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Triceps brachii muscle

The posterior aspect of the arm is unique in that this compartment contains only one muscle, the triceps brachii muscle. The physical characteristics of the muscle (tri = three, cep = head) and its location (brachii = arm/upper arm) are given in its name; however, it’s functional importance, as part of the passageway for neurovascular structures to reach the posterior arm, requires a deeper understanding of the muscle.

This article will first detail the anatomy of the triceps brachii, including its bony attachments (origin and insertion), the movements it produces, and its innervation and blood supply. It will then discuss the involvement of the triceps brachii in the creation of spaces through which neurovascular bundles reach the posterior arm and forearm. Finally, these details will be discussed in relationship to clinical implications of the triceps muscle in arm injuries.

Key Facts
Origin Long head - infraglenoid tubercle of the scapula
Medial head - posterior surface of the humerus
Lateral head - posterior surface of the humerus
Insertion Olecranon
Action Extension of the forearm and elbow joint
Innervation Radial nerve

Triceps Brachii Anatomy

Origin and Insertion

From its name, we expect this muscle to have three separate bony origins, and subsequently three muscle bellies that come together to attach to a common insertion point.

Attachments of the triceps brachii muscle
Origin Long head: infraglenoid tubercle; located below the glenoid cavity on the scapula
Medial head: posterior surface of the humerus, inferior to the radial groove
Lateral head: posterior surface of the humerus, superior to the radial groove
Insertion The common tendon will attach to the proximal end of the olecranon of the ulna, and blend with the fascia of the proximal forearm. 

Actions

Because the triceps has three heads, each will have slightly different actions. However, when working together, the triceps is the main extensor of the forearm.

  • Long head – Because its origin attaches to the scapula, the long head will also act on the glenohumeral or shoulder joint. When the arm is adducted, the triceps muscle can act to pull superiorly on the humerus, helping to hold the head of the humerus in the glenoid cavity or resisting inferior displacement of the humerus. The long head will also create extension and adduction of the arm at the glenohumeral joint. In addition, like the lateral head, the long head of the triceps brachii is active during extension of the forearm that occurs against resistance. 
  • Medial head – Does not attach to the scapula and therefore, does not act on the glenohumeral joint. However, it is active whenever forearm extension is occurring, whether it is against resistance or not, and regardless of whether the forearm is pronated or supinated.
  • Lateral head – It is considered to be the strongest of the three heads but is typically only active during extension at the elbow that occurs against resistance.

Innervation and Blood Supply

All muscles located on the posterior aspect of the arm and forearm are supplied by the radial nerve. The radial nerve arises from the posterior cord (situated behind the brachial artery) of the brachial plexus, which forms within the anterior aspect of the axilla. The radial nerve enters the posterior aspect of the arm through the triangular interval (described in the next section), medial to the humerus and anterior to the long head of triceps, giving off branches to the long and medial heads as it does.

The radial nerve, along with the profunda brachii artery (which supplies the muscles in the posterior arm), then course inferolaterally, passing behind the humerus in the radial groove and between the medial and lateral heads of the triceps. The branch supplying the lateral head will arise from the radial nerve as it runs in the radial groove.

Passageways to the Posterior Upper Limb

The majority of the nerves that supply the muscles of the upper limb form anteriorly to the scapula and glenohumeral joint. They branch from the brachial plexus, and many of them remain on the anterior aspect of the limb and supply muscles in the anterior compartments of the arm and forearm.

Recommended video: Triceps brachii muscle
Origin, insertion and innervation of the triceps brachii muscle.

However, neurovascular structures also need to supply a number of muscles on the posterior aspect of the scapula, and the muscles on the posterior aspect of the arm and forearm. Therefore, passageways are needed in order for these structures to pass from anterior to posterior. The positioning of the triceps brachii allows the long head of the muscle to make up one of the borders of these passageways. 

The passageway spaces with their borders and contents are as follows: 

Quadrangular Space  

Boundaries and contents
Boundaries Superior border - inferior margin of the teres minor muscle.
Inferior border - superior margin of the teres major muscle.
Lateral border - surgical neck of the humerus.
Medial border - lateral margin of the long head of triceps brachii muscle.
Contents

Axillary nerve

Posterior circumflex humeral artery and vein

Triangular Space

Boundaries and Contents
Boundaries Superior border - inferior margin of the teres minor muscle.
Inferior border - superior margin of the teres major muscle.
Lateral border – medial margin of the long head of triceps brachii muscle.
Medial border – blending of teres major and minor muscles.
Contents Circumflex scapular artery and vein.

Triangular Interval (the most distal of the three)

Boundaries and contents
Boundaries Superior border - inferior margin of the teres major muscle.
Inferior border – shaft of the humerus and the medial head of triceps origin.
Lateral border – shaft of the humerus.
Medial border – lateral margin of the long head of triceps brachii muscle.
Contents Radial nerve
Profunda brachii artery and veins

Clinical Notes

It is important to test the integrity of the radial nerve when injuries occur on/or around the arm. A proximal arm injury may completely paralyze all three heads of the triceps muscle and severely limit extension of the forearm, especially against resistance. An injury to the midshaft of the humerus, for example a fracture, can damage the radial nerve as it runs in the radial groove. This injury placement may spare much of the functioning of the triceps muscle and forearm extension may only be weakened, but the patient may present with “wrist drop” due to the paralysis of muscles that extend the wrist.
 
Any tendon is susceptible to injury; the triceps tendon attachment to the olecranon is no exception. Any activity that overuses the triceps muscle can cause the tendon to become inflamed and damaged, resulting in pain and swelling near the muscle’s attachment to the olecranon.

Triceps brachii muscle - want to learn more about it?

Our engaging videos, interactive quizzes, in-depth articles and HD atlas are here to get you top results faster.

Sign up for your free Kenhub account today and join over 852,397 successful anatomy students.

“I would honestly say that Kenhub cut my study time in half.” – Read more. Kim Bengochea Kim Bengochea, Regis University, Denver

Show references

References:

  • R. L. Drake, A. W. Vogle, A. W. M. Mitchell: Gray’s Clinical Anatomy for Students, 3rd edition, Churchill Livingstone (2015), p. 717-721, 730-731, 763.
  • D. Landin, M. Thompson, M. Jackson: Functions of the Triceps Brachii in Humans: A Review, Journal of Clinical Medicine Research (2018), 10(4), 290-293.
  • K. L. Moore, A. D. Dalley II, A. M. R. Agur: Clinically Oriented ANATOMY, 7th edition, Lippincott Williams & Wilkins (2014), p. 735-738, 742-743.

Author:

  • Carolyn Perry
  • Francesca Salvador
  • Adrian Rad
© Unless stated otherwise, all content, including illustrations are exclusive property of Kenhub GmbH, and are protected by German and international copyright laws. All rights reserved.

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Muscles of the arm and the shoulder

Main muscles of the upper extremity

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