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The pectoral region is located on the anterior chest wall and contains four muscles that exert a force on the upper limb: the pectoralis major, pectoralis minor, serratus anterior, and subclavius. The pectoralis major is the largest and most superficial muscle in the pectoral region and is responsible for flexion, adduction, and internal rotation of the humerus. It also abducts and medially rotates the upper limb and draws the scapula anteroinferiorly. The pectoralis minor lies underneath the pectoralis major and stabilises the scapula by drawing it against the thoracic wall. The serratus anterior is located more laterally in the chest wall and holds the scapula against the ribcage. The subclavius is a small muscle located directly underneath the clavicle, providing some protection to the underlying neurovascular structures. So, do the pectoral muscles abduct the limb? Yes, the pectoralis major and minor muscles both contribute to the abduction of the limb.
| Characteristics | Values |
|---|---|
| Location | Anterior chest wall |
| Muscle Groups | Pectoralis major, pectoralis minor, serratus anterior, subclavius |
| Muscle Shape | Thick and fan-shaped |
| Muscle Attachments | Sternocostal head, clavicular head |
| Muscle Innervation | Lateral and medial pectoral nerves |
| Muscle Function | Adduction, medial rotation of the upper limb, scapula stabilisation |
| Muscle Movement | Abduction, flexion, adduction, internal rotation of the humerus, elevation and depression of the thorax bones |
| Muscle Injury | Pectoralis major tendon rupture, long thoracic nerve palsy |
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What You'll Learn
- The pectoralis major is the largest muscle in the pectoral region
- The pectoralis minor lies underneath the pectoralis major
- The serratus anterior holds the scapula against the ribcage
- The subclavius muscle affords minor protection to underlying neurovascular structures
- The pectoralis major can be tested by adducting the arm at the glenohumeral joint
The pectoralis major is the largest muscle in the pectoral region
The pectoralis major is a paired, superficial muscle located on the anterior surface of the thoracic cage. It has a broad origin, which is divided into three parts: clavicular, sternocostal, and abdominal. 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. When the arm is in the anatomical position, the pectoralis major acts as a strong adductor and internal rotator of the humerus at the shoulder joint. The clavicular portion of the muscle can flex the humerus up to 90 degrees in a horizontal plane, while the sternocostal portion can produce the antagonistic movement and extend the humerus back to the anatomical position.
The pectoralis major is active during deep or forced inspiration, assisting in breathing. It also facilitates the act of inspiration when acting from the humeral attachment. This muscle is innervated by the lateral and medial pectoral nerves, which stem from the brachial plexus.
The pectoralis major can be tested by placing the subject's arm in horizontal abduction, with the elbow extended and the shoulder in lateral rotation (palm upward). The tendon of the pectoralis major at the sternum should not be found to be unduly tense, even with maximum abduction of the arm, unless the muscle is short. The length of the pectoralis major can be tested by placing the subject in a supine position with the knees bent and the low back flat on a table.
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The pectoralis minor lies underneath the pectoralis major
The pectoralis minor is a thin, triangular muscle that lies underneath the pectoralis major, the most superficial muscle in the pectoral region. The pectoralis major is a thick, fan-shaped muscle that constitutes the bulk of the chest muscles, lying underneath the breast tissue. It is composed of two heads: the clavicular and the sternocostal. The clavicular head originates from the anterior surface of the medial clavicle, while the sternocostal head originates from the anterior surface of the sternum, the superior six costal cartilages, and the aponeurosis of the external oblique muscle. The pectoralis major is responsible for adducting and medially rotating the upper limb, as well as drawing the scapula anteroinferiorly.
The pectoralis minor, on the other hand, originates from the third to fifth ribs near the corresponding costal cartilages. Its fibres pass upward and laterally to insert into the medial border and superior surface of the coracoid process. The primary nerve supply to the pectoralis minor comes from the medial pectoral nerve, with additional innervation from the lateral pectoral nerve. The pectoralis minor is crucial in stabilising the scapula by pulling it downward and anteriorly against the thoracic wall. It also plays a role in respiration, aiding in raising ribs 3-5 during deep inspiration and expanding the thoracic cavity.
Together, the pectoralis major and minor form the anterior wall of the axilla region. The pectoralis minor is clinically significant and serves as a surgical landmark due to the structures located beneath it. The pectoralis minor is also associated with the serratus anterior and intercostal muscles, the ribs, and several neurovascular and lymphatic structures.
