Skeletal system

The muscoskeletal system’s passive part is the skeleton, the active part being the skeletal muscle. The bones are joined together by joints and moved by muscles. The muscles are connected to the bones by tendons. In areas where large amounts of friction occur, the tendons are covered in tendon sheat. Muscles do not work separately, but in groups.

Bone structure

Skeleton

Skull

Axial skeleton

Appendicular skeleton

Bone connections

Joints

Bone structure and types

Bones are mainly made up of bone tissue. Its most important inorganic component is calcium. 4/5th of the body’s calcium content is stored in the bones. Its organic components are the protein fibres. The inorganic components ensure solidity and rigidity, while the organic components provide flexibility for the bones; both characteristics are needed due to the intense strain.

Bones can be categorized according to their shape into long, flat, and irregular bones.

Long bones are elongated in shape and have medullary cavities inside. Examples are the upper- and lower arm bones, the thigh bone, and the bones of the shin.
Flat bones include most of the skull bones, the pelvis, the scapulae, the sternum and the ribs.
Irregular bones include the vertebrae, the metacarpal bones in the hand and the metatarsal bones in the foot.

Osteoporosis

Bone structure

The exterior of bones is covered by periosteum, which houses veins and nerves, the veins entering the interior part of the bone. The periosteum plays an extremely important part in bone sustenance and in healing injuries.

Under the periosteum is the compact bone, followed by the small bone plates and trabeculae that make up the trabecular bone. The trabecular bone is able to transform depending on its load. Long bones also each have a medullary cavity inside, which contains the yellow bone marrow, composed mostly of adipose tissue. Flat and irregular bones have no medullary cavity, but their trabecular bones contain the red bone marrow, which plays an important part in haematogenesis.

Bone structure, types

The skeleton

The human skeleton is made up of approximately 206 bones. The skeleton not only supports the body, but also protects the interior organs, while also providing storage for calcium, as well as playing an important role in haematogenesis. The main parts of the skeleton are the skull, the axial skeleton, the appendicular skeleton and the girdles.

The skull

The skull’s two main parts are the neurocranium, which protects the brain, and the viscerocranium, which is located at the front. Both are made up of a number of different bones. The skull is connected to the spinal column by the occipital area, allowing movement. The bones of the skull usually can not be moved separately, with the exception of the jaw, which is connected to the neurocranium by a joint.

Connection of the skull and the spine

The axial skeleton

The axial skeleton is made up of the spinal column (which consists of the vertebrae), the ribs, and the sternum. The spinal column is the skeleton’s axis, and is composed of 32-34 vertebrae, part of which have mobile connections in between them, and part of which are merged. The cavities inside vertically aligned vertebrae together form a protective channel, in which lies the spinal cord. The 12 pairs of ribs articulate with the vertebrae in the back, and with the exception of two pairs of false ribs, are connected to the sternum by a cartilaginous connection. The vertebrae, the ribs, and the sternum together form the chest.

Side view of the spinal column Posture mistakes Location of the spinal marrow inside the spinal column

Appendicular skeleton, girdles

The girdles’ job is to connect the limbs to the axial skeleton. The girdle connecting the arm is the shoulder girdle, which is made up of the scapulae and the collarbones. The legs are connected to the trunk by the pelvic girdle. The arm bones are the humerus (which is connected to the girdle), the radius, the ulna, the 8 tiny carpal bones (which make up the wrist joint), the metacarpal joints (which form the frame of the palm), and the phalanges. In the skeletal system of the leg, the femur, which is the longest bone in the body, is connected to the pelvic girdle, followed by the tibia and the fibula, which together form the shin. The bones of the tarsus are all small in size with the exception of the calcaneus, and make up the ankle area. The skeletal frame of the

Flatfoot Skeleton

Bone connections

The bones of the skeleton can connect in numerous ways. Part of these result in mobile connections, the rest in connections where the joints cannot move relative to each other.

The pelvic bone and the sacrum, which can be found at the base of the spinal column, are the result of multiple bones merging, therefore their constituting bones cannot be moved relative to each other. The boundaries of the unions are difficult to notice.
The bones of the skull are similar, but here the stitches are clearly visible. This is also an immobile connection; however, it does not prevent skull growth.
Cartilaginous connections allow a small amount of movement, such as between the ribs and the sternum, but the vertebrae are also connected to each other with cartilaginous vertebral discs. The spinal column’s apparent good mobility is the result of the many small intervertebral opportunities for movement
The type of connection between two bones that allows for the widest range of motion is the joint.

Joint structure

Joints are mobile connections between bones, in which two or more bones are connected to one another. The surface of the articulating bones is covered with smooth cartilage. The bone ends are connected by the joint socket. The cells located in the socket’s interior layer produce synovial fluid, which prevents bone surfaces from touching, and decreases friction between the moving bones. The joint ligaments connect the bone ends, and enhance the solidity of the joint. The shape of the articulating bones’ surface determines the possible directions of movement.

Bone fracture, pulled muscles and sprains

Joint types

Movement in the joints is determined by the articulating bones and the shape of the articular surface, as well as by the joint socket and the ligaments.

Spheroidal joints (such as the thigh joint and the shoulder joint) can move in any direction.
Hinge joints can only contract and extend (eg. the knee and elbow joints, and the interphalangeal joints).
Saddle joints (eg. the wrist joint, the metacarpal bones and the interphalangeeal joints) allow for the connecting bones’ contraction and extension, as well as abduction and adduction.

Joints and other bone connections