On its back is the teres major muscle, whose name means much "large round muscle". Its origin lies at the lower edge of the scapula (in the inferior scapulae) and it attaches to the humerus. The approach of the teres major muscle is located on the crista tuberculi minoris on the front of the bone, which also attaches to the large dorsal muscle (latissimus dorsi muscle).
The teres major muscle belongs to the skeletal musculature and consists of striated fibers, whose pattern goes back to the structure of the muscle. Within the skeletal muscle, the teres major muscle can be assigned to the shoulder muscles. According to some definitions, it belongs to the rotator cuff, while others regard it only as a secondary stabilizer of the cuff. The deliberate control of the teres major muscle is based on motor areas of the brain and passes through sympathetic nerve fibers.
Nerve tracts that supply the teres major muscle pass through the spinal nerves of the neck. The commands for relaxation and relaxation come mainly from the subscapular nerve, which also supplies the subscapular nerve with neuronal stimuli.
Less commonly, the teres major muscle also receives nerve signals from the thoracodorsal nerve, which belongs to the brachial plexus and also controls the great dorsi muscle (latissimus dorsi muscle), or from the axillary nerve, which belongs to the same network of nerves, and mainly to the deltoid muscle and the musculus teres minor is responsible.
The tendon of the teres major muscle is 5 cm long and connects to the humerus via a bursa (bursa synovialis), whereby the bursa reduces friction. The muscle surrounds a shell of connective tissue; its internal structure consists of muscle fiber bundles, each of which combines several muscle fibers. The muscle fibers form the muscle cells, but they are not differentiated from each other like other body cells. Instead, they form a continuous tissue with many cell nuclei. Myofibrils run lengthwise through the muscle fibers, their sections (sarcomeres) consisting of actin / tropomyosin and myosin filaments.
At the transition from a motor nerve fiber to the muscle is the motor end plate. The electrical action potential from the axon of the nerve cell triggers the release of neurotransmitters here as in an interneuronal synapse.
These messenger substances (often acetylcholine) cause the endplate potential on the muscle, which spreads through the cell membrane of the muscle cell, channels in the cell (T-tubules) and the guidance system of the sarcoplasmic reticulum. The sarcoplasmic reticulum releases calcium ions in response to the electrical potential, whereupon the thread-like myofilaments interlock, thereby shortening the muscle. When the nerve no longer excites the muscle, the electrical endplate potential also disappears, the calcium ions remain in the sarcoplasmic reticulum, and the muscle relaxes.
The task of the teres major muscle is to move the arm in certain directions; He participates in the internal rotation, which turns the arm inwards, and the retroversion, which pulls him backwards. Even with movements of the upper arm towards the body (adduction), the large round muscle is active. These movements also involve the latissimus dorsi muscle. In addition, the teres major muscle together with the pectoralis major muscle and the latissimus dorsi muscle stabilizes the shoulder.
As part of the rotator cuff, the teres major muscle may be affected by conditions affecting this anatomical structure. The rotator cuff tears the tendon that connects the muscle to the bone.
The rupture causes pain and hinders the mobility of the arm-shoulder-part. As one of the stabilizing muscles of the cuff, the teres major muscle is of great importance in rehabilitation after injuries of the rotator cuff, since it can relieve the damaged structure. This case is common in impingement syndrome when the tendon of the shoulder muscle is pinched.
In myofascial pain syndrome, the muscle hardens as a result of a persistent state of tension. The tension on the teres major muscle can affect the mobility of the shoulder muscle and thus the mobility of the arm. In addition, the hypertension causes pain, especially during movement and pressure on the affected area. Such a trigger point arises for example from overloading and fine cracks in the muscle. Movement pain can also be due to other causes, such as bursitis. Depending on the severity, it manifests in weaker or stronger pain, the area may be locally warmed or swollen. There may also be fluid in the tissue.
Occasionally, the control of the teres major muscle does not originate from the subscapular nerve, but from the axillary nerve. This nerve runs along the axilla near the humerus - in a location that is very vulnerable to fractures. If the humerus breaks, the surrounding tissue may be damaged and the axillary nerve may be affected. Lesions on the nerve are also possible when dislocating the shoulder (dislocation). Regardless of the cause, injuries to motor nerve fibers that control the teres major muscle can restrict the muscle's ability to move. This also applies to the other two nerves (subscapular nerve and thoracodorsal nerve).Tags: