Dr. Ebraheim’s educational animated video describes the anatomy associated with the triceps muscle.

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Anatomy of the Triceps Muscle
The triceps muscle is a powerful extensor of the elbow joint. The triceps muscle has three heads: the long head, the lateral head, and the medial head. All three heads of the triceps insert into the olecranon. The superficial part of the triceps is formed by the long and lateral heads, while the deep part is formed by the medial head alone. The long head arises from the scapula and stretches across the shoulder and elbow joint. The long head originates from the infraglenoid tubercle of the scapula and inserts into the proximal end of the olecranon process of the ulna. The lateral head originates from the posterior aspect of the humerus superior to the spiral groove and stretches across the elbow joint. The lateral head inserts into the proximal end of the olecranon process of the ulna. The medial head originates from the posterior aspect of the humerus inferior to the spiral groove and stretches across the elbow joint. The medial head inserts into the proximal end of the olecranon process of the ulna. All three heads of the triceps are inserted into the olecranon process. The insertion area is approximately 12 mm distal to the tip of the olecranon. The arterial supply of the triceps muscle comes from the branches of the deep brachial artery. The radial nerve supplies the triceps muscle and it comes from the posterior cord of the brachial plexus. The radial nerve runs through the spiral groove between the lateral head and the medial head of the triceps. 13 cm above the trochlea, the radial nerve pierces the lateral intermuscular septum approximately 7.5 cm above the trochlea. It is important to know the relationship between the radial nerve and the triceps. Three anatomical spaces bordered by the triceps are the quadrangular space, the triangular interval, and the triangular space. The quadrangular space is bound superiorly by the teres minor, inferiorly by the teres major, medially by the long head triceps, and laterally by the surgical neck humerus. It contains the axillary nerve and the posterior circumflex humeral artery. The triangular interval is bound by the teres major, the long head triceps, and the humeral shaft. The triangular interval contains the deep branch of brachial artery and the radial nerve. The triangular space is bound by the teres major, the teres minor, and the long head triceps. The triangular space contains the circumflex scapular artery. All three heads of the triceps are inserted into the olecranon process. Rupture of the distal triceps tendon can occur. It usually results from sports such as weight lifting and body building (seen in middle aged men). Risk factors for triceps tendon rupture include local injection of steroids of use of anabolic steroids, taking antibiotics (ciprofloxacin), and general systemic disease (rheumatoid arthritis, hyperparathyroidism, diabetes, and renal disease. Patients with triceps tendon rupture will not be able to extend the elbow or extension of the elbow will be weaker than the other side. The rupture usually occurs at the insertion site (may be partial or complete). The patient may hear a painful “pop” with rupture of the tendon. The “flake sign” which is an avulsion of a small piece of bone from the elbow sometimes is seen on a lateral xray. MRI is really the best study. Primary surgical repair of the tendon for acute complete tear or partial tear more than 50%. Reconstruction of the tendon by tendon graft in chronic, neglected cases, especially if the patient has a major disability in elbow extension (the result is not as good as in cases of acute repair. Excision of comminuted olecranon fracture fragments with reattachment of the triceps tendon in the elderly patient can be done with a reasonable result if the fragment size is less than 50%.