Dominic Stone
The scapula, commonly referred to as the shoulder blade, is a bone that sits above the rib cage in the upper back. The shoulder musculature not only has the task of moving the joint but is also responsible for keeping it healthy. The scapula can move in six directions, and each movement is produced by specific primary muscles. The scapulohumeral muscles are muscles that connect the scapula to the humerus. The seven scapular muscles include the teres major, latissimus dorsi, deltoid, supraspinatus, infraspinatus, teres minor, and subscapularis. The teres major and the latissimus dorsi cause arm extension, adduction, and medial rotation. The deltoid muscles cover and shape the shoulder, enabling arm abduction, flexion, extension, and medial and lateral rotation.
| Characteristics | Values |
|---|---|
| Number of scapular muscles | 7 |
| Muscles | Deltoid, Teres Major, Latissimus Dorsi, Supraspinatus, Infraspinatus, Teres Minor, Subscapularis, Coracobrachialis |
| Deltoid Muscle Parts | Anterior, Lateral, Posterior |
| Teres Major Origin | Lower one-third of the lateral scapula |
| Latissimus Dorsi Origin | Spinous processes of the thoracic vertebrae T7 to T12, crests of sacrum and ilium, and ribs 9 to 12 |
| Trapezius Muscle Location | Nuchal region and dorsal part of the thorax |
| Trapezius Muscle Insertion | Upper border of the crest of the spine and medial border of the acromion |
| Serratus Anterior Insertion | Medial border of the costal surface |
| Coracobrachialis Origin | Medial part of the tip of the coracoids process |
| Triceps Brachii Parts | Long Head, Lateral Head, Medial Head |
| Rhomboid Muscles | Rhomboid Major, Rhomboid Minor |
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What You'll Learn
Teres major, latissimus dorsi, and coracobrachialis muscles
The scapula, or shoulder blade, is a bone that sits above the rib cage in the upper back. The scapulae can move in six directions, and each movement is produced by specific, primary muscles. The latissimus dorsi, teres major, and coracobrachialis muscles all play a role in scapular movement and shoulder function.
The latissimus dorsi is a broad, flat muscle that occupies most of the lower posterior thorax. It is considered a respiratory accessory muscle and is part of the superficial layer of extrinsic back muscles. This muscle can pull the inferior angle of the scapula in various directions, producing movements on the shoulder joint, including internal rotation, adduction, and extension of the arm. It is also active in moving the trunk forward and upward when the upper extremities are fixed overhead, as in climbing. The latissimus dorsi also assists in holding the scapula against the thorax during upper limb movements and is essential for smooth and fluid upper extremity movements.
The teres major is a small muscle that runs along the lateral border of the scapula and is sometimes referred to as "lat's little helper" due to its synergistic action with the latissimus dorsi. It is one of the seven scapulohumeral muscles that act around the glenohumeral joint to facilitate shoulder movement. The teres major works together with the latissimus dorsi to extend, adduct, and internally rotate the shoulder. A tear in the teres major muscle can cause a sudden sharp pain in the shoulder, upper arm, and armpit, and this pain intensifies with physical activity.
The coracobrachialis muscle is not one of the most prominent arm muscles and does not play a significant role in moving the arm. However, it provides support for certain movements, including flexion, adduction, internal rotation, and shoulder stability. It attaches to the front of the shoulder joint and the upper arm bone, running down the inside of the upper arm to the midpoint. The coracobrachialis can become tight from certain activities and may be a hidden source of shoulder or arm pain.
Overall, the latissimus dorsi, teres major, and coracobrachialis muscles all contribute to the complex movements of the scapula and shoulder joint, with the latissimus dorsi and teres major playing more prominent roles in scapular motion and the coracobrachialis providing additional support and stability.
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Trapezius and rhomboid muscles
The scapula, or shoulder blade, is the bone that sits above the rib cage in the upper back. The scapulae can move in six directions, and each movement is produced by specific, primary muscles. The trapezius and rhomboid muscles are two such muscle groups that influence scapular movement.
The trapezius muscle is located in the nuchal region and the dorsal part of the thorax. It originates from the external occipital protuberance, the nuchal ligament, and the spinous processes of the seventh cervical vertebra and all the thoracic vertebrae. Its bundles converge toward the shoulder and are inserted at the lateral third of the posterior margin of the clavicle and at the upper lip of the posterior margin of the spine of the scapula. The trapezius muscle influences the movements of the scapula and indirectly helps the shoulder in adduction and flexion.
The rhomboid muscles are made up of two functionally similar muscles: the rhomboid minor and the rhomboid major. The rhomboid minor originates from the nuchal ligament and the spinous processes of the seventh cervical and first thoracic vertebrae. It extends obliquely in an inferolateral direction and inserts into the base of the medial end of the spine of the scapula. The rhomboid minor partially overlaps the superior portion of the rhomboid major. The rhomboid muscles overlie the deep (intrinsic) muscles of the back and are covered by the trapezius muscle, except for a small triangular region over the inferior border of the rhomboid major.
The main action of the rhomboid muscles is scapular retraction around the scapulothoracic joint. This involves a simultaneous sliding of the scapula superiorly and medially along the trunk, which rotates the glenoid cavity inferiorly and drops the shoulder girdle. By opposing excessive scapular protraction, the rhomboids help to maintain correct posture when sitting, standing, and walking. Additionally, the contraction of the rhomboids fixes and stabilizes the scapula, providing an anchor point for the movement of the upper limb.
