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Triceps Brachii – Functional Anatomy

The triceps brachii, as the name implies, is a 3 headed muscle on the posterior upper arm. It has a lateral, medial, and long head. The long head attaches to the scapula and ulna, trapping the humerus in-between them.

Brief Anatomy Overview

Origin

  • long head – infraglenoid tubercle of the scapula
  • medial head – posterior humeral shaft, medial to the radial groove
  • lateral head – posterior humeral shaft superolateral to the radial groove

Insertion

  • olecranon process of the ulna

Function

  • extension of the elbow
  • assists in extension and adduction of the shoulder joint

Innervation

  • medial, lateral heads – radial nerve (C5-T1)
  • Long head – axillary nerve (C5-C8)

The Triceps brachii is woven with the muscles and neurovascular bundle of the shoulder.

Attachment Details

Its attachments provide important landmarks for surgeons and bodyworkers. The long head trails along the radial nerve and leads to the radial groove of the humerus. This head also separates the teres major and minor as they extend from the scapula to connect on opposite sides of the humerus.

  • The long head attaches to the scapula at the base of the glenoid fossa. It blends with the capsule in this area. The blending both stabilizes the capsule and creates so potential for a torn labrum in jerky accidents.
  • The medial head attaches broadly on the surface of the humerus below the groove for the radial nerve. It also attaches to the intermuscular septum.
  • The lateral head attaches a ridge along the upper border of the radial groove. This ridge starts just medial to the attachment of teres minor. It extends interiorly and laterally to the deltoid tuberosity. This head also attaches to the intermuscular septum.
  • All three heads insert into the olecranon process of the ulna. This broad fascial attachment extends over the anconeus and blends with the fascial of the posterior forearm.

Anomalies, Etc.

Variations are reported as rare. Occasionally a fourth head is found in a cadaver study. The location of the 4th head is very inconsistent. They are mostly of interest in cases where they are positioned to compress the radial or ulna nerves.

Triceps innervation is often listed as the radial nerve. A more recent study shows that the axillary nerve often innervates the long head.

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