Anatomy of the Shoulder Girdle and Upper Limb: Brachial Plexus, Bones, Joints, Vessels, and Muscles

Brachial Plexus Anatomy

Roots, Trunks, Divisions, and Cords

The brachial plexus is a network of nerves that supplies the muscles and skin of the shoulder, arm, and hand. It is formed by the anterior rami of spinal nerves C5, C6, C7, C8, and T1.

• Roots: Five roots (C5, C6, C7, C8, T1) form the basis of the plexus.

• Trunks: Roots combine to form three trunks:

  • Superior trunk: C5 and C6

  • Middle trunk: C7

  • Inferior trunk: C8 and T1

• Divisions: Each trunk splits into anterior and posterior divisions.

• Cords: Divisions regroup to form three cords:

  • Lateral cord: from anterior divisions of superior and middle trunks

  • Posterior cord: from all posterior divisions

  • Medial cord: from anterior division of inferior trunk

Terminal branches of the brachial plexus include the musculocutaneous, median, ulnar, radial, and axillary nerves. These nerves innervate muscles and skin of the upper limb.

Major Arteries and Veins of the Upper Limb

Arterial Supply

The upper limb receives blood from several major arteries, which branch from the aorta and subclavian arteries.

• Brachiocephalic artery: branches from the aorta

• Subclavian artery: continuation of the brachiocephalic

• Axillary artery: becomes the main artery at the first rib in the axilla

• Brachial artery: begins at the lower border of the teres major muscle

Venous Drainage

• Brachiocephalic vein: formed from the subclavian vein and internal jugular vein

• Subclavian vein: at the outer rib of the first rib

• Axillary vein: in the axilla area

• Brachial vein: deep vein that runs along the brachial artery

• Basilar vein: superficial vein running up the medial side of the arm and forearm

• Cephalic vein: superficial vein running along the lateral side of the arm and forearm

Shoulder Girdle Bones

Clavicle Anatomy

The clavicle (collarbone) is a long bone that serves as a strut between the shoulder blade and the sternum. It has a superior and inferior view, with key features including:

• Tubercle

• Trapezoid line

• Acromial facet

Scapula Anatomy

The scapula (shoulder blade) is a flat, triangular bone with several important bony landmarks:

• Spine

• Acromion

• Glenoid cavity

• Coracoid process

• Supraspinous fossa

• Infraspinous fossa

• Subscapular fossa

• Superior angle

• Inferior angle

• Medial border

• Lateral border

• Superior border

• Supraglenoid tubercle

• Infraglenoid tubercle

Humerus Anatomy

The humerus is the long bone of the upper arm. It articulates with the scapula at the glenoid cavity and has several prominent features:

• Head: ball-shaped, articulates with the glenoid cavity

• Deltoid tuberosity: lateral side

• Radial groove: posterior surface

• Capitulum and trochlea: distal end, articulate with radius and ulna

• Medial and lateral epicondyles: distal projections for muscle attachment

Joints of the Shoulder Girdle

Classification and Structure

The shoulder girdle contains several important joints:

• Sternoclavicular (SC) joint: synovial articulation between the sternum and clavicle

• Acromioclavicular (AC) joint: synovial joint between the acromion of the scapula and the clavicle

• Glenohumeral joint: ball-and-socket synovial joint between the glenoid cavity and the head of the humerus

Ligaments of the Shoulder Girdle

• Acromioclavicular ligament: strengthens the AC joint

• Coracoclavicular ligament: divided into conoid and trapezoid ligaments, anchors the clavicle to the coracoid process

• Glenohumeral ligaments: strengthen the anterior aspect of the capsule

• Transverse humeral ligament: holds the long head of the biceps tendon in place

• Coracoacromial ligament: forms the coracoacromial arch, prevents superior displacement of the humerus

• Subacromial bursa: located between the acromion, coracoacromial ligament, and rotator cuff

• Subcoracoid bursa: located between the anterior surface of the subscapularis and the coracoid process

Muscles of the Shoulder Girdle

Origins, Insertions, Blood Supply, Innervation, and Actions

The shoulder girdle is moved and stabilized by several muscles, each with specific origins, insertions, blood supply, innervation, and actions.

Muscle	Origin	Insertion	Blood Supply	Innervation	Action
Subclavius	First rib and costal cartilage	Subclavian groove of clavicle	Clavicular branch of thoracoacromial artery, suprascapular artery	Subclavian nerve (C5, C6)	Depresses and stabilizes clavicle
Pectoralis major	Sternum, clavicle, costal cartilages	Lateral lip of intertubercular groove of humerus	Thoracoacromial trunk	Medial and lateral pectoral nerves (C5, C6, C7, C8, T1)	Adducts and medially rotates humerus
Pectoralis minor	3rd-5th ribs near costal cartilages	Coracoid process of scapula	Thoracoacromial artery	Medial pectoral nerve (C8, T1)	Stabilizes scapula by drawing it inferiorly and anteriorly
Serratus anterior	External surfaces of ribs 1-8	Medial border of scapula	Lateral thoracic artery	Long thoracic nerve (C5, C6, C7)	Protracts and rotates scapula
Levator scapulae	Transverse processes of C1-C4	Superior part of medial border of scapula	Dorsal scapular artery	Dorsal scapular nerve (C5)	Elevates scapula
Trapezius	Occipital bone, nuchal ligament, spinous processes of C7-T12	Lateral third of clavicle, acromion, spine of scapula	Transverse cervical artery	Accessory nerve (CN XI)	Elevates, retracts, and rotates scapula
Rhomboid major	Spinous processes of T2-T5	Medial border of scapula	Dorsal scapular artery	Dorsal scapular nerve (C5)	Retracts scapula
Rhomboid minor	Spinous processes of C7-T1	Medial border of scapula	Dorsal scapular artery	Dorsal scapular nerve (C5)	Retracts scapula
Latissimus dorsi	Spinous processes of T7-T12, thoracolumbar fascia, iliac crest	Intertubercular groove of humerus	Thoracodorsal artery	Thoracodorsal nerve (C6, C7, C8)	Extends, adducts, and medially rotates humerus

Summary Table: Brachial Plexus Organization

Component	Details
Roots	C5, C6, C7, C8, T1
Trunks	Superior (C5, C6), Middle (C7), Inferior (C8, T1)
Divisions	Each trunk splits into anterior and posterior divisions
Cords	Lateral, Posterior, Medial
Terminal Branches	Musculocutaneous, Median, Ulnar, Radial, Axillary

Key Equations and Concepts

• Synovial Joint Movement: The range of motion in a ball-and-socket joint is described by the degrees of freedom, typically three (flexion/extension, abduction/adduction, rotation).

• Blood Flow Equation: $Q = \frac{\Delta P}{R}$, where $Q$ is blood flow, $\Delta P$ is pressure difference, and $R$ is resistance.

Additional info:

• Some muscle origins and insertions were expanded for clarity.

• Blood supply and innervation details were inferred from standard anatomical sources.

• Joint and ligament functions were described for academic completeness.