The humeral girdle consists of three bones: the clavicle, scapula, humerus (upper arm bone), as well as muscles, ligaments and tendons. The shoulder joints are movable joints between the bones of the shoulder. The muscles and joints of the shoulder allow it to move in a given range of motion. The muscles of the shoulder and shoulder girdle are responsible for the movement of the scapula, humerus and clavicle. In addition, these muscles form the shoulder, shoulder joint and armpits (armpits). For example, the rounded contour of the shoulder joint is formed by the deltoid muscle. Anatomically, it is a set of various fibers whose work is coordinated by the central nervous system.
The human shoulder is the upper part of the arm with muscles and bone enclosed between the shoulder and elbow joints. The upper border of the shoulder is the transverse line of the lower edge of the pectoralis major muscle, pectoralis major muscle, and broad back muscle. The lower border runs higher (2 transverse fingers) of the condyles of the humerus. The shoulder muscles are located on the front and rear surfaces of the humerus. The front muscle group is called biceps (in Latin - musculus biceps brachii) or biceps muscle. The back muscle group is triceps (in Latin - musculus triceps brachii) or triceps.
The elastic and elastic tissue (skeletal, or it is also called striated), from which the shoulder muscles are composed, is able to contract due to nerve impulses. Due to these properties of muscle tissue, elbow joint movements occur, and triceps and biceps are responsible for these movements. In addition, both of these muscles determine the shape of the shoulder, which directly depends on the degree of development and fatness of the muscles. Due to the subcutaneous fat layer, the reliefs of muscles are smoothed out in children and women, and the shoulder has a look close to the regular cylinder. In men with developed muscles, the shoulder volume is greater in the upper part than in the area bordering the elbow.
The vernacular name of the biceps of the shoulder - biceps - comes from two Latin words: bis, which is translated as twice, and caput, which means the head. Biceps (two bundles of muscles) has two heads connecting in the middle of the shoulder into a common muscle abdomen. The long head is attached to the scapula (supra-articular roughness of the cavity) with the initial tendon. The short head also starts from the scapula (coracoid process). The biceps are attached to the upper part of the forearm with the final tendon, into which the common abdomen passes. The main function of this muscle is to bend the elbow joint of the arm. It is innervated by the musculocutaneous nerve.
The colloquial name of the triceps brachii - triceps - also comes from two Latin words, the first of them (tri) means three, and the second (caput), as described above. This large muscle is approximately 2/3 of the muscle mass of the arm and is responsible for the extension (straightening) of the arm in the elbow joint, also fixes the elbow joint when the forearm and hand are used for subtle movements, for example, when writing. It consists of three bundles of muscle tissue that begin with three heads (long, median and lateral), and converge and combine in one tendon of the elbow. Classically, it is believed that all three heads of the triceps brachii are innervated by the radial nerve. However, there are research results showing that innervation can occur by the axillary nerve branch .
The forearm of a person is the part of the hand that is located between the elbow joint and the wrist (otherwise called the wrist). The forearm consists of muscles and two bones (ulnar and radial). Muscle tissue is formed from four layers of muscles that belong to the anterior group, as well as two layers of muscles of the posterior group. The result of their work is the movement of the hand (including the phalanx of the fingers) and the wrist. In general, the muscles of the shoulder and forearm provide a wide variety of movements of the shoulder, forearm, and hands.