KAAP 620: Upper Extremity, Back, Shoulder, Chest, and Arm Anatomy

Comprehensive review flashcards covering the axilla, brachial plexus, arterial supply, venous drainage, back and posterior shoulder muscles, chest, arm compartments, and intermuscular spaces.

Axilla

An anatomical pyramid-shaped space whose anterior wall is formed by the pectoralis major and minor, medial wall by the serratus anterior and 4th rib, lateral wall by the intertubercular sulcus of the humerus, and posterior wall by the subscapularis, teres major, and latissimus dorsi.

Cervico-Axillary Canal

The apex and passageway into the axilla bounded anteriorly by the clavicle, medially by the 1st rib, and posterolaterally by the superior border of the scapula.

Cephalic Vein

A major superficial vein of the lateral upper limb that ascends along the deltopectoral groove, enters the clavipectoral (deltopectoral) triangle, and pierces fascia to drain directly into the axillary vein.

Basilic Vein

A major superficial vein of the medial forearm and arm that pierces the deep fascia of the arm to join the venae comitantes of the brachial artery and form the axillary vein.

Median Cubital Vein

A superficial communicating vein located in the cubital fossa that shunts blood obliquely from the cephalic vein to the basilic vein.

Median Antebrachial Vein

A highly variable superficial vein ('the wild child') ascending up the midline of the anterior forearm, draining into the median cubital, cephalic, or basilic vein.

Axillary Artery

The arterial continuation of the subclavian artery that begins at the lateral border of the 1st rib, transitions into the brachial artery at the inferior border of the teres major muscle, and is divided into three parts by the pectoralis minor muscle.

Axillary Artery: First Division

The part of the axillary artery located proximal to the pectoralis minor muscle; it yields a single branch: the superior thoracic artery.

Axillary Artery: Second Division

The part of the axillary artery located posterior to the pectoralis minor muscle; it gives off two branches: the thoracoacromial artery and the lateral thoracic artery.

Axillary Artery: Third Division

The part of the axillary artery located distal to the lateral border of the pectoralis minor muscle; it gives off three branches: the subscapular artery, the anterior circumflex humeral artery, and the posterior circumflex humeral artery.

Thoracoacromial Artery

A branch of the second part of the axillary artery that curls around the upper border of the pectoralis minor and pierces the clavipectoral fascia to divide into four branches: pectoral, clavicular, acromial, and deltoid.

Subscapular Artery

The largest branch of the third division of the axillary artery; it descends along the subscapularis muscle and branches into the circumflex scapular artery and the thoracodorsal artery.

Thyrocervical Trunk

A major branch of the first part of the subclavian artery that typically branches into the inferior thyroid artery, suprascapular artery, and transverse cervical artery (cervicodorsal trunk).

Profunda Brachii Artery

Also called the deep brachial artery; the largest branch of the brachial artery, which enters the triangular interval alongside the radial nerve and terminates into radial and middle collateral branches.

Brachial Plexus: Roots

The five anterior (ventral) rami of spinal nerves $C5$, $C6$, $C7$, $C8$, and $T1$ that pass through the interscalene triangle between the anterior scalene and middle scalene muscles.

Brachial Plexus: Trunks

The three primary trunks formed in the neck: the Superior trunk (formed by $C5$ and $C6$ roots), the Middle trunk (continuation of the $C7$ root), and the Inferior trunk (formed by $C8$ and $T1$ roots).

Brachial Plexus: Divisions

The functional splits of the trunks located posterior to the clavicle: three anterior divisions supplying the flexor compartments and three posterior divisions supplying the extensor compartments of the upper limb.

Brachial Plexus: Cords

The three structural groupings named relative to the axillary artery: the Lateral cord (anterior divisions of superior and middle trunks), Medial cord (anterior division of inferior trunk), and Posterior cord (posterior divisions of all three trunks).

Brachial Plexus Peripheral Nerves Mnemonic

'3 Musketeers Assassinate 5 Rats, 5 Mice, And 2 Unicorns', identifying: Musculocutaneous n. ($C5\text{--}C7$; thumb, index, middle), Axillary n. ($C5\text{--}C6$; thumb, index), Radial n. ($C5\text{--}T1$; all 5 fingers), Median n. ($C5\text{--}T1$; all 5 fingers), and Ulnar n. ($C8\text{--}T1$; ring, pinky).

Trapezius Muscle

Extrinsic superficial back muscle; Origin: Superior nuchal line, external occipital protuberance, ligamentum nuchae, spinous processes of $C7\text{--}T12$; Insertion: Lateral 1/3 of clavicle, acromion, spine of scapula; Action: Upper fibers elevate scapula, middle fibers adduct (retract) scapula, lower fibers depress scapula; Innervation: Spinal accessory nerve (CN XI).

