CorpusHuman Anatomy
MuscularMuscle

Triceps brachii

Musculus triceps brachii

Also known as: triceps

The three-headed muscle of the back of the arm. It is the main extensor of the elbow, and its long head also extends and adducts the shoulder.

Show on body map Muscles — Posterior View

Overview

Triceps is the only muscle filling the posterior compartment of the arm.
- Long head: from the infraglenoid tubercle of the scapula. It crosses the shoulder, so it helps extend and adduct the arm.
- Lateral head: from the posterior humerus above the radial (spiral) groove.
- Medial head: from the posterior humerus below the radial groove. It lies deep and is active in all elbow extension.

The three heads join in a common tendon that inserts on the olecranon of the ulna and the posterior joint capsule.

The radial nerve and the profunda brachii artery spiral around the back of the humerus in the radial groove, between the lateral and medial heads, and supply all three heads. Because the branches to triceps leave the nerve high up (some in the axilla), mid-shaft humeral fractures usually spare triceps even when they cause wrist drop. The triceps reflex (C7, with C6–C8) is tested by tapping its tendon above the olecranon.

Location

Posterior compartment of the arm.

Parts & subdivisions

  1. Long head
    Infraglenoid tubercle. Crosses the shoulder joint. Separates the quadrangular and triangular spaces.
  2. Lateral head
    Posterior humerus above the radial groove.
  3. Medial head
    Posterior humerus below the radial groove. The deep "workhorse" head.

Anatomy

Origin

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

Insertion

Proximal end of the olecranon of the ulna and the posterior capsule of the elbow.

Action

Extension of the forearm at the elbow; long head also extends and adducts the arm at the shoulder.

Innervation

Radial nerve (posterior cord).

Nerve roots

C6–C8 (mainly C7)

Arterial supply

Deep brachial artery (profunda brachii); posterior circumflex humeral artery (long head); superior ulnar collateral artery.

Relations

The radial nerve and profunda brachii vessels run between the lateral and medial heads in the radial groove. The long head separates the quadrangular space from the triangular space and forms the triangular interval.

Function

  • Extends the elbow (prime mover)
  • Long head extends and adducts the arm
  • Stabilises the shoulder and the elbow when pushing

Clinical significance

Triceps reflex

Tests C7 (C6–C8) and the radial nerve. It is lost in C7 radiculopathy, which is common after C6–C7 disc herniation.

Saturday night palsy

Compression of the radial nerve in the radial groove (e.g. arm draped over a chair) causes wrist drop but usually spares triceps, because its branches arise proximal to the groove.

Compiled from standard anatomy and physiology references — see the Muscular System sources. For education only; not medical advice.