What does the muscle triceps brachii do?

The triceps brachii is a large muscle on the back of the upper arm (posterior arm). It consists of three heads: lateral head, medial head, and long head. The lateral head is the largest and most superficial of the three heads. The medial head is the smallest and is located deep to the lateral head. The long head originates from the scapula and is the only one of the three heads to cross the shoulder joint. All three heads of the triceps brachii insert onto the olecranon process of the ulna.

The main action of the triceps brachii is to extend (straighten) the arm at the elbow joint. This is an important movement in a variety of activities, such as throwing, pushing, and lifting. The triceps brachii also helps to stabilize the shoulder joint.

The triceps brachii is innervated by the radial nerve. The long head of the triceps brachii is innervated by the axillary nerve.