Latissimus Dorsi Muscle

Extrinsic superficial back muscle; Origin: Spinous processes of $T8\text{--}L5$, sacrum, iliac crest, and ribs 10–12; Insertion: Floor of the intertubercular sulcus of the humerus; Action: Humeral adduction, extension, and internal rotation; Innervation: Thoracodorsal nerve ($C6\text{--}C8$).

Levator Scapulae Muscle

Extrinsic superficial back muscle; Origin: Posterior tubercles of transverse processes of $C1\text{--}C4$; Insertion: Superior medial vertebral border of scapula to the root of the scapular spine; Action: Elevates the scapula; Innervation: Dorsal scapular nerve ($C4\text{--}C5$).

Rhomboid Major and Minor Muscles

Extrinsic superficial back muscles; Origin: Minor from spinous processes of $C7\text{--}T1$, Major from spinous processes of $T2\text{--}T5$; Insertion: Medial border of the scapula; Action: Scapular retraction and elevation; Innervation: Dorsal scapular nerve ($C4\text{--}C5$).

Triangle of Auscultation

A triangular clinical space bounded by the superior horizontal border of the latissimus dorsi, the inferolateral border of the trapezius, and the medial border of the scapula (or rhomboideus major), which facilitates stethoscopic auscultation of respiratory sounds due to thinning of the musculature.

Serratus Posterior Muscles

Extrinsic intermediate back muscles innervated by intercostal nerves; the Serratus Posterior Superior originates from the nuchal ligament and $C7\text{--}T3$ spinous processes inserting on ribs 2–4; the Serratus Posterior Inferior originates from $T11\text{--}L2$ spinous processes inserting on ribs 8–12.

Splenius Capitis Muscle

Intrinsic superficial back muscle; Origin: Lower 1/2 of ligamentum nuchae and spinous processes of $C7\text{--}T4$; Insertion: Mastoid process and lateral 1/3 of superior nuchal line; Action: Bilaterally extends head/neck; unilaterally produces ipsilateral rotation and lateral flexion; Innervation: Posterior (dorsal) rami of middle cervical nerves.

Splenius Cervicis Muscle

Intrinsic superficial back muscle; Origin: Spinous processes of $T3\text{--}T6$; Insertion: Transverse processes of $C1\text{--}C3$; Action: Bilaterally extends neck; unilaterally produces ipsilateral rotation and lateral flexion; Innervation: Posterior (dorsal) rami of middle cervical nerves.

Erector Spinae Muscle Group

Intrinsic intermediate back muscles sharing a broad common origin tendon and innervated by posterior (dorsal) rami; arranged laterally to medially as Iliocostalis (lumborum, thoracis, cervicis), Longissimus (thoracis, cervicis, capitis), and Spinalis (thoracis, cervicis, capitis); bilaterally extend the vertebral column and unilaterally produce lateral flexion.

Semispinalis Muscle

Part of the transversospinal intrinsic deep muscle group; Origin: Transverse processes of $C4\text{--}T12$; Insertion: Spinous processes of superior vertebrae spanning 4 to 6 segments (capitis attaches to occipital bone); Action: Bilaterally extends vertebral column/head; unilaterally produces contralateral rotation; Innervation: Posterior (dorsal) rami.

Multifidus Muscle

Part of the transversospinal intrinsic deep muscle group; Origin: Sacrum, PSIS, mammillary processes of lumbar vertebrae, transverse processes of $T1\text{--}T3$, articular processes of $C4\text{--}C7$; Insertion: Spinous processes spanning 2 to 4 segments superiorly; Action: Stabilizes vertebrae during local movements; Innervation: Posterior (dorsal) rami.

Rotatores Muscle

Deepest transversospinal intrinsic back muscles (brevis and longus); Origin: Transverse processes of vertebrae; Insertion: Junction of lamina and transverse process of vertebrae 1 to 2 segments above origin; Action: Stabilizes vertebrae, assists extension and rotation; Innervation: Posterior (dorsal) rami.

Levatores Costarum Muscles

Minor intrinsic deep back muscles; Origin: Tips of transverse processes of $C7$ and $T1\text{--}T11$; Insertion: Pass inferolaterally to insert on ribs between tubercle and angle; Action: Elevate ribs to assist inspiration and assist lateral flexion; Innervation: Posterior rami of $C8\text{--}T11$ spinal nerves.

Deltoid Muscle

Shoulder muscle; Origin: Lateral 1/3 of clavicle, acromion, and spine of scapula; Insertion: Deltoid tuberosity of humerus; Action: Anterior part flexes and internally rotates, middle part abducts, posterior part extends and externally rotates the humerus; Innervation: Axillary nerve ($C5\text{--}C6$).

Supraspinatus Muscle

Rotator cuff muscle; Origin: Supraspinous fossa of scapula; Insertion: Superior facet of greater tubercle of humerus; Action: Initiates shoulder abduction; Innervation: Suprascapular nerve ($C5\text{--}C6$).

