Human Upper Limb Anatomy: Axilla, Brachial Plexus, Vasculature, Shoulder, Arm, Forearm, Wrist, and Hand

Axilla

Deep compartment of the armpit region, located inferior to the glenohumeral joint at the junction of the arm and thorax.

Apex of Axilla

Bordered by the clavicle anteriorly, scapular posteriorly, and the 1st rib; opening of the axilla for neurovascular structures.

Cervicoaxillary canal

The passageway for axillary vessels and brachial plexus components from neck to upper limb.

Base of Axilla

Bordered by skin, forming the 'armpit' we know.

Anterior axillary fold

From the lateral border of pectoralis major.

Posterior axillary fold

From latissimus dorsi and teres major plus fat.

Chest wall

Medial border from serratus anterior muscle.

Anterior wall of Axilla

Formed by clavicle, subclavius muscle, pectoralis major, and minor.

Posterior wall of Axilla

Formed by scapula, subscapularis muscle, teres major, and latissimus dorsi.

Lateral wall of Axilla

Includes intertubercular sulcus/bicipital groove, tendon of long head of biceps, and coracobrachialis tendon.

Axillary sheath

Contains axillary artery and vein, cords of the brachial plexus, and axillary lymph nodes.

Superficial fascia

Subcutaneous fatty tissue and skin, containing platysma muscle, supraclavicular nerves, and intercostal nerves.

Deep fascia

Includes musculature fascia that compartmentalizes, surrounds muscles, and attaches to bone.

Pectoral fascia

Surrounds pectoralis major and is continuous with deltoid fascia.

Suspensory ligament of axilla

Formed by the combination of axillary fascia and clavipectoral fascia.

Clavipectoral fascia

Covers pectoralis minor and subclavius, united by costocoracoid membrane, and attaches to clavicle.

Deltoid fascia

Covers the surface of the deltoid and helps compartmentalize scapular muscles.

Clavipectoral Triangle

Allows passage of neurovascular structures between axilla and pectoral region.

Axillary artery

Continuation of subclavian artery, providing blood to the shoulder, thorax, and axillary region.

Brachial artery

Continuation of the axillary artery into the arm.

Axillary vein

Formed by basilic vein and brachial veins.

Cephalic vein

Superficial continuation that joins into axillary then subclavian vein.

Basilic vein

Medial vein that joins with brachial veins to form axillary vein.

Axillary lymphatics

Consist of 5 groups, each associated with a wall of the axillary region and a vein.

Subscapular lymph nodes

Located at the posterior axillary fold, clustered near subscapular vessels.

Central lymph nodes

Located at the base, near the axillary vein.

Apical lymph nodes

Located at the apex, near the axillary vein.

Pectoral lymph nodes

Located at the anterior and medial wall, clustered near the lateral thoracic vein.

Humeral lymph nodes

Located at the lateral wall, near the axillary vein.

Breast

Bilateral glandular structures, more developed in females for nourishment of young.

Retromammary space

Space between the pectoral fascia and breast tissue.

Allows

for free movement of the breast tissue

Structure

Attaches to dermis of overlying skin via suspensory ligaments

Mammary gland lobules

converge on the nipple

Lactiferous ducts

drain into lactiferous sinuses which open at the nipple

Lactiferous sinuses

"balloons" that can pool milk expressed through 5-12 openings in the nipple

Nipple

is surrounded by pigmented areola

Breast innervation

intercostal nerves 4-6, supraclavicular nerve

Somatosensory innervation

to skin and autonomic to blood vessels and smooth muscle

Blood Supply to breast

Arterial supply: from tributaries of subclavian and axillary arteries

Medial mammary branches

via internal thoracic branch from subclavian artery

Lateral mammary branches

via lateral thoracic branch from axillary

Venous drainage

lateral mammary branches draining into the lateral thoracic vein and then into the axillary vein

Lymphatic drainage to breast

Axillary lymph nodes: 75+ % will drain here (pectoral, central, and apical groups)

