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The armpit, also known as the axilla, is an area of the body that lies underneath the glenohumeral joint, at the junction of the upper limb and the thorax. The axilla contains several muscles, including the pectoralis major, pectoralis minor, subscapularis, teres major, latissimus dorsi, and serratus anterior. These muscles are important for the function of the shoulders and arms, and their improper use can lead to overuse of the neck and front of the shoulders, resulting in tension and potential injuries. The axilla also serves as a passageway for neurovascular and muscular structures to enter and exit the upper limb.
| Characteristics | Values |
|---|---|
| Area | Directly under the shoulder joint |
| Location | Between the arm and the thoracic cage |
| Boundaries | Serratus anterior muscle, thoracolumbar fascia, pectoral muscles, subscapularis, teres major, latissimus dorsi muscle |
| Contains | Axillary vein, axillary artery, brachial plexus, lymph nodes, fat |
| Muscle tendons | Biceps brachii, coracobrachialis |
| Muscle groups | Pectoralis major, pectoralis minor, serratus anterior, latissimus dorsi, trapezius |
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What You'll Learn
The pectoralis major and minor muscles
The pectoralis minor is a superficial muscle on the anterior aspect of the chest or thoracic wall, located deep only to the pectoralis major. It arises as three separate heads from the anterior surface of the 3rd, 4th, and 5th ribs near the corresponding costal cartilages and extends superolaterally to form a flat tendon. The pectoralis minor lies underneath its larger counterpart muscle, the pectoralis major. Together, these muscles form part of the anterior wall of the axilla region.
The pectoralis major is a powerful muscle that aids in rotating the arm inward and moving it closer to the body. It moves each shoulder joint in four distinct directions and keeps the arms attached to the body. It is also involved in climbing, as it pulls the trunk forwards or upwards when its humeral attachment is fixed. The pectoralis major is commonly developed through bench press exercises and can be torn as a result of trauma or injury during weight training or contact sports. Tears in the pectoralis major muscle can be repaired through surgical methods, where the torn tendon is released from adhesions and reattached to the humerus using anchors and strong sutures.
The pectoralis minor is important clinically and as a surgical landmark due to the structures that lie below or deep to the muscle and its tendon. It is used as a reference point for the three divisions of the axillary artery and the nerves and blood supply to the upper limb run deep to the muscle. The pectoralis minor also produces various movements of the scapula and can be used as an accessory muscle of respiration.
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Serratus anterior muscle
The serratus anterior is a fan-shaped muscle that originates on the superolateral surfaces of the first to eighth or ninth ribs at the lateral wall of the thorax. Its fibres run obliquely and it wraps around the ribcage, passing beneath the scapula to insert on the underside of the scapula on its medial border. The lowest four digitations of the serratus anterior interdigitate with the fibres of the external oblique.
The serratus anterior is also known as the "big swing muscle" or "'boxer's muscle' as it is responsible for the protraction of the scapula, or the pulling of the scapula forward and around the rib cage. It acts in concert with the upper and lower fibres of the trapezius muscle to sustain upward rotation of the scapula, which allows for overhead lifting. The serratus anterior is a key scapular stabiliser, keeping the shoulder blades against the rib cage when at rest and during movement.
The serratus anterior is innervated by the long thoracic nerve, a branch of the brachial plexus. The vascular supply to the serratus anterior comes from the superior and lateral thoracic arteries (branches of the axillary artery) as well as branches from the thoracodorsal artery (branch of the subscapular artery).
Weakness of the serratus anterior can lead to altered line of pull of the rotator cuff muscle, which could increase the risk of subacromial impingement syndrome. It can also cause scapula winging, where the scapula tilts in a "wing-like" manner.
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Teres major and latissimus dorsi muscle
The axilla, or armpit, is the area directly under the shoulder joint. The axilla includes the axillary space, an anatomical space within the shoulder girdle between the arm and the thoracic cage. The axilla is bounded by several muscles, including the serratus anterior muscle, thoracolumbar fascia, pectoralis muscles, subscapularis, teres major, and latissimus dorsi muscle.
The latissimus dorsi is a large, powerful muscle on the back of the torso. The teres major is a small muscle that assists the latissimus in some of its actions. The latissimus dorsi covers much of the back, while the teres major is found just superior to the latissimus, where it connects from the torso to the humerus.
The latissimus dorsi has a broad area of attachment. It attaches to the spinous processes of vertebrae T7-T12 and then, via the thoracolumbar aponeurosis, connects to all of the lumbar vertebrae, the sacrum, and the posterior third of the iliac crest. The latissimus dorsi can also attach to ribs 9-12 and the inferior angle of the scapula. As the muscle fibers extend toward the axilla, they wind around the anterior aspect of the teres major muscle to insert as a flat tendon on the floor of the intertubercular (bicipital) groove of the humerus.