Infraspinatus Muscle

Rotator cuff muscle; Origin: Infraspinous fossa of scapula; Insertion: Middle facet of greater tubercle of humerus; Action: Shoulder external rotation; Innervation: Suprascapular nerve ($C5\text{--}C6$).

Teres Minor Muscle

Rotator cuff muscle; Origin: Middle part of the lateral border of the scapula; Insertion: Inferior facet of greater tubercle of humerus; Action: Shoulder external rotation; Innervation: Axillary nerve ($C5\text{--}C6$).

Subscapularis Muscle

Rotator cuff muscle; Origin: Subscapular fossa of scapula; Insertion: Lesser tubercle of humerus; Action: Shoulder internal rotation; Innervation: Upper and lower subscapular nerves ($C5\text{--}C6$).

Teres Major Muscle

Posterior shoulder muscle; Origin: Inferior part of the lateral border of the scapula; Insertion: Medial lip of the intertubercular sulcus of the humerus; Action: Shoulder adduction, internal rotation, and weak extension; Innervation: Lower subscapular nerve ($C6$).

Serratus Anterior Muscle

Thoracic wall muscle; Origin: External surface of lateral ribs 1–8; Insertion: Anterior surface of the medial border of the scapula; Action: Scapular protraction and stabilization against the thoracic cage; Innervation: Long thoracic nerve ($C5\text{--}C7$).

Pectoralis Major Muscle

Anterior chest muscle; Origin: Anterior medial clavicle, sternum, and superior 6 costal cartilages; Insertion: Lateral lip of the intertubercular sulcus of the humerus; Action: Shoulder adduction, internal rotation, and flexion; Innervation: Medial and lateral pectoral nerves.

Pectoralis Minor Muscle

Deep anterior chest muscle; Origin: Ribs 3–5 near their costal cartilages; Insertion: Coracoid process of the scapula; Action: Scapular protraction and depression/stabilization; Innervation: Medial pectoral nerve ($C8\text{--}T1$).

Subclavius Muscle

Anterior thoracic muscle; Origin: Junction of 1st rib and costal cartilage; Insertion: Inferior surface of middle 1/3 of the clavicle; Action: Depresses and stabilizes the clavicle; Innervation: Nerve to subclavius (subclavian nerve, $C5\text{--}C6$).

Coracobrachialis Muscle

Anterior compartment arm muscle; Origin: Coracoid process of scapula; Insertion: Proximal 1/3 of medial humeral shaft; Action: Shoulder flexion and adduction; Innervation: Musculocutaneous nerve ($C5\text{--}C7$).

Biceps Brachii Muscle

Two-headed anterior arm muscle; Origin: Long head from the supraglenoid tubercle, Short head from the coracoid process; Insertion: Radial tuberosity and bicipital aponeurosis; Action: Forearm supination, elbow flexion (most potent in supination), and weak shoulder flexion; Innervation: Musculocutaneous nerve ($C5\text{--}C7$).

Brachialis Muscle

Deep anterior arm muscle; Origin: Distal 1/2 of the anterior humeral shaft; Insertion: Coronoid process and tuberosity of the ulna; Action: Major elbow flexor in all forearm positions (including pronation); Innervation: Musculocutaneous nerve ($C5\text{--}C7$).

Brachioradialis Muscle

Superficial forearm muscle; Origin: Lateral supracondylar ridge of humerus; Insertion: Radial styloid process; Action: Elbow flexion when the forearm is in the mid-pronated (neutral) position; Innervation: Radial nerve ($C5\text{--}T1$).

Triceps Brachii Muscle

Three-headed posterior arm muscle; Origin: Long head from infraglenoid tubercle, Lateral head from posterior humerus superior to radial groove, Medial head from posterior humerus inferior to radial groove; Insertion: Olecranon process of ulna; Action: Primary elbow extensor; Innervation: Radial nerve ($C6\text{--}C8$).

Anconeus Muscle

Posterior elbow muscle; Origin: Lateral epicondyle of humerus; Insertion: Olecranon process and superior posterior surface of the ulna; Action: Assists triceps in terminal elbow extension and stabilizes the elbow joint; Innervation: Radial nerve.

Quadrangular Space

Intermuscular space bounded superiorly by teres minor, inferiorly by teres major, medially by the long head of the triceps brachii, and laterally by the surgical neck of the humerus; contains the axillary nerve and posterior humeral circumflex artery.

Triangular Space

Intermuscular space bounded superiorly by teres minor, inferiorly by teres major, and laterally by the long head of the triceps brachii; transmits the circumflex scapular artery.

Triangular Interval

Intermuscular space bounded superiorly by teres major, medially by the long head of the triceps brachii, and laterally by the lateral head of the triceps brachii (or humerus); transmits the radial nerve and profunda brachii (deep brachial) artery.

Deltopectoral Groove

The surface indentation along the border between the anterior deltoid and clavicular head of pectoralis major which transmits the cephalic vein and the deltoid branch of the thoracoacromial artery.