Musculoskeletal system

The connections of the bones - articulatio.

Development of the bones connections.
On 6-7 th week between the cartilage bones models occurs the concentration of mesenchyme. Then development of the bones connections goes by two ways:
1) from the mesenchyme forms fibrous or cartilaginous tissue (development of the uninterrupted bones connection);
2) liquefaction of the mesenchyme (development of the interruptions bones connection).

Classification of the bones connections:
I. Uninterrupted connection - synarthrosis:
1.1. Fibrous connection:
1.1.1. Syndesmosis - connection of the bones by ligaments and membranes.
1.1.2. Connection of the bones skull.
1.1.3. Herniation –zubo alveolar connection.
1.2. Cartilage connection - synchondrosis;
- Constant;
- Temporary;
- Symphysis.
1.3. Bone connection - synostosis
II. Discontinuous connection - diarthrosis;

Bone tissue develops from the mesenchyme. At the end of the 1st month of fetal development are formed clusters of mesenchyme, which form the membrane models for future bones. This is stage of development of membranous bones. From 2nd month cells begin to produce chondrin and comes cartilage stage. With 6-7 weeks begins bone stage of development of bones. But the bones of the cranial vault, the bones of the face, medial plate of pterygoid process, the middle part of the clavicle in their development have no cartilage stage and are called primary bones. With the development of bone by the direct (membranous) ossification in young connective tissue (mainly in the center of the future bone) appears one or more points of the ossification. Point of the ossification consists of the osteoblasts (young bone cells ), placed in the form of beams. Beams grow, forming a skeletal grid, in loops of which are located bone marrow cells and blood vessels. Osteoblasts produce intercellular substance in which are deposited salts of calcium. Gradually osteoblasts transformed to osteocytes (mature bone cells), are formed the inner and outer plates of compact bone substance, sponge substance, surface layers of connective tissue are converted to the periosteum. The bones of the trunk, limbs, skull base develop on the site of cartilage and are called secondary bones. With the development of the bone by indirect ossification, the bone formation can occur on the periphery of the cartilage - perichondral ossification, or from the middle of cartilage - enchondral ossification.

Ossification of long tubular bones in the area of diaphysis carried by perichondral and enchondral way. The first point of ossification appears in the center of cartilage model of bone on the 8th week of embryogenesis.

Musculoskeletal system is formed by bones, bones connections, skeletal muscles. Musculoskeletal system ensures movement in space and support of the human body. Bones and the bones connections make passive part of the musculoskeletal system, bones perform the function of levers. Muscles - is an active part the musculoskeletal system, during the muscles contraction, perform body movements (changing the position of the bones). Musculoskeletal system is studied by such sciences as: osteology, myology, and arthrology , that are united in osteoartromiology.

Classification of bones:
- Tubular bones - have a body - diaphysis (diaphysis) and end - epiphysis. Between the diaphysis and the epiphysis is the "growth zone" - metaphysis, by which the bone grows in length. Tubular bones can be long and short. Long tubular bones perform locomotor function, short - supporting.
- Trabecular bones are short, have a shape of an irregular cube.
- Flat bones are wide, are involved in the formation of a body cavity serve a protective function.
- Mixed bones are complex. Have elements of the flat and trabecular bones.
- Pneumatic bones - have a cavity filled with air.


Every bone is an independent organ. Living human bone contains of 50% water, 28.15% of organic substances and 21.85% of inorganic compounds (compounds of calcium, phosphorus, magnesium, etc.). Macerated (bleached, dried) bone consists of 1/3 organic substances and 2/3 of inorganic chemicals. With the predominance of organic substances in the bone (children), the bone is more flexible; with the predominance of inorganic substances (older people) - the bone is crisp. The bone is composed of bone tissue. The outer layer of the bones are formed by compact substance (substantia compacta), which consists of lamellar bone tissue through which pass thin bone tubules (some of which are parallel to the surface of the bone, others - perpendicular). Bone tubules is a continuation of feeding channels (candles nutricia), which open on the surface of the bone. Through feeding channels occurs power supply and innervation of the bone, because through them pass arteries, veins and nerves. The structural unit of the bone is osteon or Haversian system.

The muscles and fascia develop from myotomes, including from the dorsal part of myotomes develop deep back muscles, from the ventral part of myotomes - the muscles of the front and literal surface of the body (muscles of the chest, abdomen, neck). The diaphragm develops from the sixth cervical myotome. At the end of 4-th week of fetal development, muscles of limbs develop from buds of limbs. From buds of mesoderm the anterior of 4 lower cervical and first thoracic myotomes develop muscles of the upper limbs. Chewing and mimic muscles, some muscles of the neck, the muscles of the soft palate, throat, larynx develop from the mesoderm of gill arches.

The bones of the head and neck play the vital role of supporting the brain, sensory organs, nerves, and blood vessels of the head and protecting these structures from mechanical damage. Movements of these bones by the attached muscles of the head provide for facial expressions, eating, speech, and head movement.

The skull consists of 22 cranial and facial bones, which, with the exception of the mandible, are tightly fused together. The skull encases and protects the brain as well as the special sense organs of vision, hearing, balance, taste and smell. Attachment points for the muscles of the head and neck are located on the exterior surfaces of the skull and allow for important movement like chewing, speech, and facial expressions. Teeth are rooted into deep sockets in the mandible and maxillary bones. The upper portions of the digestive and respiratory tracts are also housed within the hollow oral and nasal cavities of the skull.

A collection of 22 bones, the skull protects the all-important brain and supports the other soft tissues of the head. During fetal development, the bones of the skull form within tough, fibrous membranes in a fetus’ head. As these bones grow throughout fetal and childhood development, they begin to fuse together, forming a single skull. The only bone that remains separate from the rest of the skull is the mandible, or jaw bone. Early separation of the bones provides the fetal skull with the flexibility necessary to pass through the tight confines of the birth canal. During childhood development, the skull bones remain somewhat separated, allowing for growth of the brain and skull. Upon reaching maturity, our skull bones fuse to produce a rigid protective shell for the soft nervous tissue of our brain.

The bones of the chest and upper back combine to form the strong, protective rib cage around the vital thoracic organs such as the heart and lungs. The rib cage also anchors the bones of the head, neck, shoulders, and arms to the trunk of the body. Powerful muscles that move the head and arms attach to these bones as well. The bones of the chest and their joints also support the upper body’s weight.

Stretching down the midline of the trunk from the base of the skull to the coccyx, the spine plays an extremely important role in our bodies as it supports the upper body’s weight; provides posture while allowing for movement and flexibility; and protects the spinal cord.

The spine, also known as the vertebral column or spinal column, is a column of 26 bones in an adult body – 24 separate vertebrae interspaced with cartilage, and then additionally the sacrum and coccyx. Prior to adolescence, the spine consists of 33 bones because the sacrum’s five bones and the coccyx’s four do not fuse together until adolescence.

The costal cartilage is a set of hyaline cartilage bands that attach the medial end of the seven true ribs to the lateral border of the sternum (breastbone). Costal (cost- = rib) cartilage also connects the three superior false ribs to the sternum, but these false ribs are attached indirectly by way of the seventh true rib’s cartilage band.