The human skeleton contains over 200 bones.
Types of bones
All bones of the skeleton are divided into four types according to their structure, origin and functions: tubular (humerus, ulnar, radial, femur, tibia, fibula) are long bones in the form of a tube that have a canal inside with yellow bone marrow. Provide fast varied limb movements.
Spongy (long: ribs, sternum; short: bones of the wrist, tarsus) – bones, mainly consisting of a spongy substance, covered with a thin layer of compact substance. They contain red bone marrow, which provides the function of hematopoiesis.
Flat (scapula, skull bones) – bones, the width of which prevails over the thickness to protect the internal organs. They consist of plates of a compact substance and a thin layer of spongy substance.
Mixed – consist of several parts with different structure, origin and function (the vertebral body is spongy bone, and its processes are flat bones).
Types of bone connection
Different types of bone connections provide the functions of the skeletal parts.
A fixed (continuous) connection is a fusion or bonding of connective tissue to perform a protective function (connection of the bones of the roof of the skull to protect the brain).
A semi-movable connection with the help of small cartilaginous discs forms bones that perform both protective and motor functions (connections of the vertebrae with intervertebral discs, connection of the sternum and ribs).
Due to the joints, the movable (discontinuous) connection has bones that ensure the movement of the body.
Joints and their connections
Different joints provide different directions of movement.
The joint consists of:
- articular surfaces of articulating bones;
- joint bag;
- articular cavity;
- articular (synovial) fluid.
The articular surfaces correspond to each other in shape and are covered with hyaline cartilage. The bursa forms an airtight cavity with synovial fluid. This promotes sliding and protects the bone from abrasion.