The human skeleton is composed of:
- Bones: to support all internal structures of the body, provide a site for muscles to attach and insert into, to give rigidity to the body, to provide a site for haematopoeisis, and to provide a major site of calcium storage (about 97% of all calcium in the body).
- Cartilages: to join bones to other bones or muscles in the form of tendons and ligaments. Hyaline cartilage cushions joints but is not considered part of the skeleton.
- Joints: hinge regions that allow bones to move relative to each other, e.g. the tibia & fibula can move relative to the femur about the knee joint when extending or flexing the leg.
The structure of the human skeleton can be seen in Figure 1 (anterior view) and Figure 2 (posterior view). The arms (upper limbs) and legs (lower limbs) are common sites of fracture and the anterior view shows that the clavicle articulates with the humerus by way of the scapula, providing the only bone attachment to the upper limb. The arm consists of the humerus, and the forearm, the radius and ulna, which are united at the elbow joint. At the wrist joint, the radius and ulna articulate with various wrist (carpal) bones, which in turn articulate with the metacarpals and phalanges. These are numbered ordinally; for example, the metacarpal of the "index finger" is known as the second metacarpal. The phalanges can be split into a proximal, middle and distal phalanx for digits 2 - 4 (the index finger to the little finger), and into a proximal and distal phalanx for the thumb. The lower limb has several analogous structures. The humerus, for example, can be likened to the femur (thigh bone), the heaviest bone in the body, and the radius and ulna are comparable to the tibia and fibula of the lower leg. These latter two bones articulate with tarsal bones at the ankle joint, and these in turn articulate with the first to fifth metatarsal bones. As in the hand, proximal, middle and distal phalanges can also be found, but this time in all the digits (toes). The posterior view shows how ribs - also commonly fractured - continue posteriorly to articulate with the facets of the vertebrae. The vertebrae, which communicate the spinal cord and can have devestating consequences such as paralysis if fractured, can be divided into, in descending order, seven cervical vertebrae (known as C1 - C7), thoracic vertebrae (T1 - T12), lumbra vertebrae (L1 - L5) and sacral vertebrae (S1 - S5).
Figure 1: Anterior view of the human skeleton. Figure 2: Posterior view of the human skeleton.
Courtesy of Wikimedia Commons. (http://upload.wikimedia.org/wikipedia/commons/4/4e/Human_skeleton_back_en.svg and http://upload.wikimedia.org/wikipedia/commons/4/4e/Human_skeleton_back_en.svg) - please click on these links for larger versions of the images.
Continue to: Gross anatomy of selected bones.