Triceps brachii muscle

The triceps brachii muscle (triceps) is a muscle of the arm that straightens the elbow when contracted. It is also used to stabilize the shoulder.

The triceps is named because it has three distinct bundles of muscle that originate from three points - one on the scapula and two on the humerus. These bundles join near the insertion point at the elbow. It is innervated by the radial nerve.

The triceps is by far the largest muscle in the upper arm, usually accounting for 60-70% of the total muscle mass.

Origin
The triceps originates from the scapula (shoulder blade) and the humerus. The three heads of the triceps have separate origins.

The long head originates from the infraglenoid tubercle of the scapula; the lateral head from the upper half of the posterior of the humerus. The medial head originates from the lower half of the posterior of the humerus.

Insertion
The triceps inserts on the ulna, at the posterior part of the upper surface of the olecranon.

Innervation
The triceps is innervated by the radial nerve (C7 and C8).

Word origin
In Latin, triceps means three-headed, referring to the three sections of the muscle. Brachii means arm. So the triceps brachii muscle is the three-headed arm muscle.