Triceps Brachii (*Triceps)

Origin, Insertion, Action & Nerve

Attachments explained

The Triceps Brachii (*Triceps) is defined first by where it attaches. Its origin is the more fixed anchor, usually the proximal or more stable end that stays put during contraction, while its insertion is the more mobile point that is pulled toward the origin when the muscle shortens.

Action & function

When the Triceps Brachii (*Triceps) contracts, it produces the following movements: Extension of forearm at elbow; long head extends and adducts arm.

As part of the Arm group of the Upper Limb, it works alongside neighbouring muscles to generate smooth, coordinated movement and to stabilise the structures it acts on.

Nerve supply & clinical relevance

The Triceps Brachii (*Triceps) receives its nerve supply from the Radial nerve (C6, C7, C8). This nerve carries fibres from spinal segment(s) C6, C7, C8.

Because a muscle can only contract when its nerve is intact, injury to the Radial nerve or to its spinal roots (C6, C7, C8) can weaken or paralyse the Triceps Brachii (*Triceps), impairing the movements it normally produces (extension of forearm at elbow). This is why knowing the innervation is central to localising nerve lesions in clinical practice.

How to study the Triceps Brachii (*Triceps) (the OIANS method)

Organise the triceps by its three heads and one tendon: whatever the origins, all fibres end on the olecranon, so the muscle's core job is elbow extension, the direct opposite of the biceps and brachialis in front. Only the long head reaches the scapula, which is why it alone also acts at the shoulder.

Use the radial groove of the humerus to link muscle and nerve: the radial nerve runs in that groove between the lateral and medial heads, so a mid-shaft humeral fracture threatens both the nerve and triceps function. That single relationship ties together the origins, the nerve supply, and the classic clinical deficit of wrist drop.

Frequently asked questions

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