Lateral head of triceps brachii

At a glance

English

Lateral head of triceps brachii

Latin (TA2)

Caput laterale musculi tricipitis brachii

System

Muscle

Region

Upper limb

Side

Paired, left and right

About the lateral head of triceps brachii

Triceps brachii is the large muscle filling the back of the arm and the main extensor of the elbow. It has three heads. The lateral head lies on the outer side of the back of the arm, superficial to the medial head, and together with the long head it forms the visible bulge just below the deltoid.

This head arises from a narrow oblique strip on the posterior surface of the humerus, running from just below the greater tubercle to the upper edge of the radial groove, and from the lateral intermuscular septum. Its fibres run down and medially and join the long head in a broad flat tendon over the lower half of the arm. The medial head attaches to the deep surface of the same tendon, which ends on the upper surface of the olecranon of the ulna and sends a slip into the forearm fascia.

Working with its partners, the lateral head extends the elbow. It is called into action mainly when force is needed, as in pushing up from a chair or throwing, while the medial head does most of the work in light extension. It is supplied by a branch of the radial nerve that leaves the nerve in the arm, and its blood comes from the deep artery of the arm, the profunda brachii, and the posterior circumflex humeral artery.

The radial nerve and the deep artery of the arm run in the radial groove beneath this head, between its origin and that of the medial head. A fracture of the humeral shaft can injure the nerve here, giving a wrist drop. The triangular interval, through which the nerve passes to the back of the arm, is bordered in part by the lateral head and the humerus.

Attachments, action and supply

Origin

Posterior surface of the humerus above the radial groove, and the lateral intermuscular septum.

Insertion

Olecranon of the ulna through the common triceps tendon, with a slip to the antebrachial fascia.

Action

Extends the elbow, especially against resistance.

Nerve supply

Radial nerve (C6, C7, C8).

Blood supply

Deep artery of the arm and the posterior circumflex humeral artery.