The primary actions of both the latissimus dorsi and teres major are the medial rotation of the humerus when the arm is abducted. The latissimus dorsi is also important for maintaining balanced movement and stability of the shoulder complex. It is an essential part of the back, and training the latissimus dorsi can provide benefits for everyday movement and life. For example, the latissimus dorsi can raise the trunk upward when the arms are fixed above the head, as in climbing or performing a chin-up. It is also important for swimming and rowing.
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Axillary lymph nodes
The axilla, or armpit, is a small space in the body located between the upper thoracic wall and the arm. The axilla contains the axillary lymph nodes, which are a grouping of 20 to 40 lymph nodes. Lymph nodes are small, bean-shaped organs composed of lymphatic tissue. They are part of the lymphatic system, which helps fight infections and is made up of lymph vessels, lymph fluid, lymph nodes, bone marrow, and lymphatic organs.
The axillary lymph nodes act as a checkpoint for lymph draining from the arms, breast, and chest wall. Lymph is a watery, colourless fluid that sweeps up cancer cells and removes them from the body. The axillary lymph nodes are of particular clinical significance as they are often the first site of breast cancer metastasis. In fact, the most common type of cancer that spreads to the axillary lymph nodes is breast cancer. Other cancers that may spread to these nodes include skin cancers, such as melanoma and non-melanoma.
Axillary lymphadenopathy, or swelling of the axillary lymph nodes, is usually due to infectious conditions like sarcoidosis, cat-scratch disease, and Staphylococcal and Streptococcal skin infections. It can also be caused by malignancies such as breast cancer, leukaemia, and lymphoma. In the early stages of cancer, it is usually not possible to feel the cancer in the axillary lymph nodes. However, in more advanced stages, a lump may be felt in the armpit as the nodes become enlarged.
If cancer is suspected to have spread to the axillary lymph nodes, a surgical procedure called axillary lymph node dissection (ALND) may be performed. During this procedure, an incision is made in the armpit, and lymph nodes are removed for examination. This surgery is typically done to determine the extent of cancerous spread and is often performed as part of breast cancer surgery.
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Axillary artery and vein
The axilla, or armpit, is the area on the human body directly under the shoulder joint. The axillary vein is a large blood vessel that conveys blood from the lateral aspect of the thorax, axilla (armpit), and upper limb toward the heart. There is one axillary vein on each side of the body. The axillary vein is formed by the confluence of the brachial and basilic veins. At its terminal part, it is joined by the cephalic vein. The axillary vein receives tributaries that correspond to the branches of the axillary artery, including the subscapular, circumflex humeral, lateral thoracic, and thoraco-acromial veins.
The axillary artery is a major blood vessel that supplies blood to the arm and hand. It is a continuation of the subclavian artery and begins at the outer border of the first rib, running laterally across the axilla. The axillary artery has several smaller branches, including the posterior and anterior circumflex arteries, which often have a common trunk. An arterial branch is named for its course, not its origin. The axillary artery can be safely clamped without endangering the arm, but only in a location proximal to the origin of the subscapular artery. The right axillary artery is often used as an arterial cannulation site in cardiac surgery, particularly for the repair of aortic dissection and replacement of the ascending aorta and aortic arch.
The axillary vein and artery travel in a bundle with several neurovascular structures of the axilla, including the lateral and medial pectoral nerves, the medial cord of the brachial plexus, the ulnar nerve, and the medial cutaneous nerve of the arm. The axillary vein accompanies the axillary artery along its course through the armpit region, running on the anteromedial side of the artery and partially overlapping it.
The underarm is important for the function of the shoulders and arms. The serratus anterior muscle and the lats (latissimus dorsi) are located in the underarm/back area. If these muscles are not used properly, the muscles in the neck and shoulders may be overused, leading to neck tension and contributing to shoulder injuries.
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Frequently asked questions
The axilla, or armpit, contains several muscles, including the pectoralis major, pectoralis minor, subscapularis, teres major, and latissimus dorsi.
Your armpit muscles are important for the function of your shoulders and arms. Without proper utilisation of these muscles, you may overuse the muscles in your neck and the front of your shoulders, leading to severe neck tension and potentially contributing to shoulder injuries.
Pain, itchiness, and referred pain in the head, neck, and shoulder can indicate fascial restrictions or muscle tears in the armpit area. If you suspect an injury, it is recommended to consult a doctor or a qualified healthcare professional.