Remaining nodes

Subareolar lymph nodes: near nipple and areola; Parasternal lymph nodes: drain into internal mammary nodes

Polymastia

accessory breast tissue

Polythelia

accessory nipple

Carcinoma in the breast

Causes various retraction signs: skin dimpling, nipple retraction and deviation, edema (peau d'orange skin), and abnormal bumps/contours

Invasion of retromammary space

will cause breast to elevate, a common clinical sign of breast cancer

Cancer spread

via axillary and parasternal nodes with communication to venous system forming metastasize to other areas in the body

Most common metastases

lung, liver, bone, and brain

Brachial plexus

Nervous pathway of upper limbs: carry somatosensory and somatomotor fibers as well as parasympathetics

Autonomic innervation

also picked up from middle and inferior cervical ganglia of sympathetic trunk in neck

Dorsal horn

sensory

Ventral horn

motor

Brachial plexus origin

ventral (anterior) rami of spinal nerves C5—T1

Supraclavicular region

Contains: brachial plexus, interscalene muscles, subclavian a and v, sternocleidomastoid muscle, omohyoid muscle

Infraclavicular region

Contains: axillary a and v (continuation of subclavian)

Cutaneous innervation

sensory to the skin that can be mapped onto dermatomes and regions supplied by named nerves

C4

Supplies the supraclavicular and upper shoulder region.

C5

Supplies the upper lateral arm and shoulder.

C6

Supplies the posterolateral arm and lateral forearm.

C7

Supplies the middle of forearm and hand.

C8

Supplies the posteromedial forearm and medial hand.

T1

Supplies the medial arm.

T2-T5

Supplies the axillary and pectoralis region.

Dermatomes

Sensory regions of the skin supplied by specific spinal nerves.

Myotomes

Groups of muscles that receive innervation from a single spinal nerve.

C4 Myotome

Responsible for shoulder elevation.

C5 Myotome

Responsible for shoulder abduction and elbow flexion.

C6 Myotome

Responsible for elbow flexion and wrist extension.

C7 Myotome

Responsible for elbow extension and wrist flexion.

C8 Myotome

Responsible for thumb and finger extensions.

T1 Myotome

Supplies intrinsic hand muscles.

T2-T5 Myotome

Supplies intercostal muscles.

Anterior compartment of the arm

Contains biceps and brachialis muscles.

Posterior compartment of the arm

Contains triceps muscle.

Median nerve

Innervates flexors of wrists and digits in the anterior compartment of the forearm.

Radial nerve

Innervates extensors of wrist and digits in the posterior compartment of the forearm.

Superior trunk

Formed by C5-C6, gives off nerve to subclavius and suprascapular nerve.

Middle trunk

Formed by C7.

Inferior trunk

Formed by C8-T1.

Anterior divisions

Supplies medial or lateral cord that serves the anterior compartment of the upper limb.

Posterior divisions

Supplies posterior cord that serves the posterior compartment of the upper limb.

Lateral cord

Made up of anterior divisions from middle and superior trunks.

Lateral pectoral nerve

Nerve given off by the lateral cord.

Posterior cord

Made up of posterior divisions from superior, middle and inferior trunks.

Upper subscapular nerve

Nerve given off by the posterior cord.

Thoracodorsal nerve

Nerve given off by the posterior cord.

Lower subscapular nerve

Nerve given off by the posterior cord.

Medial cord

Made up of anterior division of inferior trunk.

Medial pectoral nerve

Nerve given off by the medial cord.

Medial brachial cutaneous nerve

Nerve given off by the medial cord.

Medial antebrachial cutaneous nerve

Nerve given off by the medial cord.

Musculocutaneous nerve

Nerve from the lateral cord.

Axillary nerve

Nerve from the posterior cord.

Ulnar nerve

Nerve from the medial cord.

Supraclavicular compartment

Superior to clavicle; contains roots and trunks.

Infraclavicular compartment

Inferior to clavicle; contains divisions, cords, and branches.

C5, C6, C7

Spinal nerve contributions for the lateral cord.