Final answer:
The triceps brachii originates from the long head, lateral head, and medial head.
Step-by-step explanation:
The triceps brachii is a three-headed muscle located on the posterior side of the upper arm that extends the forearm. It has three separate points of origin: the long head, the lateral head, and the medial head. The long head originates from the infraglenoid tubercle of the scapula, the lateral head originates from the posterior humerus above the radial groove, and the medial head originates from the posterior humerus below the radial groove.