Muscles That Move the Pectoral Girdle, Arm, and Forearm

Muscles That Move the Pectoral Girdle

• Definition
• "Pectoral girdle movers" = muscles whose primary insertion is on the scapula and/or clavicle, causing those bones to reposition.
• Motion created indirectly affects humeral position but the muscle itself does not cross the glenohumeral joint.

• Levator Scapulae
• Origin: Transverse processes of upper cervical vertebrae.
• Insertion: \text{Superior angle of the scapula}.
• Action: Elevates/superiorly rotates scapula (used in shrugging or tilting glenoid cavity downward).

• Rhomboids (Rhomboideus Major & Minor)
• Naming = rhomboid (diamond shape) + size.
• Origin (both): Spinous processes of C7–T5.
• Insertions:
• Minor – medial border at root of scapular spine.
• Major – medial border inferior to scapular spine.
• Actions: Scapular retraction (adduction) & downward rotation.
• Relationship: Minor is superior, Major is inferior (“little on top of big”).

• Trapezius (Portion acting on girdle)
• Kite-shaped; fibers orient ascending, transverse, descending → 3 lines of pull.
• Origins: Occipital bone + nuchal ligament + spinous processes C7–T12.
• Insertions: Clavicle (lateral 1/3), acromion, spine of scapula.
• Actions:
• Upper fibers – elevate scapula.
• Middle fibers – retract scapula.
• Lower fibers – depress & superiorly rotate scapula.
• Indirect role in arm elevation because it positions the glenoid cavity for deltoid activity.

• Serratus Anterior (“Hugging muscle”)
• Recognition: Serrated/jagged edge on lateral thorax.
• Origin: Outer surfaces of ribs 1–8/9.
• Insertion: Anterior surface of medial border and inferior angle of scapula (wraps posteriorly).
• Actions: Protraction (reaching forward), upward rotation (glenoid faces superiorly). Essential in punching & push-ups.
• Clinical link: Paralysis → medial winging of scapula.

• Pectoralis Minor
• Origin: Ribs 3–5.
• Insertion: Coracoid process of scapula.
• Actions: Tilts scapula anteriorly & depresses it; accessory muscle of inspiration when scapula fixed.

• Misc. / Context
• Erector spinae group (spinalis, longissimus, iliocostalis) sits deep & medial – included for orientation.
• Rotatores muscles briefly shown but not tested.

Muscles That Move the Arm (Glenohumeral Joint)

• Deltoid
• Origins: Spine of scapula, acromion, lateral clavicle.
• Insertion: \text{Deltoid tuberosity (humerus)}.
• Actions by part: Anterior – flexes/medially rotates; Middle – abducts (prime mover beyond 15^{\circ}); Posterior – extends/laterally rotates.

• Latissimus Dorsi
• Origin: Thoracolumbar aponeurosis (spinous processes T7–L5, sacrum), iliac crest, lower ribs.
• Insertion: Floor of intertubercular sulcus (anterior humerus).
• Actions: Extension, adduction, medial rotation of arm; powerful "pull-down" (e.g., swimming, climbing).
• Visual cue: Creates swimmer’s “V-shape.”

• Pectoralis Major
• Origin: Medial clavicle, sternum, costal cartilage 1–6.
• Insertion: Lateral lip of intertubercular sulcus.
• Actions: Flexion, adduction, medial rotation; used in push-ups/bench press.

• Teres Major ("Lat’s little helper")
• Origin: Inferior angle/posterior surface of scapula.
• Insertion: Medial lip of intertubercular sulcus (anterior humerus).
• Action: Same as latissimus – extension, adduction, medial rotation; important for internal rotation (thumb turns downward).

• Coracobrachialis
• Origin: Coracoid process of scapula.
• Insertion: Medial humeral shaft (mid-diaphysis).
• Actions: Assists arm flexion & adduction; stabilizes GH joint.

• Rotator Cuff (SITS)
• Supraspinatus – initiates 0–15^{\circ} abduction; origin: supraspinous fossa; passes under acromion.
• Infraspinatus – lateral rotation; origin: infraspinous fossa; posterior insertion on greater tubercle.
• Teres Minor – lateral rotation; origin: lateral scapular border; inserts just inferior to infraspinatus.
• Subscapularis – medial rotation; origin: subscapular fossa (anterior scapula); inserts on lesser tubercle.
• Collectively form musculotendinous cuff encircling humeral head → shoulder stability.

