Triceps brachii

The triceps brachii (Latin: musculus triceps brachii) is a sizable three-headed muscle of the upper limb. It is located in the posterior compartment of the upper arm together with the anconeus muscle. The triceps brachii arises from two bones - the scapula and humerus. It extends almost the entire length of the humerus and inserts on the ulna. The triceps brachii is composed of three heads - long, lateral and medial. It is the primary forearm extensor.

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Triceps brachii
Origin

Long head - infraglenoid tubercle of scapula

Lateral head - posterior surface of humerus superior to radial groove

Medial head - posterior surface of humerus inferior to radial groove

InsertionOlecranon of ulna
Action

Entire muscle - extension of forearm

Long head - extension and adduction of arm

InnervationRadial nerve (C6 - C8)
Blood supply Deep brachial and superior ulnar collateral arteries

Origin

All three heads of the muscle have different origin sites:

  • Fibers of the long head of the triceps brachii originate from the infraglenoid tubercle of the scapula.
  • Fibers of the lateral head arise from the posterior surface of the humerus superior to the radial groove.
  • And finally, the fibers of the medial head originate from the posterior surface of the humerus inferior to the radial groove.
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Insertion

Fibers of all three heads merge and form a single tendon that inserts on the olecranon of the ulna.

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Action

The primary function of the triceps brachii muscle is the extension of the forearm at the elbow joint. Also, the long head provides the extension and adduction of the arm at the shoulder joint.

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Innervation

The triceps brachii is innervated by the radial nerve (C6 - C8) - a branch of the brachial plexus.

Blood supply

The triceps brachii muscle receives arterial blood from the deep brachial and superior ulnar collateral arteries. Both are branches of the brachial artery.