Triceps Brachii

Origin, Insertion, Action & Nerve

Attachments explained

The Triceps Brachii 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 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 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, 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 (the OIANS method)

OIANS stands for Origin, Insertion, Action and Nerve, the four facts that uniquely define every skeletal muscle. To learn the Triceps Brachii, work through them in order: picture its origin, trace the muscle to its insertion, reason out the action that shortening between those two points must create, then add the nerve that drives it.

Most students remember the Triceps Brachii fastest by linking its action back to its attachments rather than memorising each fact in isolation. Once the origin and insertion make sense, the action usually follows logically.

Triceps Brachii quick facts

Region

Upper Limb

Group

Arm

Origin

Long head: infraglenoid tubercle of scapula; Lateral head: posterior humerus above radial groove; Medial head: posterior humerus below radial groove

Insertion

Olecranon process of ulna

Action

Extension of forearm at elbow; long head extends and adducts arm

Nerve

Radial nerve (C6, C7, C8)

Spinal roots

C6, C7, C8

Frequently asked questions

Related muscles