Medial head of triceps brachii

At a glance

English

Medial head of triceps brachii

Latin (TA2)

Caput mediale musculi tricipitis caput brachii

System

Muscle

Region

Upper limb

Side

Paired, left and right

About the medial head of triceps brachii

Triceps brachii has three heads, and the medial head is the deepest. It lies against the back of the humerus, largely hidden by the long and lateral heads, and shows on the surface only near the elbow on each side of the common tendon. Despite its name it covers much of the width of the back of the bone.

It arises from a broad area of the posterior humerus below the radial groove, reaching nearly down to the olecranon fossa, and from both the medial and lateral intermuscular septa. Its fibres pass down to the deep surface of the common triceps tendon, which ends on the olecranon. Some of its deepest fibres attach to the posterior capsule of the elbow joint; this small slip, the articularis cubiti, lifts the capsule clear when the joint straightens so that it is not pinched.

The medial head is the workhorse of elbow extension. It is active in every extending movement, whether light or forceful, while the other two heads join in mainly when more force is needed. Its nerve supply comes from the radial nerve, including a long slender branch that runs with the ulnar nerve for part of its course. Its blood comes from the deep artery of the arm, its middle collateral branch and the superior ulnar collateral artery.

Because the radial nerve runs in its groove between this head and the lateral head, the medial head is often spared when the nerve is damaged in the groove, so elbow extension may survive a shaft fracture. The ulnar nerve passes along its medial side behind the medial epicondyle.

Attachments, action and supply

Origin

Posterior surface of the humerus below the radial groove, and the medial and lateral intermuscular septa.

Insertion

Olecranon of the ulna through the deep part of the common triceps tendon, with fibres to the elbow capsule.

Action

Extends the elbow in all extending movements; draws the joint capsule clear.

Nerve supply

Radial nerve (C6, C7, C8).

Blood supply

Deep artery of the arm, its middle collateral branch, and the superior ulnar collateral artery.