Quick Facts
Origin: Posterior surface of humerus and infraglenoid tubercle of scapula.
Insertion: Olecranon process of ulna and adjacent antebrachial fascia.
Action: Extends forearm at elbow joint.
Innervation: Radial nerve (C6-C8).
Arterial Supply: Deep brachial, superior ulnar collateral, and posterior circumflex humeral arteries.
Related parts of the anatomy
Origin
The medial and lateral heads of the triceps brachii muscle originate from the posterior surface of the humerus, where:
- the medial head originates from the area located inferior to the groove for radial nerve;
- the lateral head originates from the area located superior to the groove for radial nerve.
The long head originates from the infraglenoid tubercle of the scapula. The triceps brachii muscle also originates from the medial and lateral intermuscular septa of the arm.
Insertion
The fibers of the medial, lateral, and long heads of triceps brachii muscle all converge to a single triceps brachii tendon, which inserts onto both the superior end of the olecranon of the ulna and adjacent antebrachial fascia. Some fibers from the medial head of the triceps brachii muscle attach to the articular capsule of the elbow joint. These fibers, which by some, are considered an additional muscle in the arm known as the articularis cubiti muscle (or subanconeus).
Key Features & Anatomical Relations
The triceps brachii muscle is found in the posterior compartment of the arm. It is a fusiform type of skeletal muscle and is composed of three heads: medial, lateral, and long, where:
- the medial head is located deep to the lateral and long heads;
- the long head is located medial to the lateral head.
The triceps brachii muscle is located:
- posterior (superficial) to the deep brachial artery and radial nerve;
- lateral to the teres major and teres minor muscles.
Actions & Testing
The triceps brachii muscle extends the forearm at the elbow joint. This action is not affected by pronation or supination of the forearm. The medial head is active in the presence or absence of resistance, while the lateral and long heads are generally only active in the presence of resistance. The long head also assists in extension and stabilization of the glenohumeral (shoulder) joint.
The triceps brachii muscle can be tested by extending the forearm at the elbow joint against resistance, during which it can be palpated (Standring, 2016).
References
Standring, S. (2016) Gray's Anatomy: The Anatomical Basis of Clinical Practice. Gray's Anatomy Series 41st edn.: Elsevier Limited.
