The bones, ossa, together form the skeletal bone. Together with the joints, this is called the locomotor apparatus - the passive musculoskeletal system. It moves by using the active musculoskeletal system, the muscles (musculature).
The skeleton has four functions:
Provides the body with sturdiness and shape
Provides protection for soft tissue
Enables muscles to be attached
Forms blood cells
If the skeleton is not sufficiently strong , malformations can occur and the body then changes in shape. Insufficient skeletal strength (e.g. due to osteoporosis) can lead to bone fractures more quickly.
The skeleton also protects more vulnerable parts. This is how our brains are protected in the cranial cavity, the heart and lungs in the thoracic cavity and the bladder and uterus in the pelvic cavity.
The muscles need a solid support where they can attach themselves to. They generally run from one section of bone to another and are attached to it via tendons that ensure a very secure connection.
Where two pieces of bone meet, they form a joint. Contraction (shortening) of a muscle causes the relevant joint to move.
Insufficient skeletal strength (e.g. due to osteoporosis) can lead to bone fractures more quickly. Two or more bones may be connected with each other through fibres, cartilage or joints. With fibrous connections, practically all movement is absent (seam connection between the skull bones, but also the connection between e.g. radius and ulna). With cartilaginous joints there is only limited movement (ribs/breastbone, pubic bones). Basically, it is only joints that allow movement of two pieces of bone in relation to each other. The most solid joint that can occur is a complete fusion; e.g. the sacrum (5 fused vertebrae) or the pelvic bones (fusion of iilia, ischium and pubic bone).
Bone tissue is a special form of connective tissue. It is pressure-resistant and can withstand intense tensile forces. It is made up of collagen fibrils (30%), calcium salts (60%) and water (10%). The collagen fibrils and the calcium salts provide a bone with its firmness.
Bones vary in shape, depending on their function and location. We are familiar with the long bones (e.g. humerus, thighbone). The inside of these bones contains yellow bone marrow that is very rich in fat. There are also the flat bones such as the ribs, sternum, shoulder blade and ilium. It is especially in these bones that red bone marrow occurs where blood cells are produced. We also have short bones (in our hands and feet) and irregular bones (vertebrae).
Macroscopically there are two distinctly built sections to our bones. The surface is usually made of solid material (substantia compacta), especially in the short and
flat bones and in specific sections of the long bones there is a sponge-like network (substancia spongioza).
If we take a closer look at a bone, we will see that it is covered nearly everywhere by a tough membrane. This is the bone membrane or periosteum. Blood vessels that deliver blood supply run from this bone membrane into the bone.
Despite its hard nature, bone tissue (even in adulthood) is highly dynamic. Due to pressure and tensile forces, bone is constantly being renewed by building up and breaking down the bone tissue. Bone is able to recover well after a bone fracture, and while a body is growing, bones undergo major changes in shape.