Arm Muscle Origins and Insertions

Below is a recap of what I've learned about the construction of the arm.

The biggest bother for me has been the brachioradialis. When the forearm is pronated but the brachioradialis is relaxed, the muscle seems to fold in a bizarre fashion that threw me until I revisited Eliot Goldfinger's book. This muscle will take some getting used to, but I think I have the rest of the arm pretty well memorized. Once I focused my attention to the influence that epicondyles had on the behavior of flexors and extensors, everything clicked. But when I attempted to show this visually by drawing it, I decided it would be clearer to simply describe the origins and insertions with text. So, below is a short list of what I now know about the surface muscles of the arm. I'll be referring back to this list for future figures, but I consider my study of the shoulder and elbow to be more-or-less complete. What remains is to work the knowledge into future figures so that I truly understand how these muscles move.

For the next week, I'll study the hand and try to memorize the names of the mess of flexors and extensors in the forearm.

Scapula

Height = Half the height of head.

Width = Approximately width of head.

Supraspinatus (Deep) originates on medial edge of scapula above spine of scapula and inserts through acromion process onto top of head of humerus.

Infraspinatus originates below spine of scapula on media edge down to Teres Major and inserts onto head of humerus.

Teres Minor originates between Infraspinatus and Teres Major on lateral edge of scapula and inserts onto head of humerus, below Infraspinatus.

Teres Major originates on medial end of bottom of scapula and inserts onto opposite side of humerus (~1/4 way down).

Humerus

Length = Height of head.

Deltoid -- Posterior origins start at edge of Trapezius (~1/8 way down spine of scapula), Acromial origins wrap across acromial process, Anterior origins end 1/3 of way across clavicle. Each inserts onto deltoid tuberosity (opposite radial groove).

Triceps -- Lateral and Medial heads originate ~1/6 of way down humerus, Long head originates from lateral edge of scapula, next to Teres Minor. Each inserts onto olecranon process (elbow). Triceps tendon starts ~1/3 way down humerus, creating noticeable flat indentation down to elbow when strained.

Biceps -- Both originate from coracoid process and insert onto radial tuberosity (just past head of radius). Long head originates through intertubercular groove.

Coracobrachialis originates from coracoid process and inserts into radial groove (opposite deltoid tuberosity, 1/2 way down humerus).

Brachialis originates 1/2 way down anterior humerus, just below deltoid tuberosity), and inserts just past olecranon process onto ulna.

Pronator Teres originates from medial epicondyle of humerus and inserts 1/2 way down radius. Twisting of forearm strains Pronator Teres, which in turn pulls on Bicipital Aponeurosis (stretching biceps).

Ulna

Length = Height of head.

Shape = Slight S-curve

Does not rotate.

Compresses muscles during extreme flexion of forearm.

Radius

Length = Height of head.

Shape = Slight C-curve

Rotates around ulna.

Brachioradialis + Extensor Carpi Radialis Longus both originate from lateral epicondyle of humerus to ~1/4 up humerus, between triceps and brachialis. Bracioradials inserts onto radial styloid process. Radialis Longus inserts onto posterior side of index metacarpal.

Flexor group (fingers) originates from medial epicondyle of humerus and inserts onto styloid process of ulna across onto posterior center of wrist.

Extensor group (fingers) originates from lateral epicondyle of humerus and inserts onto styloid process of radius across anterior wrist onto styloid process of ulna.

(Both epicondyles of humerus pull groups upon flexion and push groups upon extension of forearm.)

Abductor Pollicis Longus and Brevis originate 1/2 of way up radius (spanning 1/3 of radius) and insert past head of ulna onto end of thumb.