Muscles That Move the Forearm (Elbow Joint)

• Biceps Brachii (2 heads)
• Long head origin: Supraglenoid tubercle.
• Short head origin: Coracoid process.
• Insertion: Radial tuberosity & bicipital aponeurosis to ulna fascia.
• Actions: Forearm flexion (primary when supinated), powerful supination, weak shoulder flexion.

• Brachialis (deep to biceps)
• Origin: Anterior distal half of humerus.
• Insertion: Ulnar tuberosity & coronoid process.
• Action: Pure elbow flexor in all positions (workhorse).

• Brachioradialis
• Origin: Lateral supracondylar ridge (humerus).
• Insertion: Styloid process of radius.
• Action: Flexes forearm, strongest in mid-pronation (handshake position); useful landmark dividing flexor/extensor forearm compartments.

• Triceps Brachii (3 heads)
• Long head origin: Infraglenoid tubercle (scapula).
• Lateral & Medial heads origin: Posterior humeral shaft (superior & inferior to radial groove respectively).
• Insertion: Olecranon process (ulna).
• Action: Forearm extension (medial head workhorse, long head also extends/adducts arm).

• Anconeus
• Origin: Lateral epicondyle of humerus.
• Insertion: Lateral olecranon & proximal ulna.
• Action: Assists triceps in extension; stabilizes elbow during pronation-supination.

Pronators & Supinators (Radius ↔ Ulna Rotators)

• Pronator Teres
• Origin: Medial epicondyle (humerus) & coronoid process (ulna).
• Insertion: Lateral mid-shaft of radius.
• Action: Rapid, powerful pronation; weak elbow flexor.

• Pronator Quadratus (deep wrist layer)
• Origin: Distal anterior ulna.
• Insertion: Distal anterior radius.
• Action: Primary pronator for slow, unopposed movements; stabilizes distal radioulnar joint.

• Supinator
• Origin: Lateral epicondyle of humerus, radial collateral & annular ligaments, supinator crest of ulna.
• Insertion: Proximal 1/3 of radius (posterior, lateral, anterior surfaces).
• Action: Unresisted supination (especially when elbow extended); biceps supplies power when elbow flexed.

• Functional Opposites
\text{Pronators (anterior fibers) } \longleftrightarrow \text{ Supinator (posterior fibers)}
• Pronator fibers run obliquely antero-lateral → posterior pulling radius over ulna.
• Supinator fibers run postero-lateral → anterior uncrossing radius.

Key Visual & Palpation Landmarks (from models)

• Serratus anterior – visible between pectoral region & latissimus; serrated slips.
• Inferior angle tug test: Pulling this angle anteriorly demonstrates serratus action (“hug”).
• Thoracolumbar aponeurosis – shiny, flat tendon inferior to latissimus; landmark for lat origin.
• Intertubercular groove – houses biceps long-head tendon; lat/T. major/pec major wrap to attach here (med → lat lip sequence).
• Supraspinatus passage – travels beneath acromion; narrow space prone to impingement.

Integrated Actions & Real-World Relevance

• Swimming pull-down: Latissimus + T. major extend/adduct against water resistance.
• Throwing (cocking phase): Rhomboids retract, rotator cuff stabilizes, deltoid abducts.
• Punching/Boxing: Serratus anterior protracts; triceps extend elbow.
• Push-ups: Pectoralis major & minor, serratus anterior (scapular stability), triceps.
• Clinical: Rotator cuff tears often at supraspinatus tendon; winged scapula indicates long thoracic nerve lesion affecting serratus.

Connections to Previous Content

• Erector spinae group shares deep back region; posture influences scapular base for deltoid & rotator cuff.
• Semispinalis/spinalis capitis seen in earlier lecture—important for head posture during upper-limb tasks.

Numerical / Structural Quick Facts

• Triceps = 3 heads, Biceps = 2 heads.
• Rotator cuff = 4 muscles (SITS).
• Pronators vs. Supinators: 2 principal pronators, 1 primary supinator (+ biceps as dynamic supinator).
• Scapular motions: elevation, depression, protraction, retraction, upward & downward rotation = 6 fundamental directions.

Ethical / Practical Considerations

• Overuse injuries (eg, swimmer’s shoulder) highlight need for balanced strengthening of antagonistic groups (rhomboids vs. serratus).
• Rehabilitation protocols rely on understanding origin–insertion mechanics to train or off-load specific muscles (e.g., closed-chain serratus push-ups for scapular stability).