The triceps brachii is a large three-headed muscle of the posterior muscle group of the upper arm. It arises from two bones - scapula and humerus, and originates as three heads - long head, lateral head, and medial head. The medial head lies deeper covered by the other two heads of the triceps brachii.

Origin: fibers of the long head originate from the infraglenoid tubercle of the scapula, lateral head - from the posterior surface of the humerus above the radial groove, and medial head - from the posterior surface of the humerus below the radial groove.

Insertion: fibers of the three heads converge to a single tendon that inserts onto the olecranon process of the ulna.

Action: the entire muscle provides extension of the forearm; the long head of the triceps brachii also participates in both extension and adduction of the upper arm.

Innervation: radial nerve (C6 - C8).

Blood supply: deep brachial and superior ulnar collateral arteries, which are both branches of the radial artery.

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Triceps brachii muscle