Skeleton

From ArticleWorld

The skeleton is the part of the body of an animal the gives it its physical structure. Most animals have parts of the skeleton compartmentalized in such a way that the animal can move independently. For example, vertebrates have a calcified bony skeleton that is made of multiple bones, attached by ligaments and made mobile by muscular attachments.

Types

In comparative anatomy, there are three types of skeletons. Humans and vertebrates have internal calcified bony structures that have internal musculature that allows for skeletal movement. The muscles, bones and ligaments work together to make a firm support that is also easily moveable.

Other animals have an exoskeleton, where the structure is visible to the outside and the muscles are beneath it. Exoskeletons do not allow for growth of the organism and so are sometimes shed by the organism in order for another larger skeleton to take its place.

Some lower animals, like worms, have no bony skeleton but have a hydrostatic skeleton that is based on water providing enough pressure within the organism to create a malleable structure. The worm moves by changing the pressure in the various water compartments so that sometimes it is long and thin, while, at other times, it is thicker in places.

Anatomy

The human endoskeleton consists of over 200 separate bones that are attached to each other by connective tissue and cartilage that form joints. The skull is a single bony structure with sutures marking where several fetal bones joined together. The spinal column begins at the base of the skull and extends to the buttocks, ending in a flat bone, known as the sacrum. Ribs are partly bony and partly cartilaginous and together protect the lungs and heart from injury. The pelvis is a large bone that provides structure for the attachment of the leg bones.

In humans, the upper and lower extremities are similar in that they join to the body through a “ball-in-socket” joint. Articulated long bones extend to the ends of the extremities, where multiple bones make up the two hands and the two feet. Some mammals have bones as part of their tail; however, humans do not.