Lateral Head of Triceps Brachii

Origin

The lateral head of triceps brachii muscle originates, via a flat tendon, from an oblique ridge found on the posterior surface of the humerus. This ridge is located superior to the groove for radial nerve. It also originates from the lateral intermuscular septum 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.

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.

Regarding the lateral head of triceps brachii specifically, its proximal end is located deep to the deltoid muscle.

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 lateral head is generally only active in the presence of resistance.

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.