5. BONES AND JOINTS

The skeleton of a person consists of over than 200 bones. They unite together with the help of joints and ligaments. 32 or 34 bones are unpaired, the others are paired.

23 bones form the skull, 32-34 bones form the spinal column, 25 bones form ribs and the breastbone, 64 bones form the skeleton of the upper extremities, and 62 bones form the skeleton of the lower extremities.

The bones of the skeleton are formed by bony and cartilaginous tissues, related to connective tissue. The bones consist of cells and intercellular substance.

Bone classification Tubular bones

These are composed of spongy and compact substance forming a tube with a marrow cavity. They perform all three functions of the skeleton (support, protection and movement). Long tubular bones (arm bone, forearm bones, thigh bone, and leg bones) are supports and long levers of movement. Short tubular bones (phalanges) are short levers of movement.

Spongy bones

These bones consist mainly of spongy substance covered with a thin layer of compact substance. Long (ribs and sternum) and short (vertebrae, carpal, tarsal) spongy bones are distinguished. The group of spongy bones also includes sesamoid bones, i.e. bones which resemble sesame seeds in shape, hence their name (the knee cap, the pisiform bone, the sesamoid bones of the fingers and toes). The sesamoid bones are located close to the joints, take part in their formation, and promote movements in them but are not joined directly to the bones of the skeleton.

Flat bones

- The flat bones of the skull (frontal and parietal) perform a function that

is mainly protective (membrane bones). - The flat bones of the girdles (shoulder blades, pelvic bones) perform

supportive and protective functions. Their structure is primarily spongy