Origins & Insertions - Upper Extremity, Posterior

• We'll be looking at the right side.

• The bone that remains stable upon muscle contraction.

• The bone moves upon muscle contraction.

In the limbs, the origin is usually proximal to the insertion.

• Review key skeletal components:

Scapula Humerus, radius, ulna Hand

• Insertion sites of muscles that act on the scapula:

Trapezius inserts along the superior border of the spine and acromion; trapezius is a powerful muscle of the superficial back. From superior to inferior along the medial border of the scapula: Levator scapulae Rhomboid minor (medial to spine of scapula) Rhomboid major

• Origins of muscles that act on the upper arm:

Deltoid arises along the inferior border of the spine and acromion; deltoid is a powerful shoulder muscle. Supraspinatus arises superior to the scapular spine, within the supraspinatus fossa. Infraspinatus arises inferior to the spine, within the infraspinatus fossa. Along the lateral border, from superior to inferior: The long head of triceps brachii arises from the infraglenoid tubercle. Teres minor arises from two places: medial to the long head of triceps brachii and inferior to it. Teres major arises inferior to teres minor. Latissimus dorsi has a small point of origin on the inferior angle.

• Humeral insertions of these muscles, from superior to inferior

Three muscles insert on the greater tubercle: Supraspinatus inserts on the superior aspect of the greater tubercle. Infraspinatus inserts on the middle facet of the greater tubercle of the humerus. Teres minor inserts on the inferior facet of the greater tubercle. Deltoid inserts on the shaft of the humerus at the deltoid tuberosity.

• Origins of muscles that arise from the humerus and act on the forearm

From superior to inferior along the shaft: The lateral head of triceps brachii attaches superiorly to the radial groove. Brachialis, just distal to the insertion of deltoid. The medial head of triceps brachii arises inferior to the radial groove. The superficial head of supinator and the common extensor tendon arise from the lateral epicondyle. Anconeus arises from the lateral condyle. And, the common flexor tendon arises from the medial epicondyle.

• Insertion sites of muscles that act on the forearm:

Triceps brachii inserts on the olecranon process of the ulna. Anconeus inserts inferior to triceps brachii. Biceps brachii inserts on the radial tuberosity of the radius. The deep head of supinator arises from the crest of the ulna (the superficial head of supinator originates on the lateral condyle of the humerus).

• Insertion sites:

The deep head of supinator inserts along the lateral edge of the radius. Pronator teres and brachioradialis insert along the lateral side of the radius. Pronator teres inserts proximally, brachioradialis inserts distally.

• Origins of the wrist extensors in the forearm:

Abductor pollicis longus arises from the ulna, radius, and interosseous membrane. Extensor pollicis brevis originates on the radius and interosseous membrane, distal to abductor pollicis longus. Extensor pollicis longus originates from the ulna and interosseous membrane. Extensor indicis (indicis = index finger) also arises from the ulna and interosseous membrane. Extensor carpi ulnaris, (carpi = carpals), proximally on the posterior ulna. Flexor digitorum profundus (which is technically an anterior compartment muscle), medially. Flexor carpi ulnaris (another anterior compartment muscle), laterally.

• Insertions of these muscles in the hand, from lateral to medial:

Abductor pollicis longus on metacarpal I. Extensor carpi radialis longus on metacarpal II. Extensor carpi radialis brevis on metacarpal III. Extensor carpi ulnaris on metacarpal V. Extensor pollicis brevis on the base of the proximal phalanx of digit 1. Extensor pollicis longus on the base of the distal phalanx of digit 1. Extensor indicis inserts on the intermediate and distal phalanges of digit 2. Extensor digiti minimi on the intermediate and distal phalanges of digit 5. Extensor digitorum inserts on digits 2-5 via central bands (bases of intermediate phalanges) and lateral bands (bases of distal phalanges).