The pectoral region, located on the anterior chest wall, contains four muscles that exert force on the upper limb: the pectoralis major, pectoralis minor, serratus anterior, and subclavius. These muscles work together to produce various movements and stabilise the scapula. The serratus anterior, for example, helps to hold the scapula against the ribcage, while the subclavius provides protection to the underlying neurovascular structures.
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The serratus anterior holds the scapula against the ribcage
The serratus anterior is a thin, fan-shaped muscle that originates on the superolateral surfaces of the first to eighth or ninth ribs at the lateral wall of the thorax. It is located more laterally in the chest wall and forms the medial border of the axilla region. The main part of the serratus anterior lies deep under the scapula and the pectoral muscles. It is easily palpable between the pectoralis major and latissimus dorsi muscles.
The serratus anterior also acts with the upper and lower fibres of the trapezius muscle to sustain upward rotation of the scapula, which allows for overhead arm movement. When the shoulder girdle is fixed, all three parts of the serratus anterior muscle work together to lift the ribs, assisting with respiration. This muscle is also used in respiratory distress, acting as an accessory inspiratory muscle.
The serratus anterior is trained indirectly in all anterior deltoid exercises. It is also exercised in chest exercises that involve scapular protraction, such as isometric exercises like the plank and straight-arm plank.
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The subclavius muscle affords minor protection to underlying neurovascular structures
The pectoral region is located on the anterior chest wall and contains muscles that exert a force on the upper limb. These include the pectoralis major, pectoralis minor, serratus anterior, and subclavius. The pectoralis major is the most superficial muscle in the pectoral region. It is thick and fan-shaped, covering much of the superior portion of the anterior thorax. The pectoralis minor lies underneath the pectoralis major and both muscles form part of the anterior wall of the axilla region.
The subclavius is a small, triangular muscle in the anterior thorax located directly underneath the clavicle and running horizontally. It originates from the junction of the first rib and its costal cartilage and inserts onto the inferior surface of the middle third of the clavicle. The subclavius is innervated by the nerve to the subclavius, a branch of the brachial plexus. Its main function is to stabilize the clavicle during movements of the shoulder girdle and arm.
The subclavius also affords minor protection to the underlying neurovascular structures. For example, in the event of a clavicular fracture or other trauma, the subclavius helps to prevent injuries to the adjacent neurovascular structures. This is due to its ability to stabilize the clavicle and prevent its dislocation at the sternoclavicular joint.
In addition to its protective role, the subclavius may also play a role in regulating the output of kinetic energy of the upper extremity's movement rather than acting solely as a muscle of stabilization.
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The pectoralis major can be tested by adducting the arm at the glenohumeral joint
The pectoralis major is a thick, fan-shaped muscle that constitutes the bulk of the chest muscles, lying underneath the breast. It is one of the four muscles in the pectoral region that exerts a force on the upper limb. The other three muscles are the pectoralis minor, serratus anterior, and subclavius. The pectoralis major is also one of the two axial muscles that move the humerus, the other being the latissimus dorsi.
The pectoralis major can be strengthened through various pressing exercises, such as the flat barbell bench press and the flat dumbbell bench press. In these exercises, the individual lies supine on a bench with their feet flat on the ground and uses weights to extend and lower their arms slowly towards their nipple line, bringing the weights up approximately over their face at arm's length.
The pectoralis major can also be tested for length. The individual is positioned supine with their knees bent and their low back flat on the table. The examiner places the subject's arm in horizontal abduction, with the elbow extended and the shoulder in lateral rotation (palm upward). In this position, the tendon of the pectoralis major at the sternum should not be found to be unduly tense, even with maximum abduction of the arm, unless the muscle is short.
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Frequently asked questions
The pectoral region is located on the anterior chest wall and contains four muscles that exert force on the upper limb: the pectoralis major, pectoralis minor, serratus anterior, and subclavius.
The pectoral muscles are a group of skeletal muscles that connect the upper extremities to the anterior and lateral thoracic walls. They are responsible for a wide range of motions, including flexion, adduction, and internal rotation of the humerus, stabilization of the scapula, and elevating and depressing the bones of the thorax.
The pectoralis major is the largest and most superficial muscle in the pectoral region. It is thick and fan-shaped, covering the superior portion of the anterior thorax, and lies underneath the breast tissue. It has two parts: the clavicular part and the sternocostal part, which contribute to different actions.
To test the length of the pectoralis major, an examiner places the subject's arm in a position of approximately 135 degrees of abduction, with the elbow extended and the shoulder in lateral rotation (palm upward). If the muscle is of normal length, the arm should drop to table level, with the low back remaining flat on the table.
