HUMAN SKELETON

The human skeleton consists of both fused and individual bones supported and supplemented by ligaments, tendons, muscles and cartilage. It serves as a scaffold which supports organs, anchors muscles and protects organs such as the brain, lungs and heart. The biggest bone in the body is the femur in the thigh and the smallest is the stapes bone in the middle ear. In an adult, the skeleton comprises around 30-40% of the total body weight and half of this weight is water.
Fused bones include those of the pelvis and the cranium. Not all bones are interconnected directly: there are three bones in each middle ear called the ossicles that articulate only with each other. The hyoid bone, which is located in the neck and serves as the point of attachment for the tongue, does not articulate with any other bones in the body, being supported by muscles and ligaments. Early in gestation, a fetus has a cartilaginous skeleton from which the long bones and most other bones gradually form throughout the remaining gestation period and for years after birth in a process called endochondral ossification. The flat bones of the skull and the clavicles are formed from connective tissue in a process known as intramembranous ossification and ossification of the mandible occurs in the fibrous membrane covering the outer surfaces of Meckel's cartilages. At birth, a newborn baby has over 300 bones, whereas on average an adult human has 206 bones. The difference comes from a number of small bones that fuse together during growth, such as the sacrum and coccyx of the vertebral column.

The axial skeleton is formed by the Vertebral column, the Rib cage and the skull. The axial skeleton transmits the weight from the head, the trunk and the upper extremities down to the lower extremities at the hip joints and is therefore responsible for the upright position of the human body. Most of the body weight is located in back of the spinal column which therefore have the erectors spinae muscles and a large amount of ligaments attached to it resulting in the curved shape of the spine. The 366 skeletal muscles acting on the axial skeleton position the spine, allowing for big movements in the thoracic cage for breathing and the head. Conclusive research cited by the American Society for Bone Mineral Research demonstrates that weight-bearing exercise stimulates bone growth. Only the parts of the skeleton that are directly affected by the exercise will benefit. Non weight-bearing activity including swimming and cycling has no effect on bone growth.

There are many differences between the male and female human skeletons. Most prominent is the difference in the pelvis owing to characteristics required for the processes of childbirth. The shape of a female pelvis is flatter more rounded and proportionally larger to allow the head of a fetus to pass. Also the coccyx of a female's pelvis is oriented more inferiorly whereas the man's coccyx is usually oriented more anteriorly. This difference allows more room for a developing fetus. Men tend to have slightly thicker and longer limbs and digit bones, while women tend to have narrower rib cages, smaller teeth, less angular mandibles, less pronounced cranial features such as the brow ridges and external occipital protuberance and the carrying angle of the forearm is more pronounced in females. Females also tend to have more rounded shoulder blades.