The musculoskeletal system of the human body is a real miracle of nature. It supports all parts of the body in the right position, protects vital organs and provides amazing mobility to the entire body. The belt of the upper extremities is responsible for fastening the hands to the axial skeleton.
Clavicle and shoulder blade construction
The composition of the belt of the upper extremities implies a construction of two shoulder blades, two clavicles and the skeleton of the limb itself. It is the belt of the upper limbs that creates the shape of the shoulders of a person. The hands are connected to the body with the shoulder blades and collarbones, which form the belt of the upper extremities. The shoulder blades are located at the top of the back, have a triangular shape, they are connected to the spine and ribs with the help of muscles. The shoulder blade is paired with the clavicle, and the clavicle is connected to the sternum and ribs. The clavicle has the form of a curved bone extending between the sternum and the external angle of the scapula.
The skeleton of the upper limb belt is built of the following parts:
- 2 clavicles;
- 2 blades;
- humeral bones;
- radial bones;
- ulnar bones;
- wrists;
- metacarpal bones;
- phalanx of the fingers.
Upper limb function
The main function that the belt of the upper limbs of a person performs is to create a strong and maneuverable support for the hands. Unlike the pelvic girdle, it is not rigidly connected to the axial skeleton. The main bones of the belt of the upper extremities: the clavicle, which forms the usual joint with the sternum, and the scapula is connected with the bones of the body by powerful muscles. As a result, the shoulders actively participate in the movements of the hands, increasing the amplitude and, accordingly, the work efficiency.
The bones of the belt of the upper extremities of a person have a structure like that of the skeleton of vertebrates, and consist of 3 sections - the shoulder, forearm and hand. The muscles associated with this belt strengthen the shoulder joint and are responsible for most of the movements of the hands. Shoulder - a wide plate in the form of a triangle, located behind the chest from the back, is part of the belt of the upper extremities. It has a flat depression of the shoulder joint, in which the head of the humerus is placed. The shoulder joint is relatively unstable, it provides the maximum range of motion, but is sensitive to dislocations and other injuries.
The main bones of the hands
The humerus is represented in the form of a long tubular bone of the belt of the upper extremities, two fairly long ulnar and radius bones are attached to it. The humerus forms the ulnar joint with both bones, and the hand connects to only one of them - the wrist joint. The ulna is located on the inside. All bones of the hand are connected to each other thanks to the joints.
The main ones are:
- brachial;
- wrist band;
- ulnar.
The joints are very diverse in movement, with active mobility, which led to the transformation of the front limb, that is, the arm, during evolution into an organ of labor. The ulnar and radial bones are more stable than the humerus, respectively, the movements are less free. Finger joints are even stronger. According to the structure of the skeleton, the arm and leg are very similar. Their main difference is the device of the brush, in which the thumb is separate from the rest, which allows the hand to make grasping movements. Between the wrist and metacarpal bone of this finger is the only saddle joint in the human body, the movement in which is much freer than at the base of the first toe.
The structure of the elbow joint
The belt of the upper extremities includes the joint of the elbow, which consists of two parts: block-shaped and spherical. The first connects the protrusion of the humerus with the ulnar notch, it also provides flexion-extensor movements with the hands. The spherical part connects the head of the humerus with the radial fossa. This allows you to twist the forearm. In general, the joint is quite stable due to the large joint surface and strong ligaments. The radius is the main one in the forearm. It forms a joint with the wrist. The ulna together with the radius forms the ulnar joint.
The structure of the shoulder joint
The belt of the upper extremities includes the shoulder joint. The shoulder joint is the most mobile in the human body. Its almost flat cavity on the scapula is articulated with the hemispherical head of the humerus. This device allows you to freely rotate your hand in all directions. The bone turns almost in a circle, up, down. Such mobility has its drawbacks, due to the fact that the strength of the connection is reduced, dislocations often occur in this joint. The second joint is formed by the scapula and collarbone. It often happens sprain when falling on an outstretched arm or when hitting the front of the shoulder.
Wrist
This part of the arm has a rather complicated structure. The brush consists of 3 sections, which, in turn, have 27 bones. At the base of the palm are 5 metacarpal bones and 8 bones of the wrist. The skeleton of the fingers themselves comprise 14 phalanges, 2 bones in the thumb and 3 in each of the four. The hand has a highly specialized structure. In infants, they are only indicated, gradually forming, they will be clearly visible only by the age of seven, and their ossification ends much later, by about 10-13 years. By the same period, the ossification of the phalanges of the fingers ends.
Ligaments and muscles of the upper limb belt
Since the shoulder joint is quite mobile, and the shoulder girdle is not rigidly connected with the axial skeleton, the muscles of the upper limb belt have a special function. Muscles connect the arm to the body and act as shock absorbers. The deltoid muscle is the largest and strongest in the shoulder, connects the scapula and the humerus. It is thanks to her that the hand rises and moves forward and backward.
The rotational cuff consists of four smaller muscles:
- papillary;
- supraspinatus;
- small round;
- subscapular.
They also control the rotation of the arm and strengthen the shoulder joint.
The main muscles of the belt of the upper limb
The upper limb has a pair of main muscles: biceps and triceps, which form a pair of antagonists: if one contracts, the other relaxes. Biceps, or biceps, goes from the scapula to the radius. If you bend your hand hard, you can feel it well. The triceps, or triceps muscle of the shoulder, connects the scapula with the ulna. It is not so noticeable, but larger than the biceps. Moving, they act as one muscle group. For example, while raising the forearm, the biceps contract, the muscle that pulls the forearm to the shoulder. At the same time, triceps, the extensor muscle, which allows you to straighten your arm again, is stretched.
Extensors and flexors
The complex movements of the wrists and hands are provided mainly by the coordinated work of many muscles passing in the forearm. These are flexors and extensors. The flexors bring the palm closer to the forearm and squeeze the fingers. They pass along the inside of the arm. The extensors straighten the hand and fingers, bringing their back surface closer to the forearm. To unclench a palm and take an object with it, coordinated work of 35 muscles of a forearm and a brush is required. In addition, the muscles of the forearm deflect the brush left and right, rotate it, turn the palm of the hand and fix the wrist and fingers in the desired position. The subtle movements of the fingers are controlled by the bone’s own muscles, going from the bones of the wrist to the base of the first phalanges. The work of the remaining phalanges is provided by the long tendons of the flexors and extensors located in the forearm.
Age and prevention of bone aging
The human upper limb belt needs anti-aging prophylaxis. With age, bone strength decreases and the risk of fractures increases. Age-related loss of bone tissue is almost irreversible, but they can and should be prevented or significantly slowed down. Overstrain of the muscles of the shoulders and back is fraught with a very painful condition. People who spend whole days at the computer and desktop are often stooped or in a hunched posture. From here arises the stiffness of constantly tense muscles and stretching of the muscles of the shoulders and back, which threatens the occurrence of painful muscle nodes and tension headaches.
It is necessary to strengthen the belt of the upper extremities, namely the muscles of the shoulders and back, through exercises that straighten the chest and unload the muscles and ligaments. Shoulder mixing and breeding, as well as shrug, are very helpful. Physical education alleviates pain, strengthens muscles and bones, increases the flexibility of the body, and therefore both mobility and human ability to work.