The main privilege of a person is upright posture. It became possible due to radical changes in the support and movement system, which includes the skeleton and muscles. All its departments have the best functional fitness for the vertical position of the body. This led to the release of the upper limb from participation in the movement of the body and its inclusion in various types of physical activity: retention and precise manipulation of objects and tools, the performance of purely human actions. Examples illustrating them are the ability to write, play musical instruments, draw, sew, knit, etc.
In this article we will focus on the structural features of the belt of the upper extremities, which includes the scapula and clavicle. Where is it located, what functions does it perform, what is its role in the musculoskeletal system of a person?
Place of collarbone in human skeleton
The bone entering the belt of the upper extremities is connected to the sternum with the help of the sternoclavicular joint. The lateral part of the clavicle is connected with the shoulder blade - acromion. At this point, the bone has a tuberous, rough surface for firmly attaching the shoulder muscle using the ligament system. To better understand what the clavicle is, consider the structure of one of the departments of the musculoskeletal system - the upper limb belt.
Clavicle as part of the upper limb belt
In order for the bones of the hand to be connected to other parts of the body, the human skeleton has a special section consisting of paired bones - triangular scapula and clavicle. In the structure of his body, the shoulder girdle, including the collarbone, already have vertebrates, starting with representatives of the Overclass of Pisces. It is quite developed in mammals that use their forelimbs in the process of capturing prey or moving by the method of brachiation (for example, in gibbons). Let’s further consider where the collarbone is and what part of the body it is. It has the form of the Latin letter S, connected with its sternum to the sternum, and the exterior with the scapula, for strength these joints are strengthened by ligaments.
At the moment of the vertical movement of the shoulder, the bone rotates around its axis like a key in a keyhole, hence the name - clavicle. Next, we dwell on its functions in the body.
The role of the bones of the upper limb belt in the system of support and movement
Earlier, we determined the place in the human skeleton where the collarbone is located. Anatomically, it is connected to the shoulder blade and sternum, providing support on which the humerus is attached . The structure of such a connection-lever in the best way contributes to an increase in the amplitude of hand movements. The clavicle also serves as the transmission link for mechanical action from the upper limb to the chest and spine. Several important muscles are attached to it, playing both a static and a dynamic role. The anatomy of the clavicle, the functions that are inherent in it, are due primarily to the internal structure. Let's get acquainted with it in more detail.
Bone tissue histogenesis
In the embryonic period of development, cell types such as fibroblasts, chondroblasts and osteoblasts form from the middle germinal leaf. Of these, such tissues that form the organs of the musculoskeletal system, such as connective, cartilage and bone, develop in the future. To answer the question: what is the clavicle in terms of internal structure, we recall that in the human skeleton there are bones that are called mixed. They are formed by elements of different origins. For example, the clavicle is formed partly from connective tissue that underwent osteogenesis without the formation of cartilage, partly from chondrocytes, in which the process of ossification took place.
What muscles are attached to the upper limb belt
All movements of the human body are carried out in the coordinated work of the skeleton bones and muscles attached to them by ligaments. So, to move the upper limb in the shoulder joint, the deltoid muscle contracts. Recall where the collarbone is located in a person, and find out its role in the movement of the hand. It is to the upper part and the front edge of this bone that enters the belt of the upper extremities that the deltoid muscle is attached. The trapezoid and sternocleidomastoid muscles are attached to the posterior edge of the clavicle using the trapezoid and conical ligaments.
The first of them statically holds the upper back in an upright position, the second provides turns and tilts of the head and can participate in respiratory movements.
How is the formation of clavicle in embryogenesis?
To clearly understand what the clavicle is, consider the mechanism for laying the bone tissue. The formation of the skeleton in the embryo begins from 5-6 weeks of fetal development and is a process of ossification. And the first bone that forms in osteogenesis is the collarbone. She will be one of the last fully formed, whose ossification lasts up to 21 years of human life. Its appearance begins with the unification of cells of the middle germ layer into groups anatomically connected with the capillaries of the embryo.
The division and differentiation of primary mesenchymal cells ends with the appearance of fibers consisting of fibroblasts. Then they accumulate a collagen-like substance, osseomucoid, in their composition and take the form of fibers. Osteoblasts appear around them - the primary cells of bone tissue that begin to produce minerals. Fibrous strands are saturated with salts, lose their elasticity and become stiff. Mature osteocytes form, and the capillaries are surrounded by bone plates that look like concentric rings and cylinders. The outer layer of fibroblasts turns into the periosteum, covering the clavicle.
Pathology of the bones of the upper limb belt
Above, we determined what the clavicle is and how it is formed in the process of human embryonic development. Clavicle abnormalities arise due to a violation of normal osteogenesis in the embryo and are caused by a hereditary predisposition of the person.
So, hypoplasia, which has symptoms of underdevelopment or complete absence of the clavicle in the upper limb belt, is due to a defect in the gene located in the autosome and in a dominant state. Such a violation as cranio-clavicular dysostosis is manifested by anomalies in the development of the facial and brain parts of the skull and is accompanied by pathological mobility of the shoulder blades and clavicles, as well as dislocations in the acromioclavicular joint. Quite often, pathologies of the upper limb belt are recorded together with other abnormalities in the structure of the skeleton, for example, in the Goltz syndrome, abnormalities in the development of the dental apparatus, excessive melanin synthesis and trophic skin lesions are combined with collarbone hypoplasia.
In this article, we examined the structure, functions, and possible pathologies of the clavicle, which is an integral part of the belt of the upper limbs of the human skeleton.