Prepare me a table including the muscles of upper arm, their origin and insertion and main points to remember if any
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I now have all the information needed. Let me compile the comprehensive table.
Here is a complete table of the muscles of the upper arm, drawn from Gray's Anatomy for Students and Miller's Review of Orthopaedics.
Muscles of the Upper Arm
The upper arm has two compartments: anterior (flexors) and posterior (extensor), separated by the medial and lateral intermuscular septa.
Anterior Compartment (3 muscles)
| Muscle | Origin | Insertion | Innervation (Spinal Level) | Action | Key Points |
|---|---|---|---|---|---|
| Coracobrachialis | Apex of coracoid process of scapula | Linear roughening on medial aspect of midshaft of humerus | Musculocutaneous nerve (C5, C6, C7) | Flexion and adduction of arm at glenohumeral joint | - The musculocutaneous nerve pierces this muscle to enter the arm - it is the only muscle in the arm pierced by its nerve. Highest spinal level tested is C7. |
| Biceps brachii | - Long head: supraglenoid tubercle of scapula - Short head: apex of coracoid process (with coracobrachialis) | Radial tuberosity; also gives off bicipital aponeurosis to deep fascia of forearm | Musculocutaneous nerve (C5, C6) | - Most powerful supinator of forearm (when elbow is flexed) - Powerful flexor of forearm at elbow - Accessory flexor of arm at glenohumeral joint | - Tendon of the long head passes intra-articularly through the glenohumeral joint, held in the intertubercular sulcus by the transverse humeral ligament - Long head prevents superior subluxation of humerus - Bicipital aponeurosis protects brachial artery and median nerve - Rupture of long head tendon causes "Popeye sign" (prominent muscle belly bulge on flexion) - Biceps reflex tests C6 - Most powerful supinator only when elbow is already flexed (unlike supinator muscle which works at any angle) |
| Brachialis | Distal half of anterior surface of humerus (medial and lateral surfaces) and adjacent intermuscular septa | Tuberosity of ulna | Musculocutaneous nerve (C5, C6); small contribution from radial nerve (C7) to lateral part | Powerful flexor of forearm at elbow (the true workhorse flexor) | - Lies deep to biceps brachii - Only crosses the elbow joint (not the shoulder), making it a pure elbow flexor - Called the "workhorse of elbow flexion" - Dual nerve supply (musculocutaneous + radial) is clinically important; paralysis of one nerve does not completely eliminate flexion - Inserts into ulna (not radius), so it flexes the forearm regardless of pronation/supination position |
Posterior Compartment (1 muscle, 3 heads)
| Muscle | Origin | Insertion | Innervation (Spinal Level) | Action | Key Points |
|---|---|---|---|---|---|
| Triceps brachii | - Long head: infraglenoid tubercle of scapula - Lateral head: posterior surface of humerus, superior to radial groove (linear roughening) - Medial head: posterior surface of humerus, inferior to radial groove (extensive area) | Superior surface of olecranon of ulna | Radial nerve (C6, C7, C8) | - Extension of forearm at elbow - Long head can also extend and adduct the arm at glenohumeral joint | - Only muscle in the posterior compartment of the arm - The radial nerve and profunda brachii artery run in the radial groove (spiral groove) between the lateral and medial heads - Saturday night palsy / crutch palsy: compression of radial nerve in the radial groove causes wrist drop; triceps is usually spared because its branches come off before the groove - Triceps reflex tests C7 - Long head is the only head that crosses the shoulder joint - Medial head is the "workhorse" of extension (deepest, most active at all positions) |
Quick Memory Summary
| Feature | Anterior Compartment | Posterior Compartment |
|---|---|---|
| Muscles | Coracobrachialis, Biceps brachii, Brachialis | Triceps brachii |
| Main nerve | Musculocutaneous nerve | Radial nerve |
| Primary action | Elbow flexion + supination | Elbow extension |
| Reflex tested | Biceps - C6; (Brachioradialis - C5) | Triceps - C7 |
| Compartment borders | Medial + lateral intermuscular septa | Same septa |
Sources: - Gray's Anatomy for Students (Tables 7.8, 7.9, pp. 874-875) - Miller's Review of Orthopaedics, 9th Ed. (Table 2.5, p. 145)
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