Axillary SoftChalk Notes
Axilla-region between arm and thorax in which all nerves and vessels pass into the upper limb.
-Boundaries
1. Apex of Axilla: cervico-axillary canal, formed by the clavicle, scapula, and the
first rib.
2. Base of Axilla: axillary fossa (armpit), formed by fascia and skin.
3. Anterior: formed by the pectoralis major and minor.
4. Posterior: formed by the subscapularis, lastissimus dorsi, and teres major.
5. Medial boundary of the axilla: formed by the ribs, intercostal muscles, and
serratus anterior.
6. Lateral: formed by the intertubercular groove of the humerus.
-Contents
1. Axillary Vessels
> Enclosed in Axillary Sheath (prevertebral fascia): fascia covering axilla
> Axillary artery (continuation of subclavian artery)
> Axillary vein (continuation of the subclavian vein)
2. Axillary lymph nodes: 20-30 deep nodes arranged in 5 main groups: pectoral,
subscapular, humeral, central and apical.
3. Brachial Plexus: provides motor, sensory, and sympathetic innervation to the upper
limb.
-Axillary Artery:
> Represents the continuation of the subclavian artery on each side of the body.
> The transitions between subclavian and axillary arteries befins at the lateral edge of first rib.
> The axillary artery becomes the brachial artery as it passes the lower border of teres major.
> Central structure of the axilla.
> The cords of the brachial plexus are named by their position relative to the second segment of
the axillary artery. Thus, Lateral Cord, Medial Chord, and Posterior Cord.
- Axillary Artery:
> The axillary artery is divided into three segments, defined by the position of the pectoralis
minor.
o
1st segment
- Located proximal to the pectoralis minor
- Single branch: Superior Thoracic Artery
> Lies inferior to subclavius, supplies muscles in the 1st 2 intercostal
spaces, and Anastomoses with intercostal and/or internal thoracic
arteries.
o
2nd segment
- Located deep to pectoralis minor.
- Two branches:
1. Thoracoacromial artery: short wide trunk that divides into 4
branches, including acromial, deltoid, pectoral, and clavicular
2. Lateral thoracic artery: Supplies serratus anterior and lateral aspect of
the breast.
o
3rd segment
- Located distal to pectoralis minor
- Three branches:
1. Subscapular artery: contributes to an arterial anastomoses around
the scapula(circumflex scapular artery) and forms the
thoracododorsal artery which supplies latissimus dorsi.
2. Anterior humeral circumflex: smaller of the 2 humeral circumflex
arteries, which form an arterial anastomoses around the
surgical neck of the humerus.
3. Posterior humeral circumflex: larger of the two, passes through the
quadrangle space with the axillary nerve.
***Clinical Correlate: Compression of the axillary artery may be necessary when
profuse bleeding occurs. The distal segment can be palpated in
the inferior lateral wall of the axilla. It may also be compressed
at its origin, with pressure in the angle between
sternocleidomastoid and the clavicle.
Axillary Vein:
> situated superficial to the axillary artery throughout its course through the axillary fossa.
> formed by the union of the brachial and basilic veins.
> proximally, the axillary vein becomes the subclavian as it crosses the first rib.
***Clinical Correlate: Wounds in the axilla often involve the axillary vein due to its exposed
position and are particularly dangerous because of profuse bleeding and the risk of air
emboli (bubbles) entering the blood.
Axillary Lymph Nodes: arranged into 5 groups Pectoral, Subscapular, Humeral, Central, and Apical
1.
2.
3.
4.
5.
Humeral (lateral) nodes lie along the lateral wall of the axilla, medial and posterior to the
axillary vein. They drain most of upper limb, except that which is carried by
lymphatics traveling with the cephalic vein (which drain to apical or
infraclavicular nodes).
Pectoral (anterior) nodes lie along the medial wall of the axilla, around the lateral thoracic
vein. They drain the anterior chest wall and breast (upper outer quadrant)
Subscapular (posterior) nodes lie along the subscapular vessels and drain upper back &
shoulder.
Central nodes are located deep to pectoralis minor near the base of the axilla and receive
lymph from humeral, pectoral, & subscapular nodes.
Apical nodes are located at the apex of the axilla and receive lymph from central nodes and
lymph following cephalic vein.
 Efferent lymphatic vessels either drain to supraclavicular nodes or they unite to form the
subclavian trunk which drain into either the right lymphatic duct of the thoracic duct on the left.
These ducts empty lymph into the venous system at the venous angle (junction of internal
jugular vein and subclavian vein).
***Clinical Correlates
1. Lymphangits is an inflammation of the lymphatic channels that occurs as a result of
infection at a site distal to the channel.
2. Lymphadema is swelling as a result of accumulated lymph in the subcutaneous tissue,
due to drainage impediment after removal of axillary lymph nodes.
3. Staging and determining the appropriate treatment of breast cancer, excision and
pathological analysis of axillary lymph nodes is often necessary. Because axillary
lymph nodes are arranged and receive lymph (and cancer cells) in a specific
order, removing and excising lymph nodes in that order is important in
determing how far the cancer has metastasized.
Brachial Plexus
> Network of nerves supplying somatic sensory, somatic motor, and sympathetic innervation to
the upper extremity. It is formed by the union of ventral primary rami of C5-T1.
> These ventral rami lie between the anterior and middle scalene muscles and are termed roots
(branches: dorsal scapular & long thoracic nerves).
>As the ventral rami pass into the posterior triangle of the neck, they form trunks.
- Roots C5-C6 join to form the Superior/Upper Trunk (branch=suprascapular n and nerve to
subclavian)
- Root C7 forms the Middle Trunk
- Roots C8 and T1 unite to form the Inferior/Lower Trunk
>Trunks divide into Anterior and Posterior Divisions posterior to the clavicle.
Divisions unit to form Cords.
- Anterior divisons of Superior and Middle Trunks form the Lateral Cord.
- Anterior divisions of the Inferior Trunk form the Medial Cord.
- Posterior Divisions of all trunks form the Posterior Cord.
> Each cord divides of the brachial plexus has several branches.
- Lateral Cord:
1. Lateral Pectoral Nerve- Innervates Pectoralis Major
2. Musculocutaneous Nerve- Innervates flexors (anterior compartment) of the
arm, changes name in the forearm to Lateral Antebrachial Cutaneous
Nerve (sensory-skin of forearm)
3. Median Nerve (Lateral Root)- Unites with Medial Root to form Median Nerve
Proper, which innervates forearm flexors/some intrinsic muscles of the
hand (thenar, thumb musculature)
- Medial Cord:
1. Medial Pectoral Nerve- Innervates Pectoralis Major and Minor
2. Medial Brachial Cutaneous Nerve- Sensory to medial arm
3. Medial Antebrachial Cutaneous Nerve- sensory to medial forearm
4. Ulnar Nerve-Innervates most muscles of hand, as well as carpi ulnaris and the
ulnar part of flexor digitorum profundus in forearm.
5. Median Nerve(Medial Root)- Unites with Lateral Root to form Median Nerve
Proper, which innervates forearm flexors/some intrinsic muscles of the
hand (thenar, thumb, side of palm)
- Posterior Cord:
1. Upper and Lower Subscapular Nerves: Innervates subscapularis & teres major
2. Thoracodorsal Nerve: Innervates latissimus dorsi
3. Axillary Nerve: Innervates deltoid and teres minor, and skin over the shoulder
4. Radial Nerve: Innervates extensors of the elbow, wrist, and digits and the skin
over the posterior arm, forearm and part of the dorsum of the hand.