Both the trapezius and rhomboid muscles are important for the movement and stability of the scapula, and they work together to facilitate shoulder movements and maintain proper posture.
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Rotator cuff muscles
The scapula, or shoulder blade, is the bone that sits above the rib cage in the upper back. The shoulder joint is formed where the scapula meets the head of the humerus, the bone of the upper arm. The scapula can move in six directions, and these movements are produced by specific primary muscles.
The rotator cuff is a group of four distinct muscles and their tendons, which provide strength and stability to the shoulder complex. These muscles are the supraspinatus, infraspinatus, teres minor, and subscapularis. They are also referred to as the SITS muscle, with reference to the first letter of their names. These muscles arise from the scapula and connect to the head of the humerus, forming a cuff around the glenohumeral joint. The rotator cuff muscles are deeper muscles and are very active in the neuromuscular control of the shoulder complex during upper extremity movements. They are essential players in almost every type of shoulder movement, including flexion, abduction, internal rotation, and external rotation.
The rotator cuff muscles are responsible for stabilising the glenohumeral joint by compressing the humeral head against the glenoid. The tendons of these muscles blend with the joint capsule and form a musculotendinous collar that surrounds the posterior, superior, and anterior aspects of the joint. This arrangement is important as it prevents the humerus from sliding inferiorly through the unprotected part of the joint, which is the most common cause of shoulder luxations.
The rotator cuff muscles receive their vascular supply mainly via the suprascapular artery, the subscapular artery, and the posterior circumflex humeral artery. The suprascapular artery supplies the supraspinatus and infraspinatus muscles, while the subscapular artery gives vascular supply to the subscapularis muscle.
Injuries to the rotator cuff are common and can occur at any age. Dysfunction of the rotator cuff muscles can lead to shoulder pain, impaired function, and a reduced quality of life. Diagnosis of rotator cuff tendinopathy can be done through clinical tests, X-rays, and MRI scans, with MRI being the most effective method for evaluating rotator cuff injuries.
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Deltoid muscles
The deltoid muscles are a group of large, triangular intrinsic shoulder muscles that cover the front, side, and back of the shoulder joint. They get their name from their shape, which resembles the inverted Greek letter delta. These muscles are responsible for several functions, including arm abduction, flexion, extension, and stabilization of the shoulder joint.
The deltoid muscle has three parts: anterior, lateral, and posterior. These different parts have distinct functions and work together to facilitate various movements. The anterior deltoid is primarily responsible for flexion, internal rotation, and horizontal adduction. To stretch this muscle, the actions are reversed, resulting in extension, external rotation, and horizontal abduction of the shoulder joint.
The posterior deltoid, often referred to as the rear delts, assists in moving the arm backward. They connect to the flat surface of the shoulder blade and are engaged during activities like pitching a baseball. The primary function of the posterior deltoid is extension, external rotation, and horizontal abduction. Similar to the anterior deltoid, reversing these actions stretches the muscle, resulting in flexion, internal rotation, and horizontal adduction of the shoulder joint.
The lateral region of the deltoid muscle is multipennate, while the anterior and posterior portions are unipennate. When these three parts contract simultaneously, they assist in abducting the arm past 15 degrees. The anterior and posterior deltoids also play a stabilizing role during abduction, while the lateral deltoid helps raise the arm from 15 to 100 degrees.
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Pectoralis major and latissimus dorsi muscles
The pectoralis major is a prominent chest muscle that acts on the shoulder joint. It is a fan-shaped muscle that lies underneath the breast tissue in the anterior chest wall. The pectoralis major is divided into three parts: the clavicular part, the sternocostal part, and the abdominal part. All three parts converge laterally and insert onto the greater tubercle of the humerus. The main function of this muscle is the adduction and internal rotation of the arm in the shoulder joint.
The clavicular part originates from the anterior surface of the medial half of the clavicle. The sternocostal part, which is larger than the clavicular part, originates from the anterior surface of the manubrium and body of the sternum, as well as the anterior surface of the superior six costal cartilages. The abdominal part is the smallest part and originates from the anterior layer of the rectus sheath.
The pectoralis major has two heads: the clavicular head and the sternocostal head. The clavicular head can be tested by transversely adducting the arm at the glenohumeral joint against resistance. The sternocostal head can be tested by adducting the arm at the glenohumeral joint against resistance.
The latissimus dorsi muscle forms the posterior pillar and the posterior wall of the axillary cavity. It covers the lower and lateral sides of the back (lumbar region) and the lateral part of the chest.
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Frequently asked questions
The scapula, commonly known as the shoulder blade, is a bone that sits above the rib cage in the upper back.
There are seven scapular muscles that move the scapula.
The seven scapular muscles are the teres major, deltoid, supraspinatus, infraspinatus, teres minor, subscapularis, and coracobrachialis.
The teres major and the latissimus dorsi cause arm extension, adduction, and medial rotation. The deltoid muscles cover and shape the shoulder, enabling arm abduction, flexion, extension, and medial and lateral rotation. The supraspinatus assists the deltoid in arm abduction. The infraspinatus causes lateral arm rotation. The teres minor also causes lateral arm rotation and extension. The subscapularis causes medial arm rotation. The coracobrachialis helps with arm flexion and adduction.
The trapezius and serratus anterior muscles work together to influence the movements of the scapula and help the shoulder with adduction and flexion.
