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The pectoral muscles are a group of skeletal muscles that connect the front walls of the chest with the bones of the upper arm and shoulder. There are two pectoral muscles on each side of the sternum (breastbone) in the human body: the pectoralis major and the pectoralis minor. The pectoralis major is the most superficial muscle in the pectoral region and is larger and thicker than the pectoralis minor. The pectoralis minor lies beneath the pectoralis major and is responsible for drawing the shoulder forward and downward.
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What You'll Learn
Pectoralis major and minor muscles
The pectoral muscles are the group of skeletal muscles that connect the upper extremities to the anterior and lateral thoracic walls. There are two pectoral muscles on each side of the sternum (breastbone) in the human body: the pectoralis major and the pectoralis minor.
The pectoralis major is the superior-most and largest muscle of the anterior chest wall. It is a thick, fan-shaped muscle that lies underneath the breast tissue. The muscle has two heads: the clavicular and the sternocostal, which reference their area of origin. 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 upper and lower fibres of the pectoralis major insert into the crest of the greater tubercle of the humerus. The pectoralis major is active in deep or forced inspiration, assisting in breathing when the diaphragm and intercostal muscles are insufficient.
The pectoralis minor lies underneath the pectoralis major, arising from the third to fifth ribs and inserting into the coracoid process of the scapula (shoulder blade). It is much thinner and triangular in shape compared to the pectoralis major. The pectoralis minor is crucial in stabilising the scapula by drawing it downward and anteriorly against the thoracic wall.
The pectoralis major and minor muscles work together with other muscles in the pectoral region, such as the serratus anterior and subclavius, to enable a wide range of motions in the upper extremities. These include flexion, adduction, and internal rotation of the humerus, as well as elevating and depressing the bones of the thorax.
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Pectoralis muscle attachments
The pectoralis muscle is defined as any of the muscles that connect the front or ventral walls of the chest with the bones of the upper arm and shoulder. There are two pectoralis muscles on each side of the sternum (breastbone) in the human body: the pectoralis major and the pectoralis minor.
The pectoralis major is the larger and more superficial of the two, originating at the clavicle (collarbone), the sternum, the ribs, and a tendinous extension of the external oblique abdominal muscle. It extends across the upper part of the chest and is attached to a ridge at the rear of the humerus (the bone of the upper arm). The pectoralis major is also responsible for keeping the arm attached to the trunk of the body. It has two different parts that are responsible for different actions: the clavicular part and the sternocostal part. The clavicular part is close to the deltoid muscle and contributes to flexion, horizontal adduction, and inward rotation of the humerus. The sternocostal part contributes to the downward and forward movement of the arm and inward rotation when accompanied by adduction.
The pectoralis minor lies mostly beneath the pectoralis major, arising from the middle ribs and inserting into (attaching to) the scapula (shoulder blade). It aids in drawing the shoulder forward and downward.
The pectoralis major is a large, flat muscle that covers much of the chest and attaches to the humerus bone in the upper arm. It is responsible for flexing, adducting, and internally rotating the humerus, as well as contributing to the movement of the shoulder joint. The pectoralis major can be targeted from numerous training angles along the sternum and clavicle, and exercises that include horizontal adduction and elbow extensions, such as the barbell bench press, induce high activation in the sternocostal region.
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Pectoralis muscle actions
The pectoralis muscle is defined as any of the muscles that connect the front or ventral walls of the chest with the bones of the upper arm and shoulder. There are two pectoralis muscles on each side of the sternum (breastbone) in the human body: the pectoralis major and the pectoralis minor.
The pectoralis major is a prominent, fan-shaped chest muscle that acts mainly on the shoulder joint. It is the larger and more superficial of the two pectoralis muscles. The pectoralis major has three parts: the clavicular part, which originates from the anterior surface of the medial clavicle; the sternocostal part, which originates from the anterior surface of the sternum and the anterior aspects of the costal cartilages of ribs 1-6; and the abdominal part, which is the smallest and originates from the anterior layer of the rectus sheath. The main function of the pectoralis major muscle is the adduction and internal rotation of the arm in the shoulder joint. It also assists in pulling the trunk forwards or upwards when its humeral attachment is fixed, which is important in activities such as climbing.
The pectoralis minor lies underneath the pectoralis major and is the smaller and deeper of the two muscles. It originates from the middle ribs (specifically ribs 3-5) and inserts into the coracoid process of the scapula (shoulder blade). The pectoralis minor aids in drawing the shoulder forward and downward, in opposition to the trapezius muscle. It also stabilises the scapula by drawing it anteroinferiorly against the thoracic wall.
