The triceps, along with the biceps, are responsible for most powerful forearm movements. The triceps is a three-headed structure and is the only muscle located on the posterior upper arm. The three heads include the long head, the lateral head and the medial head. The three heads originate at different spots, but attach to the same tendon that inserts at the olecranon process of the ulna. The places of origin include:

* Long head – lower edge of the glenoid cavity of the scapula 

* Lateral head – posterior humerus

* Short head – distal two-thirds of the posterior humerus