The inner bone cavities
contain bone marrow where red blood cells are produced.
The shape of bone is described as long, short, flat, or irregular.
They are further classified as Axial or Appendicular. Axial
bones are protective. For example, spinal vertebrae act to protect
the spinal cord. Appendicular bones are the limbs. Although
there are many shapes and sizes of skeletal bone, the bones
that make up the spinal column are unique.
(1) Vertebral Body (2) Spinous Process
(3) Articular Process (4) Transverse Process
(5) Foramen (6) Pedicle