In addition to the pectoralis major and minor, the serratus anterior is another muscle that lies in the pectoral region and exerts a force on the upper limb. It is located more laterally in the chest wall and forms the medial border of the axilla region. The serratus anterior has several strips that originate from the lateral aspects of ribs 1-8 and attach to the costal (rib-facing) surface of the medial border of the scapula. One of its functions is to rotate the scapula, allowing the arm to be raised over 90 degrees. It also protracts the scapula, holding it against the ribcage.
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Pectoralis muscle innervation
The pectoralis muscle is defined as any of the muscles that connect the front or ventral walls of the chest with the bones of the upper arm and shoulder. There are two pectoralis muscles on each side of the sternum (breastbone) in the human body: the pectoralis major and the pectoralis minor.
The pectoralis major is the larger and more superficial of the two muscles, originating at the clavicle (collarbone), the sternum, the ribs, and a tendinous extension of the external oblique abdominal muscle. It extends across the upper part of the chest and is attached to a ridge at the rear of the upper arm bone (humerus). The pectoralis major is often referred to as the "pecs" muscle, especially in gym and fitness contexts.
The pectoralis major has three distinct 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 clavicular part helps to flex the extended arm up to 90 degrees, while the sternocostal part pulls the arm downwards. The pectoralis major as a whole is responsible for adduction and internal rotation of the arm in the shoulder joint.
The pectoralis major receives dual motor innervation by the medial pectoral nerve and the lateral pectoral nerve, also known as the lateral anterior thoracic nerve. The medial pectoral nerve provides innervation to the sternal head, which receives sensory input from the C7, C8, and T1 nerve roots via the lower trunk of the brachial plexus. The clavicular head, on the other hand, is innervated by the C5 and C6 nerve roots through the upper trunk and lateral cord of the brachial plexus, which gives off the lateral pectoral nerve.
The pectoralis minor lies beneath the pectoralis major and connects the middle ribs to the scapula (shoulder blade). It aids in drawing the shoulder forward and downward, working in opposition to the trapezius muscle.
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Pectoralis muscle anatomy
The pectoral region is located on the anterior chest wall and contains four muscles: the pectoralis major, pectoralis minor, serratus anterior, and subclavius. The pectoralis major is the largest and most superficial muscle in the pectoral region. It is thick and fan-shaped, lying underneath the breast tissue and forming the anterior wall of the axilla. The pectoralis major consists of two heads: the clavicular and the sternocostal, which reference their area of origin. 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 to seven costal cartilages, and the aponeurosis of the external oblique abdominal muscle. The sternocostal head is larger than the clavicular head. The upper and lower fibres of the pectoralis major insert into the crest of the greater tubercle of the humerus. The pectoralis major is involved in deep or forced inspiration and can assist in breathing along with other muscles when the diaphragm and intercostal muscles are insufficient.
The pectoralis minor lies underneath the pectoralis major, arising from the middle (third to fifth) ribs and inserting into the scapula (shoulder blade). It aids in drawing the shoulder forward and downward. The serratus anterior is located laterally in the chest wall and forms the medial border of the axilla region. It consists of several strips that originate from the lateral aspects of ribs one to eight and attach to the costal surface of the medial border of the scapula. The serratus anterior rotates the scapula, allowing the arm to be raised over 90 degrees. The subclavius is a small muscle located directly underneath the clavicle, running horizontally. It provides minor protection to the underlying neurovascular structures and anchors and depresses the clavicle.
The pectoralis major is involved in adduction or depression of the arm and its rotation forward about the axis of the body. It also assists the latissimus dorsi and teres major muscles in pulling the trunk up when the arms are raised and fixed, such as in mountain climbing. The pectoralis major tendon rupture is a rare shoulder injury that is becoming more common due to the increased emphasis on healthy lifestyles. It is seen in activities that involve the arm being in extension and external rotation, such as weight lifting.
The pectoralis major shows variation in muscle fibre length, differing from most muscle fibres in the human body, which typically have a uniform length. This variation in the pectoralis major potentially allows for more power production through differing muscle shortening velocities. The muscle is highly vascularised through the thoracoacromial artery, making it useful for flap repairs in neck surgery and soft tissue reconstruction of the neck and face following trauma or tumour-related operations.
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Frequently asked questions
Pectoral muscles are the group of skeletal muscles that connect the upper extremities to the anterior and lateral thoracic walls. There are two such muscles on each side of the sternum (breastbone) in the human body: pectoralis major and pectoralis minor.
The pectoralis major is the most superficial muscle in the pectoral region. Its functions include adduction and internal rotation of the humerus, flexion of the upper limb, and depressing and abducting the scapula.
The pectoralis minor is crucial in stabilizing the scapula by pulling it downward and anteriorly against the thoracic wall. It also aids in drawing the shoulder forward and downward.
