W9 Bones of the Chest & Upper Limb; Muscles of the Back, Chest, and Shoulder Upper Limb Regions

Bones of the Chest & Upper Limb; Muscles of the Back, Chest, and Shoulder Upper Limb Regions

• Brachium (Arm proper): Shoulder to elbow
• Antebrachium (Forearm): Elbow to wrist
• Wrist & Hand: Includes carpus (wrist), metacarpals, and phalanges
• Connection to Trunk: By pectoral girdle (scapula & clavicle)

Pectoral Girdle: Scapula

• Flat bone, posterior-lateral thorax, over ribs 2–7
• Key features:
  • Borders: Superior, medial, lateral
  • Angles: Superior, inferior, lateral
  • Spine: Transverse ridge (posterior)
  • Supraspinous/Infraspinous fossae: Above/below spine
  • Subscapular fossa: Concave anterior surface
  • Acromion process: Lateral projection, forms shoulder apex, articulates with clavicle
  • Coracoid process: Muscle attachment site
  • Glenoid cavity: Shallow socket, articulates with humeral head
• Surrounded by muscle layers; fractures rare (mainly from trauma)

Pectoral Girdle: Clavicle

• S-shaped, long bone, first to ossify in embryo
• Medial 2/3 convex anteriorly; lateral 1/3 concave
• Medial end: Rounded, articulates with sternum
• Lateral end: Flattened, forms acromioclavicular joint
• Subcutaneous, acts as strut—keeps upper limb clear of trunk
• Most frequently fractured bone (usually at lateral/intermediate third junction)

Sternum

• Bony plate anterior to heart
• Three regions: Manubrium, body (gladiolus), xiphoid process
• Key landmarks: Jugular notch, sternal angle, articular facets for ribs 1–7

Humerus

• Proximal end:
  • Head articulates with glenoid cavity
  • Greater/lesser tubercles, intertubercular sulcus (biceps tendon), surgical neck
• Distal end:
  • Capitulum (articulates with radius), trochlea (with ulna)
  • Lateral/medial epicondyles, olecranon fossa (for ulna), coronoid & radial fossae
• Common fracture sites; possible nerve injuries (axillary, radial, musculocutaneous, ulnar)

Forearm (Antebrachium)

• Ulna (medial):
  • Olecranon (elbow point), trochlear notch (articulates with humerus), coronoid process
  • Radial notch (proximal radio-ulnar joint), head (distal), styloid process
• Radius (lateral):
  • Head (articulates with humerus & ulna), neck, radial tuberosity (biceps attachment)
  • Ulnar notch (distal, for ulna), styloid process (stabilises wrist)
• Interosseous membrane joins both

Wrist & Hand

• Wrist: 8 carpal bones (4 proximal, 4 distal); flexibility allows bending/twisting
• Carpal tunnel syndrome: Inflammation/compression of median nerve
• Hand:
  • 5 metacarpals (lateral to medial)
  • Phalanges: Thumb has 2, other fingers have 3 each (proximal, middle, distal)

Muscle Attachments

• Origin: Stationary attachment
• Insertion: Movable attachment
• Muscles attach to bone, fascia, tendon, or skin; crossing a joint allows action on that joint

Muscle Functional Groups

• Prime mover: Main force for movement
• Synergist: Aids prime mover
• Antagonist: Opposes prime mover; relaxes for movement control
• Fixator: Prevents bone movement
• Antagonistic pairs act on opposite joint sides

Muscles of Neck & Back

• Attach vertebral column, thoracic cage, pectoral girdle to skull/vertebral column
• Movements: Flexion, extension, lateral flexion, rotation
  • Erector spinae (superficial):
    • Spinalis, longissimus, iliocostalis groups
  • Erector spinae (deep):
    • Semispinalis, multifidus, interspinales, intertransversarii, rotatores
  • Spinal flexors:
    • Neck: Longus capitis, longus colli
    • Lumbar: Quadratus lumborum (flexes spine, depresses ribs)

Muscles of Chest & Upper Limb

• Pectoralis major:
  • Origin: Sternum, ribs, clavicle
  • Insertion: Humerus
  • Action: Arm flexion, adduction, medial rotation; used in climbing
• Pectoralis minor:
  • Origin: Ribs 3–5
  • Insertion: Coracoid process
  • Action: Depresses shoulder, accessory in respiration
• Serratus anterior:
  • Origin: Upper 8 ribs
  • Insertion: Medial border of scapula
  • Action: Scapula protraction, rotation; 'winged' scapula if weak
• Trapezius:
  • Origin: Nuchal lines, cervical/thoracic spines
  • Insertion: Clavicle, acromion, scapular spine
  • Action: Neck extension, scapula elevation/rotation, shoulder bracing
• Latissimus dorsi:
  • Origin: T6–12 spines, lower ribs, iliac crest, thoracolumbar fascia, scapula
  • Insertion: Humerus (anterior, intertubercular sulcus)
  • Action: Arm adduction, extension, medial rotation; raises body in climbing

Other Muscles of Shoulder/Back

• Levator scapulae:
  • Origin: C1–C4 transverse processes
  • Insertion: Upper medial scapula
  • Action: Scapula elevation, tilts glenoid down
• Rhomboid minor:
  • Origin: C7–T1/2 spines
  • Insertion: Medial scapula (opposite spine)
  • Action: Elevation, retraction of scapula
• Rhomboid major:
  • Origin: T2–T5 spines
  • Insertion: Medial scapula (below spine)
  • Action: Retraction, elevation of scapula

Deltoid (Shoulder Region)

• Origin:
  • Anterior: Clavicle
  • Middle: Acromion
  • Posterior: Spine of scapula
• Insertion: Humerus (deltoid tuberosity)
• Action:
  • All fibres: Abduction
  • Anterior: Flexion
  • Middle: Abduction
  • Posterior: Extension/hyperextension
  • Prevents dislocation when carrying weights

Rotator Cuff Muscles (Shoulder Stability)

• Supraspinatus:
  • Origin: Supraspinous fossa
  • Insertion: Upper greater tubercle
  • Action: Humerus abduction
• Infraspinatus:
  • Origin: Infraspinous fossa
  • Insertion: Middle greater tubercle
  • Action: Lateral rotation
• Teres minor:
  • Origin: Lateral scapula border
  • Insertion: Lower greater tubercle
  • Action: Lateral rotation
• Subscapularis:
  • Origin: Costal scapula surface
  • Insertion: Lesser tubercle
  • Action: Medial rotation
• Teres major:
  • Origin: Inferior angle/lateral border of scapula
  • Insertion: Medial lip of intertubercular sulcus
  • Action: Medial rotation