The Teres Major is a small circular muscle that runs along the lateral edge of the scapula. It forms the lower boundary of both triangular and quadrangular spaces. And also, it is sometimes called the “lat’s little helper” because of its synergistic action with the latissimus dorsi.
The large round muscle is a thick muscle of the shoulder joint. Moreover, it extends from the bottom of the scapula to the proximal shaft of the humerus. Unlike the small round muscle, the large round muscle does not attach to the shoulder joint capsule. Thus, it is not considered part of the rotator cuff muscle.
Teresa Major and Minor
Despite similar names, Teresa Major has different actions and innervation than Teresa the Younger. Basically, the large round muscle is the thick ovoid muscle of the shoulder. However, it is mainly responsible for the arm’s internal rotation and contributes to the static posture and swinging of the arm.
Origin and Insertion
The large circular muscle originates from the posterior surface of the lower angle of the scapula and the lower part of the lateral edge of the scapula. Initially, the power is easily palpable and felt like a soft tissue structure in the lower corner of the scapula.
Muscle fibres run spirally (torsionally) parallel to the fibres of the latissimus dorsi muscle. They converge on a single tendon that attaches to the humerus’s interlabial groove (medial lip).
The posterior part (scapular part) of the large round muscle is covered with the small round and infraspinatus muscles. The anterior part of the large round muscle corresponds to the subscapularis muscle.
The lower edge of the teres major round muscle is parallel to the upper border of the latissimus dorsi muscle. Along with the small round muscle, the large round muscle forms the posterior axillary fold. The adjacent fibres of these two muscles can grow together in some people. Sometimes their muscle bellies or attached tendons even fuse.
Teres Major Features
The crucial function of this muscle is to produce arm movements in the shoulder joint. By contract, it pulls the humerus backward (extension) and rotates it medially towards the trunk (internal rotation). In addition, it helps stabilize the shoulder joint.
Laterally with the pectoralis major and latissimus dorsi, the Tereus Maximus can pull the trunk upward (through adduction) when its brachial attachment is in place. In addition, it helps stabilize the shoulder joint. That is why it is also called the mountaineering muscle.
Basic Facts about the Large Round Muscles
|Origin||Inferior angle and inferior part of the lateral border of the scapula|
|Insertions||Intertcubular sulcus (medial lip) of the humerus|
|Innervation||Lower subscapular nerve (C5-C7)|
|Blood supply||Thoracodorsal branch of the subscapularis and artery and the posterior circumflex brachial artery|
|Function||Extension & internal rotation of the humerus (arm)|
The large round muscle is relatively prone to the development of trigger points. These are local permanent hypertensive zones with rigidity (myofascial pain syndrome).
Inadequate stretching before exercise, injuries (such as falling onto the shoulder), and micro-trauma from chronic inappropriate tension are common causes. Symptoms include local pain that may radiate to the side of the shoulder on palpation and difficulty in abducting and raising the arm.
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